Port blue budding crystal formations (#57)

docs/AGE_PROFILES.md

@@ -109,6 +109,21 @@ write an Age using a biome where that mod registers its ore and verify the ore
 also appears more often. Check that Flat plus Dense Ores is rejected by the
 Binder and that a random, Link-Panel-only Age has no Dense Ores feature page.
 
+**Obelisks** adds Legacy-shaped, rare 4×4 plinths with a 2×2 shaft rising 12
+blocks, at most one attempt per 128 chunks per page. A preceding full-block
+Block page chooses the material; otherwise the Age seed chooses from valid
+block pages. Repeated Obelisks pages make independent attempts. Generation is
+deterministic and stays within one chunk; it requires a reasonably level,
+exposed solid surface, so Cave and Void terrain reject the page. Standard,
+Amplified, Sky Islands, and Flat terrain permit it. Page-free random surface
+Ages can roll Obelisks as one of their material features.
+
+For a visual check, write a Standard or Flat Age with an Obelisks page and
+search newly generated terrain for the 4×4 base and 12-block shaft. Try a
+Block page such as Obsidian immediately before Obelisks to verify its material
+changes. The Binder should reject Obelisks in Cave and Void Ages. Placement
+is deliberately rare, so several hundred fresh chunks may be needed.
+
 For an in-game visual check, bind Descriptive Books with a Link Panel,
 one of Standard, Amplified, Sky Islands, Flat, or Void terrain, and the Floating Islands
 feature page in that order. Fly through each Age at roughly Y=170–220 and

docs/ASSET_PROVENANCE.md

@@ -25,6 +25,9 @@ project's GNU LGPL v3 license. Rivencraft itself uses the same license.
 | `assets/rivencraft/textures/item/page_link_panel.png` | `page_background.png` and `PageBuilder.BasicPageSprite` | `9bc8ddc061845df0cd5ea47f4fdef773cff786ae` | Reproduces the legacy 160 px scale, black panel at `(25,30)`–`(135,75)`, and 128 px resample |
 | `assets/rivencraft/textures/gui/symbolcomponents.png` | `assets/mystcraft/textures/symbolcomponents.png` | `9bc8ddc061845df0cd5ea47f4fdef773cff786ae` | Byte-identical shared 512×512 component sheet for client-side page composition |
 | Runtime-composed symbol pages (`SymbolPageTextures`) | `page_background.png`, `textures/symbolcomponents.png`, `WordData`, `ModSymbols`, and `PageBuilder.PageSprite` | `9bc8ddc061845df0cd5ea47f4fdef773cff786ae` | Replaces the six pre-generated symbol PNGs; layers four poem words on the shared page background and caches bounded client textures |
+| `assets/rivencraft/textures/block/crystal_block.png`, `budding_crystal.png` | `assets/mystcraft/textures/blocks/crystal.png` | Legacy 0.13.7.06 local extraction | Exact 16×16 blue tile reused for both solid crystal blocks |
+| `assets/rivencraft/textures/block/{small,medium,large}_crystal_bud.png`, `crystal_cluster.png` | Minecraft 1.21.1 `textures/block/{small,medium,large}_amethyst_bud.png`, `amethyst_cluster.png` | Minecraft 1.21.1 | Original 16×16 alpha masks and silhouettes preserved; hue shifted toward Legacy blue, with brighter saturation; exported as 8-bit RGBA (not indexed PNG) |
+| `assets/rivencraft/textures/item/crystal_shard.png` | Original sprite generated with OpenAI ImageGen from the Legacy crystal palette | 2026-10-05 | Cropped and nearest-neighbor scaled to 16×16 |
 
 Mystcraft Legacy identifies XCompWiz as its project developer and includes the
 full LGPL v3 text in its root `LICENSE` file. Rivencraft's root `LICENSE`

docs/LEGACY_AGE_GRAMMAR_AUDIT.md

@@ -18,7 +18,7 @@ Legacy does **not** reject a book just because it omits terrain, biome, weather,
 | `WeatherNorm`, `Fast`, `Slow`, `Off`, `On`, `Cloudy`, `Rain`, `Snow`, `Storm` | `AgeTraits.Weather` has matching names except Legacy `On` maps to `ALWAYS` | Compile weather semantics separately from biome selection. `Snow` must remain deferred until optional season integration; do not silently substitute another weather mode. |
 | Suns, moons, starfields; angle, phase, period, color/gradient/sunset modifiers | One `celestialPeriod`, `celestialAngle`, `celestialPhase` on `AgeTraits` | Compile only the representable single-cycle subset first. Multiple celestial bodies, independent periods, custom stars, gradients and sunsets need a richer definition and renderer, not flattening into one value. |
 | Sky/fog/cloud/grass/foliage/water colors, natural variants, horizon, rainbow | Existing sky/dimension visuals and preview | Require an explicit modern client/biome-color design; metadata-only symbol pages must not pretend to change rendering. |
-| Caves, ores, huge trees, lakes, floating islands, tendrils, skylands, spheres, spikes, crystals; vanilla villages, strongholds, mineshafts, dungeons, fortresses, obelisks, fissures | Current cave profile, authored Floating Islands/Tendrils/Skylands/Spheres/Spikes, and page-gated vanilla Dungeons/Mineshafts/Nether Fortresses/Strongholds/Villages | The five Legacy vanilla structure symbols now gate Minecraft 1.21.1 generation. Dungeons use monster-room placement; the others use vanilla structure sets. Bespoke obelisks, fissures, crystals, and exact 1.12 structure geometry remain separate work. |
+| Caves, ores, huge trees, lakes, floating islands, tendrils, skylands, spheres, spikes, crystals; vanilla villages, strongholds, mineshafts, dungeons, fortresses, obelisks, fissures | Current cave profile, authored Floating Islands/Tendrils/Skylands/Spheres/Spikes/Obelisks/Crystal Formations and Dense Ores, and page-gated vanilla Dungeons/Mineshafts/Nether Fortresses/Strongholds/Villages | The five Legacy vanilla structure symbols gate Minecraft 1.21.1 generation. Dungeons use monster-room placement; the others use vanilla structure sets. Obelisks use a bespoke 4×4 plinth and 2×12×2 shaft with safe modern placement. Crystal Formations retain Legacy's blue tile and one-in-fifteen attempt rate but use new budding, shard-producing mounds. Fissures and exact 1.12 structure geometry remain separate work. |
 | `EnvAccel`, explosions, lightning, meteors, scorching; PvP and dummy suppression pages | No equivalent Age-definition effect | Defer environmental hazards/instability effects to milestone 6, PvP rule to a separately scoped server policy; retain authored IDs without fake behavior. |
 
 The Legacy symbol list and page names come from [ModSymbols](https://github.com/Mystcraft/Mystcraft-Legacy/blob/9bc8ddc061845df0cd5ea47f4fdef773cff786ae/src/main/java/com/xcompwiz/mystcraft/data/ModSymbols.java#L129-L240) and [SymbolRules](https://github.com/Mystcraft/Mystcraft-Legacy/blob/9bc8ddc061845df0cd5ea47f4fdef773cff786ae/src/main/java/com/xcompwiz/mystcraft/data/SymbolRules.java#L19-L137). Rivencraft's [catalog](../src/main/java/net/dnorberg/rivencraft/writing/SymbolCatalog.java) currently holds display metadata only; its built-in set is just standard terrain, native biomes, normal weather, normal lighting, normal time, and caves. [OrderedWriting](../src/main/java/net/dnorberg/rivencraft/writing/OrderedWriting.java) preserves page order, but no compiler yet connects it to [AgeTraits](../src/main/java/net/dnorberg/rivencraft/book/AgeTraits.java) or [Age profiles](AGE_PROFILES.md).

docs/WRITING_GRAMMAR.md

@@ -16,6 +16,8 @@ Feature pages come after the celestial section. Their order is retained in the p
 
 Flowers, Trees, Huge Trees, Rocks, Surface Lakes, Deep Lakes, and Small Lakes add vanilla placed features after normal biome decoration. Huge Trees currently use vanilla old-growth spruce placement as a modern approximation of Legacy's huge-tree page; it is not the custom Legacy tree generator. Without a preceding material page, Rocks select a valid solid block and each lake page selects a valid source-fluid block from the registered pool. The selection is deterministic for an Age seed and feature ID, so all chunks in that Age use the same material across restarts with the same block registry. The page-specific feature preserves vanilla placement rules other than the biome-list filter, since an authored page deliberately adds it to the Age. Surface and Small Lakes use a more visible one-in-twelve-chunks attempt rate instead of vanilla lava lakes' one-in-two-hundred; Deep Lakes retain their underground placement. Vanilla biome lava lakes are separate and can still appear alongside authored fluid lakes. These decorations require surface Noise terrain; Cave, Flat, and Void reject them. Flowers and both tree pages require at least one surface Overworld biome and only run in compatible chunks; Nether, End, and tagged cave biomes do not receive surface vegetation. Ravines add a separate Age-seeded vanilla canyon-carving pass to Noise terrain. Unsupported feature IDs and missing vanilla registry entries produce diagnostics instead of becoming no-ops.
 
-Material pages are generated for registered full-collision, non-fluid blocks and genuine source-fluid blocks, including eligible blocks supplied by other mods. Blocks with block entities are excluded. Waterlogged plants and coral are not fluid blocks and receive no pages. Valid source-fluid blocks appear only in the Fluid Pages creative tab; valid full-collision solids appear only in Block Pages. Both categories use the same saved material-page semantics. Put a Block Page immediately before Rocks to choose a rock material, or a Fluid Page immediately before Surface Lakes, Deep Lakes, or Small Lakes to choose a lake fluid. A material page left alone, placed before a different category, or attached to an incompatible feature is rejected. Both the feature and material ID are frozen in the saved plan, so future chunks retain their choice after restart. Existing chunks are not retroactively decorated. Custom structures, crystals, portals, and the Cave-terrain bug are outside this slice.
+Material pages are generated for registered full-collision, non-fluid blocks and genuine source-fluid blocks, including eligible blocks supplied by other mods. Blocks with block entities are excluded. Waterlogged plants and coral are not fluid blocks and receive no pages. Valid source-fluid blocks appear only in the Fluid Pages creative tab; valid full-collision solids appear only in Block Pages. Both categories use the same saved material-page semantics. Put a Block Page immediately before Rocks to choose a rock material, or a Fluid Page immediately before Surface Lakes, Deep Lakes, or Small Lakes to choose a lake fluid. A material page left alone, placed before a different category, or attached to an incompatible feature is rejected. Both the feature and material ID are frozen in the saved plan, so future chunks retain their choice after restart. Existing chunks are not retroactively decorated. Portals and the Cave-terrain bug remain separate work.
+
+Crystal Formations are an authored, material-free feature on exposed solid terrain, including Flat terrain; Cave and Void reject the page. Like Legacy, one in fifteen eligible chunks attempts a formation, with the site fixed by the Age seed and chunk coordinates. The modern formation is a compact mound with budding hearts instead of Legacy's long crystal lines. Budding blocks grow through small, medium, and large buds into clusters using vanilla amethyst timing and sounds. Non-silk cluster harvest yields Crystal Shards; four shards craft one Crystal Block. These blocks and shards use 16×16 textures: Legacy's crystal tile for solids and hue-shifted vanilla amethyst sprites for buds and clusters. A page-free Age can also randomly select Crystal Formations; an authored page always retains its exact choice in the saved plan.
 
 The Rivencraft symbol-page creative tabs read a generated index of bundled symbol definitions and group Pages by each definition's category, except biome-controller roles, which appear in a separate Biome Generation tab rather than the Biome tab. Adding another valid JSON symbol under `src/main/resources/data/rivencraft/rivencraft/symbols/` includes its page in the matching category tab on the next build; a new bundled category receives its own tab. Registry-derived Block and Fluid Pages have separate tabs and both appear in optional JEI. Link Pages have a separate tab. Blank Pages appear in neither the creative tabs nor JEI's ingredient list. The server catalog still decides whether a page is valid for writing. External server data-pack symbols are not included in this bundled index.

gradle.properties

@@ -36,7 +36,7 @@ mod_name=Rivencraft
 # The license of the mod. Review your options at https://choosealicense.com/. All Rights Reserved is the default.
 mod_license=LGPL-3.0-or-later
 # The mod version. Rivencraft uses the x.y.z.b policy documented in README.md.
-mod_version=0.4.16.0
+mod_version=0.4.18.2
 immersive_portals_version=6.0.7
 terrablender_version=4.1.0.8
 serene_seasons_version_id=B6nTjh4b

src/main/java/net/dnorberg/rivencraft/block/BuddingCrystalBlock.java

@@ -0,0 +1,45 @@
+package net.dnorberg.rivencraft.block;
+
+import net.dnorberg.rivencraft.registry.ModBlocks;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.Direction;
+import net.minecraft.server.level.ServerLevel;
+import net.minecraft.util.RandomSource;
+import net.minecraft.world.level.block.AmethystBlock;
+import net.minecraft.world.level.block.AmethystClusterBlock;
+import net.minecraft.world.level.block.Block;
+import net.minecraft.world.level.block.BuddingAmethystBlock;
+import net.minecraft.world.level.block.state.BlockBehaviour;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.material.Fluids;
+
+/** Vanilla amethyst growth, mapped to Rivencraft's blue crystal stages. */
+public final class BuddingCrystalBlock extends AmethystBlock {
+    public BuddingCrystalBlock(BlockBehaviour.Properties properties) {
+        super(properties);
+    }
+
+    @Override
+    protected void randomTick(BlockState state, ServerLevel level, BlockPos pos, RandomSource random) {
+        if (random.nextInt(5) != 0) return;
+        Direction direction = Direction.values()[random.nextInt(Direction.values().length)];
+        BlockPos target = pos.relative(direction);
+        BlockState existing = level.getBlockState(target);
+        Block next = nextStage(existing, direction);
+        if (next == null) return;
+        level.setBlockAndUpdate(target, next.defaultBlockState()
+                .setValue(AmethystClusterBlock.FACING, direction)
+                .setValue(AmethystClusterBlock.WATERLOGGED,
+                        existing.getFluidState().getType() == Fluids.WATER));
+    }
+
+    public static Block nextStage(BlockState existing, Direction direction) {
+        if (BuddingAmethystBlock.canClusterGrowAtState(existing)) return ModBlocks.SMALL_CRYSTAL_BUD.get();
+        if (!existing.hasProperty(AmethystClusterBlock.FACING)
+                || existing.getValue(AmethystClusterBlock.FACING) != direction) return null;
+        if (existing.is(ModBlocks.SMALL_CRYSTAL_BUD)) return ModBlocks.MEDIUM_CRYSTAL_BUD.get();
+        if (existing.is(ModBlocks.MEDIUM_CRYSTAL_BUD)) return ModBlocks.LARGE_CRYSTAL_BUD.get();
+        if (existing.is(ModBlocks.LARGE_CRYSTAL_BUD)) return ModBlocks.CRYSTAL_CLUSTER.get();
+        return null;
+    }
+}

src/main/java/net/dnorberg/rivencraft/book/AgeFeatureSelection.java

@@ -27,10 +27,12 @@ import net.minecraft.world.level.block.Blocks;
 /** Validates and freezes supported feature pages and their preceding material modifiers. */
 public final class AgeFeatureSelection {
     private static final List<ResourceLocation> BLOCK_FEATURES = List.of(
-            id("rocks"), id("floating_islands"), id("tendrils"), id("spheres"), id("spikes"));
+            id("rocks"), id("floating_islands"), id("tendrils"), id("spheres"), id("spikes"),
+            id("obelisks"));
     private static final List<ResourceLocation> FLUID_FEATURES = List.of(
             id("surface_lakes"), id("deep_lakes"), id("lava_lakes"));
     private static final long RANDOM_SKYLANDS_SALT = 0x534B594C414E4453L;
+    public static final ResourceLocation CRYSTAL_FORMATIONS = id("crystal_formations");
 
     private AgeFeatureSelection() {}
 
@@ -121,6 +123,8 @@ public final class AgeFeatureSelection {
 
     private static boolean compatible(ResourceLocation feature, AgeRuntimeProfile profile) {
         if (tendrils(feature) || spheres(feature)) return true;
+        if (obelisks(feature)) return !AgeBiomeSelection.isCave(profile)
+                && profile.terrain() != AgeRuntimeProfile.Terrain.VOID;
         if (AgeBiomeSelection.isCave(profile)) return false;
         if (spikes(feature)) return profile.terrain() != AgeRuntimeProfile.Terrain.VOID;
         return floatingIslands(feature) || profile.terrain() == AgeRuntimeProfile.Terrain.NOISE;
@@ -136,7 +140,8 @@ public final class AgeFeatureSelection {
             if (choice.material().isPresent()
                     || !isRock(choice.id()) && !isLake(choice.id())
                     && !floatingIslands(choice.id()) && !tendrils(choice.id())
-                    && !spheres(choice.id()) && !spikes(choice.id())) {
+                    && !spheres(choice.id()) && !spikes(choice.id())
+                    && !obelisks(choice.id())) {
                 resolved.add(choice);
                 continue;
             }
@@ -169,6 +174,8 @@ public final class AgeFeatureSelection {
         if (profile.terrain() == AgeRuntimeProfile.Terrain.NOISE
                 && Math.floorMod(mix(ageSeed ^ RANDOM_SKYLANDS_SALT), 8) == 0)
             choices.add(new Choice(id("skylands"), Optional.empty()));
+        if (error(CRYSTAL_FORMATIONS, profile, registries) == null && random.nextInt(10) == 0)
+            choices.add(new Choice(CRYSTAL_FORMATIONS, Optional.empty()));
         AgeBiomeSelection biomes = AgeBiomeSelection.compile(WritingGrammar.parse(OrderedWriting.EMPTY),
                 AgeTraits.select(ageSeed), profile, ageSeed, registries);
         choices.addAll(AgeStructureSelection.randomChoices(ageSeed, profile, biomes, registries));
@@ -200,6 +207,11 @@ public final class AgeFeatureSelection {
             return AgeStructureSelection.error(choice, profile, null, registries);
         if (choice.equals(AgeDenseOres.ID))
             return AgeDenseOres.error(profile, null, registries);
+        if (choice.equals(CRYSTAL_FORMATIONS)) {
+            if (AgeBiomeSelection.isCave(profile) || profile.terrain() == AgeRuntimeProfile.Terrain.VOID)
+                return "Feature " + choice + " needs exposed solid ground, not Cave or Void terrain";
+            return null;
+        }
         if (skylands(choice)) return null;
         if (tendrils(choice)) return null;
         if (spheres(choice)) return null;
@@ -208,6 +220,11 @@ public final class AgeFeatureSelection {
                 return "Feature " + choice + " needs an exposed solid surface, not Cave or Void terrain";
             return null;
         }
+        if (obelisks(choice)) {
+            if (AgeBiomeSelection.isCave(profile) || profile.terrain() == AgeRuntimeProfile.Terrain.VOID)
+                return "Feature " + choice + " needs exposed solid surface terrain, not Cave or Void";
+            return null;
+        }
         if (floatingIslands(choice)) {
             if (AgeBiomeSelection.isCave(profile))
                 return "Feature " + choice + " cannot form above Cave terrain";
@@ -298,9 +315,13 @@ public final class AgeFeatureSelection {
         return choice.equals(id("spikes"));
     }
 
+    public static boolean obelisks(ResourceLocation choice) {
+        return choice.equals(id("obelisks"));
+    }
+
     private static boolean solidFeature(ResourceLocation choice) {
         return isRock(choice) || floatingIslands(choice) || tendrils(choice)
-                || spheres(choice) || spikes(choice);
+                || spheres(choice) || spikes(choice) || obelisks(choice);
     }
 
     public static boolean skylands(ResourceLocation choice) {

src/main/java/net/dnorberg/rivencraft/book/FeatureWritingGameTests.java

@@ -40,7 +40,7 @@ public final class FeatureWritingGameTests {
                 "feature/bastions", "feature/buried_treasure", "feature/shipwrecks",
                 "feature/ocean_ruins", "feature/pillager_outposts", "feature/ruined_portals",
                 "feature/nether_fossils", "feature/ancient_cities", "feature/trail_ruins",
-                "feature/dense_ores");
+                "feature/dense_ores", "feature/obelisks", "feature/crystal_formations");
         helper.assertTrue(PageItem.bundledCreativeSymbols().containsAll(pages),
                 "Supported feature pages must appear in the creative and JEI symbol feed");
         for (String path : pages) {
@@ -72,6 +72,8 @@ public final class FeatureWritingGameTests {
                     || AgeFeatureSelection.skylands(choice.id())
                     || AgeFeatureSelection.spheres(choice.id())
                     || AgeFeatureSelection.spikes(choice.id())
+                    || AgeFeatureSelection.obelisks(choice.id())
+                    || choice.id().equals(AgeFeatureSelection.CRYSTAL_FORMATIONS)
                     || choice.id().equals(AgeDenseOres.ID)) continue;
             var placement = AgeFeatureSelection.placedFeature(choice.id());
             helper.assertTrue(registries.lookupOrThrow(Registries.PLACED_FEATURE)
@@ -419,7 +421,8 @@ public final class FeatureWritingGameTests {
                             || AgeFeatureSelection.floatingIslands(choices.getFirst().id())
                             || AgeFeatureSelection.tendrils(choices.getFirst().id())
                             || AgeFeatureSelection.spheres(choices.getFirst().id())
-                            || AgeFeatureSelection.spikes(choices.getFirst().id()),
+                            || AgeFeatureSelection.spikes(choices.getFirst().id())
+                            || AgeFeatureSelection.obelisks(choices.getFirst().id()),
                     "The inferred feature must accept the material type");
             helper.assertValueEqual(AgeFeatureSelection.resolved(AgeGenerationPlan.load(plan.save())), choices,
                     "The inferred feature must be deterministic across a plan reload");

src/main/java/net/dnorberg/rivencraft/client/ClientEvents.java

@@ -2,9 +2,12 @@ package net.dnorberg.rivencraft.client;
 
 import net.dnorberg.rivencraft.Rivencraft;
 import net.dnorberg.rivencraft.registry.ModBlockEntities;
+import net.dnorberg.rivencraft.registry.ModBlocks;
 import net.dnorberg.rivencraft.registry.ModDataComponents;
 import net.dnorberg.rivencraft.registry.ModItems;
 import net.minecraft.client.renderer.item.ItemProperties;
+import net.minecraft.client.renderer.ItemBlockRenderTypes;
+import net.minecraft.client.renderer.RenderType;
 import net.minecraft.resources.ResourceLocation;
 import net.neoforged.api.distmarker.Dist;
 import net.neoforged.bus.api.SubscribeEvent;
@@ -62,11 +65,18 @@ public final class ClientEvents {
 
     @SubscribeEvent
     public static void clientSetup(FMLClientSetupEvent event) {
-        event.enqueueWork(() -> ItemProperties.register(
+        event.enqueueWork(() -> {
-                ModItems.LINKING_BOOK.get(),
+            ItemProperties.register(
-                ResourceLocation.fromNamespaceAndPath(Rivencraft.MOD_ID, "bound"),
+                    ModItems.LINKING_BOOK.get(),
-                (stack, level, entity, seed) -> stack.has(ModDataComponents.LINK_TARGET.get()) ? 1.0F : 0.0F
+                    ResourceLocation.fromNamespaceAndPath(Rivencraft.MOD_ID, "bound"),
-        ));
+                    (stack, level, entity, seed) -> stack.has(ModDataComponents.LINK_TARGET.get()) ? 1.0F : 0.0F
+            );
+            // Some renderers still query the block layer instead of the model's render_type hint.
+            ItemBlockRenderTypes.setRenderLayer(ModBlocks.SMALL_CRYSTAL_BUD.get(), RenderType.cutout());
+            ItemBlockRenderTypes.setRenderLayer(ModBlocks.MEDIUM_CRYSTAL_BUD.get(), RenderType.cutout());
+            ItemBlockRenderTypes.setRenderLayer(ModBlocks.LARGE_CRYSTAL_BUD.get(), RenderType.cutout());
+            ItemBlockRenderTypes.setRenderLayer(ModBlocks.CRYSTAL_CLUSTER.get(), RenderType.cutout());
+        });
         NeoForge.EVENT_BUS.addListener(ClientBookInteractionHandler::onRightClickItem);
         NeoForge.EVENT_BUS.addListener(ClientBookInteractionHandler::onRightClickBlock);
         NeoForge.EVENT_BUS.addListener(ClientBookExploreOverlay::onClientTickPre);

src/main/java/net/dnorberg/rivencraft/registry/ModBlocks.java

@@ -5,7 +5,11 @@ import net.dnorberg.rivencraft.block.BookStandBlock;
 import net.dnorberg.rivencraft.block.BookBinderBlock;
 import net.dnorberg.rivencraft.block.WritingDeskBlock;
 import net.dnorberg.rivencraft.block.InkMixerBlock;
+import net.dnorberg.rivencraft.block.BuddingCrystalBlock;
+import net.minecraft.world.level.block.AmethystClusterBlock;
+import net.minecraft.world.level.block.Block;
 import net.minecraft.world.level.block.Blocks;
+import net.minecraft.world.level.material.MapColor;
 import net.minecraft.world.level.block.state.BlockBehaviour;
 import net.neoforged.bus.api.IEventBus;
 import net.neoforged.neoforge.registries.DeferredBlock;
@@ -31,6 +35,23 @@ public final class ModBlocks {
             "ink_mixer", InkMixerBlock::new,
             BlockBehaviour.Properties.ofFullCopy(Blocks.CRAFTING_TABLE).noOcclusion()
     );
+    public static final DeferredBlock<Block> CRYSTAL_BLOCK = BLOCKS.registerBlock("crystal_block",
+            Block::new, BlockBehaviour.Properties.ofFullCopy(Blocks.AMETHYST_BLOCK).mapColor(MapColor.COLOR_BLUE));
+    public static final DeferredBlock<BuddingCrystalBlock> BUDDING_CRYSTAL = BLOCKS.registerBlock("budding_crystal",
+            BuddingCrystalBlock::new, BlockBehaviour.Properties.ofFullCopy(Blocks.BUDDING_AMETHYST)
+                    .mapColor(MapColor.COLOR_BLUE));
+    public static final DeferredBlock<AmethystClusterBlock> CRYSTAL_CLUSTER = BLOCKS.registerBlock("crystal_cluster",
+            properties -> new AmethystClusterBlock(7.0F, 3.0F, properties),
+            BlockBehaviour.Properties.ofFullCopy(Blocks.AMETHYST_CLUSTER));
+    public static final DeferredBlock<AmethystClusterBlock> LARGE_CRYSTAL_BUD = BLOCKS.registerBlock("large_crystal_bud",
+            properties -> new AmethystClusterBlock(5.0F, 3.0F, properties),
+            BlockBehaviour.Properties.ofFullCopy(Blocks.LARGE_AMETHYST_BUD));
+    public static final DeferredBlock<AmethystClusterBlock> MEDIUM_CRYSTAL_BUD = BLOCKS.registerBlock("medium_crystal_bud",
+            properties -> new AmethystClusterBlock(4.0F, 3.0F, properties),
+            BlockBehaviour.Properties.ofFullCopy(Blocks.MEDIUM_AMETHYST_BUD));
+    public static final DeferredBlock<AmethystClusterBlock> SMALL_CRYSTAL_BUD = BLOCKS.registerBlock("small_crystal_bud",
+            properties -> new AmethystClusterBlock(3.0F, 4.0F, properties),
+            BlockBehaviour.Properties.ofFullCopy(Blocks.SMALL_AMETHYST_BUD));
 
     private ModBlocks() {
     }

src/main/java/net/dnorberg/rivencraft/registry/ModCreativeTabs.java

@@ -31,6 +31,13 @@ public final class ModCreativeTabs {
                         output.accept(ModItems.WRITING_DESK.get());
                         output.accept(ModItems.INK_MIXER.get());
                         output.accept(ModItems.BOOK_BINDER.get());
+                        output.accept(ModItems.CRYSTAL_BLOCK.get());
+                        output.accept(ModItems.BUDDING_CRYSTAL.get());
+                        output.accept(ModItems.CRYSTAL_CLUSTER.get());
+                        output.accept(ModItems.LARGE_CRYSTAL_BUD.get());
+                        output.accept(ModItems.MEDIUM_CRYSTAL_BUD.get());
+                        output.accept(ModItems.SMALL_CRYSTAL_BUD.get());
+                        output.accept(ModItems.CRYSTAL_SHARD.get());
                     })
                     .build());
 

src/main/java/net/dnorberg/rivencraft/registry/ModItems.java

@@ -43,6 +43,13 @@ public final class ModItems {
     public static final DeferredItem<BlockItem> WRITING_DESK = ITEMS.registerSimpleBlockItem(ModBlocks.WRITING_DESK);
     public static final DeferredItem<BlockItem> BOOK_BINDER = ITEMS.registerSimpleBlockItem(ModBlocks.BOOK_BINDER);
     public static final DeferredItem<BlockItem> INK_MIXER = ITEMS.registerSimpleBlockItem(ModBlocks.INK_MIXER);
+    public static final DeferredItem<BlockItem> CRYSTAL_BLOCK = ITEMS.registerSimpleBlockItem(ModBlocks.CRYSTAL_BLOCK);
+    public static final DeferredItem<BlockItem> BUDDING_CRYSTAL = ITEMS.registerSimpleBlockItem(ModBlocks.BUDDING_CRYSTAL);
+    public static final DeferredItem<BlockItem> CRYSTAL_CLUSTER = ITEMS.registerSimpleBlockItem(ModBlocks.CRYSTAL_CLUSTER);
+    public static final DeferredItem<BlockItem> LARGE_CRYSTAL_BUD = ITEMS.registerSimpleBlockItem(ModBlocks.LARGE_CRYSTAL_BUD);
+    public static final DeferredItem<BlockItem> MEDIUM_CRYSTAL_BUD = ITEMS.registerSimpleBlockItem(ModBlocks.MEDIUM_CRYSTAL_BUD);
+    public static final DeferredItem<BlockItem> SMALL_CRYSTAL_BUD = ITEMS.registerSimpleBlockItem(ModBlocks.SMALL_CRYSTAL_BUD);
+    public static final DeferredItem<Item> CRYSTAL_SHARD = ITEMS.registerSimpleItem("crystal_shard");
 
     private ModItems() {
     }

src/main/java/net/dnorberg/rivencraft/world/AgeFeatureChunkGenerator.java

@@ -162,6 +162,8 @@ public final class AgeFeatureChunkGenerator extends NoiseBasedChunkGenerator {
         BlockPos origin = new BlockPos(x, level.getMinBuildHeight(), z);
         Map<AgeFeatureSelection.Choice, Integer> occurrences = new HashMap<>();
         Map<ResourceLocation, Integer> spikeOccurrences = new HashMap<>();
+        int obeliskOccurrence = 0;
+        int crystalOccurrence = 0;
         for (int index = 0; index < features.size(); index++) {
             AgeFeatureSelection.Choice choice = features.get(index);
             int occurrence = occurrences.merge(choice, 1, Integer::sum) - 1;
@@ -170,6 +172,14 @@ public final class AgeFeatureChunkGenerator extends NoiseBasedChunkGenerator {
                         spikeOccurrences.merge(choice.id(), 1, Integer::sum) - 1);
                 continue;
             }
+            if (AgeFeatureSelection.obelisks(choice.id())) {
+                ObelisksFeature.generate(level, chunk, ageSeed, choice, obeliskOccurrence++);
+                continue;
+            }
+            if (choice.id().equals(AgeFeatureSelection.CRYSTAL_FORMATIONS)) {
+                CrystalFormationsFeature.generate(level, chunk, ageSeed, crystalOccurrence++);
+                continue;
+            }
             if (choice.id().equals(AgeDenseOres.ID)) {
                 AgeDenseOres.place(level, chunk, this, ageSeed, occurrence);
                 continue;

src/main/java/net/dnorberg/rivencraft/world/AgeFlatChunkGenerator.java

@@ -124,10 +124,13 @@ public final class AgeFlatChunkGenerator extends ChunkGenerator {
     @Override
     public void applyBiomeDecoration(WorldGenLevel level, ChunkAccess chunk, StructureManager structures) {
         super.applyBiomeDecoration(level, chunk, structures);
-        int occurrence = 0;
+        int spikeOccurrence = 0;
+        int obeliskOccurrence = 0;
         for (AgeFeatureSelection.Choice choice : features) {
             if (AgeFeatureSelection.spikes(choice.id()))
-                SpikesFeature.generate(level, chunk, ageSeed, choice, occurrence++);
+                SpikesFeature.generate(level, chunk, ageSeed, choice, spikeOccurrence++);
+            if (AgeFeatureSelection.obelisks(choice.id()))
+                ObelisksFeature.generate(level, chunk, ageSeed, choice, obeliskOccurrence++);
         }
     }
 

src/main/java/net/dnorberg/rivencraft/world/CrystalFormationsFeature.java

@@ -0,0 +1,82 @@
+package net.dnorberg.rivencraft.world;
+
+import net.dnorberg.rivencraft.registry.ModBlocks;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.Direction;
+import net.minecraft.util.RandomSource;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.WorldGenLevel;
+import net.minecraft.world.level.block.AmethystClusterBlock;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import net.minecraft.world.level.levelgen.Heightmap;
+
+/** A surface crystal mound with budding hearts and initially seeded buds. */
+final class CrystalFormationsFeature {
+    private static final long SALT = 0x4352595354414C53L;
+    private static final int CHANCE = 15; // Legacy's authored crystal formation frequency.
+
+    private CrystalFormationsFeature() {}
+
+    record Site(int x, int z, long seed) {}
+
+    static Site site(long ageSeed, ChunkPos chunk, int occurrence) {
+        long seed = mix(ageSeed ^ SALT ^ (long) chunk.x * 341873128712L
+                ^ (long) chunk.z * 132897987541L ^ (long) occurrence * 0x9E3779B97F4A7C15L);
+        RandomSource random = RandomSource.create(seed);
+        if (random.nextInt(CHANCE) != 0) return null;
+        return new Site(chunk.getMinBlockX() + 5 + random.nextInt(6),
+                chunk.getMinBlockZ() + 5 + random.nextInt(6), seed);
+    }
+
+    static void generate(WorldGenLevel level, ChunkAccess chunk, long ageSeed, int occurrence) {
+        Site site = site(ageSeed, chunk.getPos(), occurrence);
+        if (site == null) return;
+        RandomSource random = RandomSource.create(site.seed() ^ 0x42554444494E474CL);
+        int y = level.getHeight(Heightmap.Types.WORLD_SURFACE_WG, site.x(), site.z());
+        if (y <= level.getMinBuildHeight() + 1 || y + 4 >= level.getMaxBuildHeight()) return;
+        BlockPos.MutableBlockPos pos = new BlockPos.MutableBlockPos();
+        for (int dx = -1; dx <= 1; dx++) {
+            for (int dz = -1; dz <= 1; dz++) {
+                int x = site.x() + dx;
+                int z = site.z() + dz;
+                if (Math.abs(level.getHeight(Heightmap.Types.WORLD_SURFACE_WG, x, z) - y) > 1) return;
+                BlockState floor = level.getBlockState(pos.set(x, y - 1, z));
+                if (!floor.isFaceSturdy(level, pos, Direction.UP) || !floor.getFluidState().isEmpty()
+                        || floor.hasBlockEntity()) return;
+                for (int h = 0; h < 4; h++) {
+                    BlockState existing = level.getBlockState(pos.set(x, y + h, z));
+                    if (!existing.isAir() && !existing.canBeReplaced()) return;
+                }
+            }
+        }
+        for (int dx = -1; dx <= 1; dx++) {
+            for (int dz = -1; dz <= 1; dz++) {
+                boolean center = dx == 0 && dz == 0;
+                int height = center ? 3 : random.nextInt(3) == 0 ? 2 : 1;
+                for (int h = 0; h < height; h++) {
+                    boolean budding = h == height - 1 && (center || random.nextBoolean());
+                    level.setBlock(pos.set(site.x() + dx, y + h, site.z() + dz),
+                            budding ? ModBlocks.BUDDING_CRYSTAL.get().defaultBlockState()
+                                    : ModBlocks.CRYSTAL_BLOCK.get().defaultBlockState(), 2);
+                }
+                if (buddingTop(level.getBlockState(pos.set(site.x() + dx, y + height - 1, site.z() + dz)))
+                        && random.nextBoolean()) {
+                    level.setBlock(pos.set(site.x() + dx, y + height, site.z() + dz),
+                            ModBlocks.SMALL_CRYSTAL_BUD.get().defaultBlockState()
+                                    .setValue(AmethystClusterBlock.FACING, Direction.UP), 2);
+                }
+            }
+        }
+    }
+
+    private static boolean buddingTop(BlockState state) {
+        return state.is(ModBlocks.BUDDING_CRYSTAL);
+    }
+
+    private static long mix(long value) {
+        value = (value ^ value >>> 30) * 0xBF58476D1CE4E5B9L;
+        value = (value ^ value >>> 27) * 0x94D049BB133111EBL;
+        return value ^ value >>> 31;
+    }
+}

src/main/java/net/dnorberg/rivencraft/world/CrystalFormationsGameTests.java

@@ -0,0 +1,75 @@
+package net.dnorberg.rivencraft.world;
+
+import java.util.List;
+import java.util.Objects;
+import net.dnorberg.rivencraft.Rivencraft;
+import net.dnorberg.rivencraft.block.BuddingCrystalBlock;
+import net.dnorberg.rivencraft.book.AgeFeatureSelection;
+import net.dnorberg.rivencraft.book.AgeGenerationPlan;
+import net.dnorberg.rivencraft.book.AgeGenerationProfiles;
+import net.dnorberg.rivencraft.book.AgeTraits;
+import net.dnorberg.rivencraft.item.PageItem;
+import net.dnorberg.rivencraft.registry.ModBlocks;
+import net.dnorberg.rivencraft.writing.OrderedWriting;
+import net.dnorberg.rivencraft.writing.SymbolReference;
+import net.dnorberg.rivencraft.writing.WritingEntry;
+import net.minecraft.core.Direction;
+import net.minecraft.gametest.framework.GameTest;
+import net.minecraft.gametest.framework.GameTestHelper;
+import net.minecraft.resources.ResourceLocation;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.block.AmethystClusterBlock;
+import net.minecraft.world.level.block.Blocks;
+import net.neoforged.neoforge.gametest.GameTestHolder;
+import net.neoforged.neoforge.gametest.PrefixGameTestTemplate;
+
+@GameTestHolder(Rivencraft.MOD_ID)
+@PrefixGameTestTemplate(false)
+public final class CrystalFormationsGameTests {
+    private CrystalFormationsGameTests() {}
+
+    @GameTest(template = "empty")
+    public static void authoredCrystalPageAndGrowth(GameTestHelper helper) {
+        var page = PageItem.createBundledCreativePage("feature/crystal_formations");
+        helper.assertTrue(PageItem.isUsableWriting(page), "Crystal Formations page must be writable");
+        var plan = AgeGenerationPlan.compile(new OrderedWriting(List.of(
+                        WritingEntry.linkPanel(),
+                        WritingEntry.symbol(new SymbolReference(ResourceLocation.fromNamespaceAndPath(
+                                Rivencraft.MOD_ID, "terrain/standard"))),
+                        WritingEntry.symbol(new SymbolReference(ResourceLocation.fromNamespaceAndPath(
+                                Rivencraft.MOD_ID, "feature/crystal_formations"))))),
+                57L, AgeGenerationProfiles.STANDARD, AgeTraits.select(57L),
+                helper.getLevel().registryAccess());
+        helper.assertValueEqual(AgeFeatureSelection.resolved(plan).getFirst().id(),
+                AgeFeatureSelection.CRYSTAL_FORMATIONS, "Page must compile to the crystal feature");
+        helper.assertValueEqual(AgeFeatureSelection.resolved(AgeGenerationPlan.load(plan.save())),
+                AgeFeatureSelection.resolved(plan), "Crystal choice must survive saving");
+        helper.assertValueEqual(BuddingCrystalBlock.nextStage(Blocks.AIR.defaultBlockState(), Direction.UP),
+                ModBlocks.SMALL_CRYSTAL_BUD.get(), "Air must begin the blue bud sequence");
+        helper.assertValueEqual(BuddingCrystalBlock.nextStage(
+                        ModBlocks.SMALL_CRYSTAL_BUD.get().defaultBlockState()
+                                .setValue(AmethystClusterBlock.FACING, Direction.UP), Direction.UP),
+                ModBlocks.MEDIUM_CRYSTAL_BUD.get(), "Small buds must grow into medium buds");
+        helper.assertValueEqual(BuddingCrystalBlock.nextStage(
+                        ModBlocks.MEDIUM_CRYSTAL_BUD.get().defaultBlockState()
+                                .setValue(AmethystClusterBlock.FACING, Direction.UP), Direction.UP),
+                ModBlocks.LARGE_CRYSTAL_BUD.get(), "Medium buds must grow into large buds");
+        helper.assertValueEqual(BuddingCrystalBlock.nextStage(
+                        ModBlocks.LARGE_CRYSTAL_BUD.get().defaultBlockState()
+                                .setValue(AmethystClusterBlock.FACING, Direction.UP), Direction.UP),
+                ModBlocks.CRYSTAL_CLUSTER.get(), "Large buds must grow into shard-bearing clusters");
+        helper.assertTrue(BuddingCrystalBlock.nextStage(
+                        ModBlocks.LARGE_CRYSTAL_BUD.get().defaultBlockState()
+                                .setValue(AmethystClusterBlock.FACING, Direction.NORTH), Direction.UP) == null,
+                "Growth must not change a bud facing away from its budding block");
+        helper.assertTrue(ModBlocks.BUDDING_CRYSTAL.get().defaultBlockState().isRandomlyTicking(),
+                "Budding crystals must receive random growth ticks");
+        var site = CrystalFormationsFeature.site(57L, new ChunkPos(10, -3), 0);
+        helper.assertTrue(Objects.equals(site, CrystalFormationsFeature.site(57L, new ChunkPos(10, -3), 0)),
+                "Formation placement must be deterministic per Age and chunk");
+        helper.assertTrue(java.util.stream.IntStream.range(0, 100).anyMatch(x ->
+                        CrystalFormationsFeature.site(57L, new ChunkPos(x, -3), 0) != null),
+                "Authored crystal formations must have reachable placement sites");
+        helper.succeed();
+    }
+}

src/main/java/net/dnorberg/rivencraft/world/ObelisksFeature.java

@@ -0,0 +1,95 @@
+package net.dnorberg.rivencraft.world;
+
+import net.dnorberg.rivencraft.book.AgeFeatureSelection;
+import net.minecraft.core.BlockPos;
+import net.minecraft.core.Direction;
+import net.minecraft.core.registries.BuiltInRegistries;
+import net.minecraft.util.RandomSource;
+import net.minecraft.world.level.ChunkPos;
+import net.minecraft.world.level.WorldGenLevel;
+import net.minecraft.world.level.block.state.BlockState;
+import net.minecraft.world.level.chunk.ChunkAccess;
+import net.minecraft.world.level.levelgen.Heightmap;
+
+/** Rare one-chunk obelisk adapted from Legacy's 4x4 plinth and 2x12x2 shaft. */
+final class ObelisksFeature {
+    private static final long SALT = 0x4F42454C49534B53L;
+    private static final int CHANCE = 128;
+    private static final int BASE = 4;
+    private static final int HEIGHT = 12;
+
+    private ObelisksFeature() {}
+
+    record Site(int x, int z) {}
+
+    static Site site(long ageSeed, ChunkPos chunk, int occurrence) {
+        RandomSource random = RandomSource.create(mix(ageSeed ^ SALT
+                ^ (long) chunk.x * 341873128712L ^ (long) chunk.z * 132897987541L
+                ^ (long) occurrence * 0x9E3779B97F4A7C15L));
+        if (random.nextInt(CHANCE) != 0) return null;
+        return new Site(chunk.getMinBlockX() + 4 + random.nextInt(8),
+                chunk.getMinBlockZ() + 4 + random.nextInt(8));
+    }
+
+    static void generate(WorldGenLevel level, ChunkAccess chunk, long ageSeed,
+                         AgeFeatureSelection.Choice choice, int occurrence) {
+        Site site = site(ageSeed, chunk.getPos(), occurrence);
+        if (site == null || choice.material().isEmpty()) return;
+        BlockState material = BuiltInRegistries.BLOCK.get(choice.material().orElseThrow()).defaultBlockState();
+        BlockPos.MutableBlockPos pos = new BlockPos.MutableBlockPos();
+        int minSurface = Integer.MAX_VALUE;
+        int maxSurface = Integer.MIN_VALUE;
+        int[][] surface = new int[BASE][BASE];
+        for (int dx = 0; dx < BASE; dx++) {
+            for (int dz = 0; dz < BASE; dz++) {
+                int x = site.x() + dx;
+                int z = site.z() + dz;
+                int y = level.getHeight(Heightmap.Types.WORLD_SURFACE_WG, x, z);
+                if (y <= level.getMinBuildHeight() + 1) return;
+                BlockState ground = level.getBlockState(pos.set(x, y - 1, z));
+                if (!ground.isFaceSturdy(level, pos, Direction.UP)
+                        || !ground.getFluidState().isEmpty() || ground.hasBlockEntity()) return;
+                surface[dx][dz] = y;
+                minSurface = Math.min(minSurface, y);
+                maxSurface = Math.max(maxSurface, y);
+            }
+        }
+        if (maxSurface - minSurface > 2 || maxSurface + HEIGHT >= level.getMaxBuildHeight()) return;
+        for (int dx = 0; dx < BASE; dx++) {
+            for (int dz = 0; dz < BASE; dz++) {
+                for (int y = surface[dx][dz]; y <= maxSurface; y++) {
+                    if (!open(level.getBlockState(pos.set(site.x() + dx, y, site.z() + dz)))) return;
+                }
+            }
+        }
+        for (int dx = 1; dx <= 2; dx++) {
+            for (int dz = 1; dz <= 2; dz++) {
+                for (int y = maxSurface + 1; y <= maxSurface + HEIGHT; y++) {
+                    if (!open(level.getBlockState(pos.set(site.x() + dx, y, site.z() + dz)))) return;
+                }
+            }
+        }
+        for (int dx = 0; dx < BASE; dx++) {
+            for (int dz = 0; dz < BASE; dz++) {
+                for (int y = surface[dx][dz]; y <= maxSurface; y++)
+                    level.setBlock(pos.set(site.x() + dx, y, site.z() + dz), material, 2);
+            }
+        }
+        for (int dx = 1; dx <= 2; dx++) {
+            for (int dz = 1; dz <= 2; dz++) {
+                for (int y = maxSurface + 1; y <= maxSurface + HEIGHT; y++)
+                    level.setBlock(pos.set(site.x() + dx, y, site.z() + dz), material, 2);
+            }
+        }
+    }
+
+    private static boolean open(BlockState state) {
+        return state.getFluidState().isEmpty() && (state.isAir() || state.canBeReplaced());
+    }
+
+    private static long mix(long value) {
+        value = (value ^ value >>> 30) * 0xBF58476D1CE4E5B9L;
+        value = (value ^ value >>> 27) * 0x94D049BB133111EBL;
+        return value ^ value >>> 31;
+    }
+}

src/main/java/net/dnorberg/rivencraft/world/ObelisksGameTests.java

@@ -0,0 +1,110 @@
+package net.dnorberg.rivencraft.world;
+
+import java.util.List;
+import java.util.Optional;
+import net.dnorberg.rivencraft.Rivencraft;
+import net.dnorberg.rivencraft.book.AgeFeatureSelection;
+import net.dnorberg.rivencraft.book.AgeGenerationPlan;
+import net.dnorberg.rivencraft.book.AgeGenerationProfiles;
+import net.dnorberg.rivencraft.book.AgeRuntimeProfiles;
+import net.dnorberg.rivencraft.book.AgeTraits;
+import net.dnorberg.rivencraft.item.PageItem;
+import net.dnorberg.rivencraft.writing.OrderedWriting;
+import net.dnorberg.rivencraft.writing.SymbolReference;
+import net.dnorberg.rivencraft.writing.WritingEntry;
+import net.minecraft.gametest.framework.GameTest;
+import net.minecraft.gametest.framework.GameTestHelper;
+import net.minecraft.resources.ResourceLocation;
+import net.minecraft.world.level.ChunkPos;
+import net.neoforged.neoforge.gametest.GameTestHolder;
+import net.neoforged.neoforge.gametest.PrefixGameTestTemplate;
+
+/** Obelisks must retain ordered materials and generate a stable Legacy-sized shape. */
+@GameTestHolder(Rivencraft.MOD_ID)
+@PrefixGameTestTemplate(false)
+public final class ObelisksGameTests {
+    private ObelisksGameTests() {}
+
+    @GameTest(template = "empty")
+    public static void authoredObelisksKeepTheirMaterialAndTerrainRules(GameTestHelper helper) {
+        var registries = helper.getLevel().registryAccess();
+        helper.assertTrue(PageItem.bundledCreativeSymbols().contains("feature/obelisks"),
+                "Obelisks must appear in the Creative and JEI symbol feed");
+        OrderedWriting writing = new OrderedWriting(List.of(WritingEntry.linkPanel(), page("terrain/standard"),
+                block("obsidian"), page("feature/obelisks"), page("feature/obelisks")));
+        AgeGenerationPlan plan = AgeGenerationPlan.compile(writing, 56L, AgeGenerationProfiles.STANDARD,
+                AgeTraits.select(56L), registries);
+        var choices = AgeFeatureSelection.resolved(plan);
+        helper.assertValueEqual(choices.size(), 2, "Repeated Obelisks pages must remain separate");
+        helper.assertValueEqual(choices.getFirst().material(),
+                Optional.of(ResourceLocation.withDefaultNamespace("obsidian")),
+                "A preceding Block page must set the first obelisk material");
+        helper.assertTrue(choices.getLast().material().isPresent()
+                        && AgeFeatureSelection.materialError(choices.getLast()) == null,
+                "An unmodified Obelisks page must choose a valid material");
+        helper.assertValueEqual(AgeFeatureSelection.resolved(AgeGenerationPlan.load(plan.save())), choices,
+                "Obelisk materials and order must survive Age-plan reload");
+        for (String terrain : List.of("standard", "amplified", "island", "flat"))
+            helper.assertTrue(AgeFeatureSelection.error(id("obelisks"),
+                    AgeRuntimeProfiles.resolve(id(terrain)), registries) == null,
+                    "Obelisks should be valid on exposed " + terrain + " terrain");
+        for (String terrain : List.of("void", "cave"))
+            helper.assertTrue(AgeFeatureSelection.error(id("obelisks"),
+                    AgeRuntimeProfiles.resolve(id(terrain)), registries) != null,
+                    "Obelisks must reject " + terrain + " terrain without an exposed surface");
+        helper.succeed();
+    }
+
+    @GameTest(template = "empty")
+    public static void randomAgesOnlyChooseObelisksOnSupportedTerrain(GameTestHelper helper) {
+        var registries = helper.getLevel().registryAccess();
+        boolean selected = false;
+        for (long seed = 0; seed < 128; seed++) {
+            selected |= AgeFeatureSelection.randomChoices(seed,
+                    AgeRuntimeProfiles.resolve(id("standard")), registries).stream()
+                    .anyMatch(choice -> AgeFeatureSelection.obelisks(choice.id()));
+            for (String terrain : List.of("void", "cave"))
+                helper.assertTrue(AgeFeatureSelection.randomChoices(seed,
+                                AgeRuntimeProfiles.resolve(id(terrain)), registries).stream()
+                                .noneMatch(choice -> AgeFeatureSelection.obelisks(choice.id())),
+                        "Random " + terrain + " Ages must not gain Obelisks");
+        }
+        helper.assertTrue(selected, "Random surface Ages should be able to select Obelisks");
+        helper.succeed();
+    }
+
+    @GameTest(template = "empty")
+    public static void obeliskSitesAreSeededAndStayInsideTheirChunk(GameTestHelper helper) {
+        ChunkPos chunk = new ChunkPos(123, -45);
+        int selected = 0;
+        for (long seed = 0; seed < 2048; seed++) {
+            ObelisksFeature.Site site = ObelisksFeature.site(seed, chunk, 0);
+            helper.assertTrue(java.util.Objects.equals(ObelisksFeature.site(seed, chunk, 0), site),
+                    "An Age seed must reproduce the same obelisk site");
+            if (site == null) continue;
+            selected++;
+            helper.assertTrue(site.x() >= chunk.getMinBlockX() + 4
+                            && site.x() + 3 < chunk.getMaxBlockX(),
+                    "The full 4x4 plinth must remain inside its source chunk");
+            helper.assertTrue(site.z() >= chunk.getMinBlockZ() + 4
+                            && site.z() + 3 < chunk.getMaxBlockZ(),
+                    "The full 4x4 plinth must remain inside its source chunk");
+        }
+        helper.assertTrue(selected > 0 && selected < 64,
+                "The 1-in-128 roll should remain rare but reachable");
+        helper.succeed();
+    }
+
+    private static ResourceLocation id(String path) {
+        return ResourceLocation.fromNamespaceAndPath(Rivencraft.MOD_ID, path);
+    }
+
+    private static WritingEntry page(String path) {
+        return WritingEntry.symbol(new SymbolReference(id(path)));
+    }
+
+    private static WritingEntry block(String path) {
+        return WritingEntry.symbol(new SymbolReference(net.dnorberg.rivencraft.writing.BlockSymbolPages.symbolId(
+                ResourceLocation.withDefaultNamespace(path))));
+    }
+}

src/main/java/net/dnorberg/rivencraft/writing/WritingGrammar.java

@@ -78,7 +78,7 @@ public final class WritingGrammar {
             } else if (role == Role.FEATURE && pendingBlock != null) {
                 ResourceLocation feature = ((SymbolSemantics.ResourceValue) parsed.semantics().value()).id();
                 if (!Set.of("rocks", "surface_lakes", "deep_lakes", "lava_lakes",
-                                "floating_islands", "tendrils", "spheres", "spikes")
+                                "floating_islands", "tendrils", "spheres", "spikes", "obelisks")
                         .contains(feature.getPath()) || !feature.getNamespace().equals("rivencraft")) {
                     diagnostics.add(new Diagnostic(Code.MISPLACED_MODIFIER, pendingBlock.index(),
                             "This feature cannot consume a material page"));

src/main/resources/assets/rivencraft/blockstates/budding_crystal.json

@@ -0,0 +1 @@
+{"variants":{"":{"model":"rivencraft:block/budding_crystal"}}}

src/main/resources/assets/rivencraft/blockstates/crystal_block.json

@@ -0,0 +1 @@
+{"variants":{"":{"model":"rivencraft:block/crystal_block"}}}

src/main/resources/assets/rivencraft/blockstates/crystal_cluster.json

@@ -0,0 +1,56 @@
+{
+  "variants": {
+    "facing=down,waterlogged=false": {
+      "model": "rivencraft:block/crystal_cluster",
+      "x": 180
+    },
+    "facing=down,waterlogged=true": {
+      "model": "rivencraft:block/crystal_cluster",
+      "x": 180
+    },
+    "facing=up,waterlogged=false": {
+      "model": "rivencraft:block/crystal_cluster"
+    },
+    "facing=up,waterlogged=true": {
+      "model": "rivencraft:block/crystal_cluster"
+    },
+    "facing=north,waterlogged=false": {
+      "model": "rivencraft:block/crystal_cluster",
+      "x": 90
+    },
+    "facing=north,waterlogged=true": {
+      "model": "rivencraft:block/crystal_cluster",
+      "x": 90
+    },
+    "facing=south,waterlogged=false": {
+      "model": "rivencraft:block/crystal_cluster",
+      "x": 90,
+      "y": 180
+    },
+    "facing=south,waterlogged=true": {
+      "model": "rivencraft:block/crystal_cluster",
+      "x": 90,
+      "y": 180
+    },
+    "facing=east,waterlogged=false": {
+      "model": "rivencraft:block/crystal_cluster",
+      "x": 90,
+      "y": 90
+    },
+    "facing=east,waterlogged=true": {
+      "model": "rivencraft:block/crystal_cluster",
+      "x": 90,
+      "y": 90
+    },
+    "facing=west,waterlogged=false": {
+      "model": "rivencraft:block/crystal_cluster",
+      "x": 90,
+      "y": 270
+    },
+    "facing=west,waterlogged=true": {
+      "model": "rivencraft:block/crystal_cluster",
+      "x": 90,
+      "y": 270
+    }
+  }
+}

src/main/resources/assets/rivencraft/blockstates/large_crystal_bud.json

@@ -0,0 +1,56 @@
+{
+  "variants": {
+    "facing=down,waterlogged=false": {
+      "model": "rivencraft:block/large_crystal_bud",
+      "x": 180
+    },
+    "facing=down,waterlogged=true": {
+      "model": "rivencraft:block/large_crystal_bud",
+      "x": 180
+    },
+    "facing=up,waterlogged=false": {
+      "model": "rivencraft:block/large_crystal_bud"
+    },
+    "facing=up,waterlogged=true": {
+      "model": "rivencraft:block/large_crystal_bud"
+    },
+    "facing=north,waterlogged=false": {
+      "model": "rivencraft:block/large_crystal_bud",
+      "x": 90
+    },
+    "facing=north,waterlogged=true": {
+      "model": "rivencraft:block/large_crystal_bud",
+      "x": 90
+    },
+    "facing=south,waterlogged=false": {
+      "model": "rivencraft:block/large_crystal_bud",
+      "x": 90,
+      "y": 180
+    },
+    "facing=south,waterlogged=true": {
+      "model": "rivencraft:block/large_crystal_bud",
+      "x": 90,
+      "y": 180
+    },
+    "facing=east,waterlogged=false": {
+      "model": "rivencraft:block/large_crystal_bud",
+      "x": 90,
+      "y": 90
+    },
+    "facing=east,waterlogged=true": {
+      "model": "rivencraft:block/large_crystal_bud",
+      "x": 90,
+      "y": 90
+    },
+    "facing=west,waterlogged=false": {
+      "model": "rivencraft:block/large_crystal_bud",
+      "x": 90,
+      "y": 270
+    },
+    "facing=west,waterlogged=true": {
+      "model": "rivencraft:block/large_crystal_bud",
+      "x": 90,
+      "y": 270
+    }
+  }
+}

src/main/resources/assets/rivencraft/blockstates/medium_crystal_bud.json

@@ -0,0 +1,56 @@
+{
+  "variants": {
+    "facing=down,waterlogged=false": {
+      "model": "rivencraft:block/medium_crystal_bud",
+      "x": 180
+    },
+    "facing=down,waterlogged=true": {
+      "model": "rivencraft:block/medium_crystal_bud",
+      "x": 180
+    },
+    "facing=up,waterlogged=false": {
+      "model": "rivencraft:block/medium_crystal_bud"
+    },
+    "facing=up,waterlogged=true": {
+      "model": "rivencraft:block/medium_crystal_bud"
+    },
+    "facing=north,waterlogged=false": {
+      "model": "rivencraft:block/medium_crystal_bud",
+      "x": 90
+    },
+    "facing=north,waterlogged=true": {
+      "model": "rivencraft:block/medium_crystal_bud",
+      "x": 90
+    },
+    "facing=south,waterlogged=false": {
+      "model": "rivencraft:block/medium_crystal_bud",
+      "x": 90,
+      "y": 180
+    },
+    "facing=south,waterlogged=true": {
+      "model": "rivencraft:block/medium_crystal_bud",
+      "x": 90,
+      "y": 180
+    },
+    "facing=east,waterlogged=false": {
+      "model": "rivencraft:block/medium_crystal_bud",
+      "x": 90,
+      "y": 90
+    },
+    "facing=east,waterlogged=true": {
+      "model": "rivencraft:block/medium_crystal_bud",
+      "x": 90,
+      "y": 90
+    },
+    "facing=west,waterlogged=false": {
+      "model": "rivencraft:block/medium_crystal_bud",
+      "x": 90,
+      "y": 270
+    },
+    "facing=west,waterlogged=true": {
+      "model": "rivencraft:block/medium_crystal_bud",
+      "x": 90,
+      "y": 270
+    }
+  }
+}

src/main/resources/assets/rivencraft/blockstates/small_crystal_bud.json

@@ -0,0 +1,56 @@
+{
+  "variants": {
+    "facing=down,waterlogged=false": {
+      "model": "rivencraft:block/small_crystal_bud",
+      "x": 180
+    },
+    "facing=down,waterlogged=true": {
+      "model": "rivencraft:block/small_crystal_bud",
+      "x": 180
+    },
+    "facing=up,waterlogged=false": {
+      "model": "rivencraft:block/small_crystal_bud"
+    },
+    "facing=up,waterlogged=true": {
+      "model": "rivencraft:block/small_crystal_bud"
+    },
+    "facing=north,waterlogged=false": {
+      "model": "rivencraft:block/small_crystal_bud",
+      "x": 90
+    },
+    "facing=north,waterlogged=true": {
+      "model": "rivencraft:block/small_crystal_bud",
+      "x": 90
+    },
+    "facing=south,waterlogged=false": {
+      "model": "rivencraft:block/small_crystal_bud",
+      "x": 90,
+      "y": 180
+    },
+    "facing=south,waterlogged=true": {
+      "model": "rivencraft:block/small_crystal_bud",
+      "x": 90,
+      "y": 180
+    },
+    "facing=east,waterlogged=false": {
+      "model": "rivencraft:block/small_crystal_bud",
+      "x": 90,
+      "y": 90
+    },
+    "facing=east,waterlogged=true": {
+      "model": "rivencraft:block/small_crystal_bud",
+      "x": 90,
+      "y": 90
+    },
+    "facing=west,waterlogged=false": {
+      "model": "rivencraft:block/small_crystal_bud",
+      "x": 90,
+      "y": 270
+    },
+    "facing=west,waterlogged=true": {
+      "model": "rivencraft:block/small_crystal_bud",
+      "x": 90,
+      "y": 270
+    }
+  }
+}

src/main/resources/assets/rivencraft/lang/en_us.json

@@ -285,6 +285,17 @@
   "symbol.rivencraft.feature.trail_ruins.description": "Allow buried trail ruins in compatible surface biomes.",
   "symbol.rivencraft.feature.dense_ores": "Dense Ores",
   "symbol.rivencraft.feature.dense_ores.description": "Repeat compatible vanilla and modded ore placements once per page in this Age.",
+  "symbol.rivencraft.feature.obelisks": "Obelisks",
+  "symbol.rivencraft.feature.obelisks.description": "Add rare tall obelisks on exposed solid ground, with a random or selected block material.",
+  "symbol.rivencraft.feature.crystal_formations": "Crystal Formations",
+  "symbol.rivencraft.feature.crystal_formations.description": "Add blue crystal formations whose budding blocks grow harvestable clusters.",
+  "block.rivencraft.crystal_block": "Crystal Block",
+  "block.rivencraft.budding_crystal": "Budding Crystal",
+  "block.rivencraft.small_crystal_bud": "Small Crystal Bud",
+  "block.rivencraft.medium_crystal_bud": "Medium Crystal Bud",
+  "block.rivencraft.large_crystal_bud": "Large Crystal Bud",
+  "block.rivencraft.crystal_cluster": "Crystal Cluster",
+  "item.rivencraft.crystal_shard": "Crystal Shard",
   "symbol.rivencraft.feature.lava_lakes": "Small Lakes",
   "symbol.rivencraft.feature.lava_lakes.description": "Add small surface lakes using a random fluid, or specify one with a fluid page.",
   "generator.rivencraft.standard": "Standard",

src/main/resources/assets/rivencraft/models/block/budding_crystal.json

@@ -0,0 +1 @@
+{"parent":"minecraft:block/cube_all","textures":{"all":"rivencraft:block/budding_crystal"}}

src/main/resources/assets/rivencraft/models/block/crystal_block.json

@@ -0,0 +1 @@
+{"parent":"minecraft:block/cube_all","textures":{"all":"rivencraft:block/crystal_block"}}

src/main/resources/assets/rivencraft/models/block/crystal_cluster.json

@@ -0,0 +1 @@
+{"parent":"minecraft:block/cross","render_type":"minecraft:cutout","textures":{"cross":"rivencraft:block/crystal_cluster"}}

src/main/resources/assets/rivencraft/models/block/large_crystal_bud.json

@@ -0,0 +1 @@
+{"parent":"minecraft:block/cross","render_type":"minecraft:cutout","textures":{"cross":"rivencraft:block/large_crystal_bud"}}

src/main/resources/assets/rivencraft/models/block/medium_crystal_bud.json

@@ -0,0 +1 @@
+{"parent":"minecraft:block/cross","render_type":"minecraft:cutout","textures":{"cross":"rivencraft:block/medium_crystal_bud"}}

src/main/resources/assets/rivencraft/models/block/small_crystal_bud.json

@@ -0,0 +1 @@
+{"parent":"minecraft:block/cross","render_type":"minecraft:cutout","textures":{"cross":"rivencraft:block/small_crystal_bud"}}

src/main/resources/assets/rivencraft/models/item/budding_crystal.json

@@ -0,0 +1 @@
+{"parent":"rivencraft:block/budding_crystal"}

src/main/resources/assets/rivencraft/models/item/crystal_block.json

@@ -0,0 +1 @@
+{"parent":"rivencraft:block/crystal_block"}

src/main/resources/assets/rivencraft/models/item/crystal_cluster.json

@@ -0,0 +1 @@
+{"parent":"minecraft:item/generated","textures":{"layer0":"rivencraft:block/crystal_cluster"}}

src/main/resources/assets/rivencraft/models/item/crystal_shard.json

@@ -0,0 +1 @@
+{"parent":"minecraft:item/generated","textures":{"layer0":"rivencraft:item/crystal_shard"}}

src/main/resources/assets/rivencraft/models/item/large_crystal_bud.json

@@ -0,0 +1 @@
+{"parent":"minecraft:item/generated","textures":{"layer0":"rivencraft:block/large_crystal_bud"}}

src/main/resources/assets/rivencraft/models/item/medium_crystal_bud.json

@@ -0,0 +1 @@
+{"parent":"minecraft:item/generated","textures":{"layer0":"rivencraft:block/medium_crystal_bud"}}

src/main/resources/assets/rivencraft/models/item/small_crystal_bud.json

@@ -0,0 +1 @@
+{"parent":"minecraft:item/generated","textures":{"layer0":"rivencraft:block/small_crystal_bud"}}

src/main/resources/data/minecraft/tags/block/mineable/pickaxe.json

@@ -0,0 +1 @@
+{"replace":false,"values":["rivencraft:crystal_block","rivencraft:budding_crystal","rivencraft:small_crystal_bud","rivencraft:medium_crystal_bud","rivencraft:large_crystal_bud","rivencraft:crystal_cluster"]}

src/main/resources/data/minecraft/tags/item/cluster_max_harvestables.json

@@ -0,0 +1 @@
+{"replace":false,"values":["rivencraft:crystal_block","rivencraft:budding_crystal","rivencraft:small_crystal_bud","rivencraft:medium_crystal_bud","rivencraft:large_crystal_bud","rivencraft:crystal_cluster"]}

src/main/resources/data/rivencraft/loot_table/blocks/budding_crystal.json

@@ -0,0 +1,4 @@
+{
+  "type": "minecraft:block",
+  "random_sequence": "rivencraft:blocks/budding_crystal"
+}

src/main/resources/data/rivencraft/loot_table/blocks/crystal_block.json

@@ -0,0 +1,21 @@
+{
+  "type": "minecraft:block",
+  "pools": [
+    {
+      "bonus_rolls": 0.0,
+      "conditions": [
+        {
+          "condition": "minecraft:survives_explosion"
+        }
+      ],
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "rivencraft:crystal_block"
+        }
+      ],
+      "rolls": 1.0
+    }
+  ],
+  "random_sequence": "rivencraft:blocks/crystal_block"
+}

src/main/resources/data/rivencraft/loot_table/blocks/crystal_cluster.json

@@ -0,0 +1,81 @@
+{
+  "type": "minecraft:block",
+  "pools": [
+    {
+      "bonus_rolls": 0.0,
+      "entries": [
+        {
+          "type": "minecraft:alternatives",
+          "children": [
+            {
+              "type": "minecraft:item",
+              "conditions": [
+                {
+                  "condition": "minecraft:match_tool",
+                  "predicate": {
+                    "predicates": {
+                      "minecraft:enchantments": [
+                        {
+                          "enchantments": "minecraft:silk_touch",
+                          "levels": {
+                            "min": 1
+                          }
+                        }
+                      ]
+                    }
+                  }
+                }
+              ],
+              "name": "rivencraft:crystal_cluster"
+            },
+            {
+              "type": "minecraft:alternatives",
+              "children": [
+                {
+                  "type": "minecraft:item",
+                  "conditions": [
+                    {
+                      "condition": "minecraft:match_tool",
+                      "predicate": {
+                        "items": "#minecraft:cluster_max_harvestables"
+                      }
+                    }
+                  ],
+                  "functions": [
+                    {
+                      "add": false,
+                      "count": 4.0,
+                      "function": "minecraft:set_count"
+                    },
+                    {
+                      "enchantment": "minecraft:fortune",
+                      "formula": "minecraft:ore_drops",
+                      "function": "minecraft:apply_bonus"
+                    }
+                  ],
+                  "name": "rivencraft:crystal_shard"
+                },
+                {
+                  "type": "minecraft:item",
+                  "functions": [
+                    {
+                      "add": false,
+                      "count": 2.0,
+                      "function": "minecraft:set_count"
+                    },
+                    {
+                      "function": "minecraft:explosion_decay"
+                    }
+                  ],
+                  "name": "rivencraft:crystal_shard"
+                }
+              ]
+            }
+          ]
+        }
+      ],
+      "rolls": 1.0
+    }
+  ],
+  "random_sequence": "rivencraft:blocks/crystal_cluster"
+}

src/main/resources/data/rivencraft/loot_table/blocks/large_crystal_bud.json

@@ -0,0 +1,33 @@
+{
+  "type": "minecraft:block",
+  "pools": [
+    {
+      "bonus_rolls": 0.0,
+      "conditions": [
+        {
+          "condition": "minecraft:match_tool",
+          "predicate": {
+            "predicates": {
+              "minecraft:enchantments": [
+                {
+                  "enchantments": "minecraft:silk_touch",
+                  "levels": {
+                    "min": 1
+                  }
+                }
+              ]
+            }
+          }
+        }
+      ],
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "rivencraft:large_crystal_bud"
+        }
+      ],
+      "rolls": 1.0
+    }
+  ],
+  "random_sequence": "rivencraft:blocks/large_crystal_bud"
+}

src/main/resources/data/rivencraft/loot_table/blocks/medium_crystal_bud.json

@@ -0,0 +1,33 @@
+{
+  "type": "minecraft:block",
+  "pools": [
+    {
+      "bonus_rolls": 0.0,
+      "conditions": [
+        {
+          "condition": "minecraft:match_tool",
+          "predicate": {
+            "predicates": {
+              "minecraft:enchantments": [
+                {
+                  "enchantments": "minecraft:silk_touch",
+                  "levels": {
+                    "min": 1
+                  }
+                }
+              ]
+            }
+          }
+        }
+      ],
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "rivencraft:medium_crystal_bud"
+        }
+      ],
+      "rolls": 1.0
+    }
+  ],
+  "random_sequence": "rivencraft:blocks/medium_crystal_bud"
+}

src/main/resources/data/rivencraft/loot_table/blocks/small_crystal_bud.json

@@ -0,0 +1,33 @@
+{
+  "type": "minecraft:block",
+  "pools": [
+    {
+      "bonus_rolls": 0.0,
+      "conditions": [
+        {
+          "condition": "minecraft:match_tool",
+          "predicate": {
+            "predicates": {
+              "minecraft:enchantments": [
+                {
+                  "enchantments": "minecraft:silk_touch",
+                  "levels": {
+                    "min": 1
+                  }
+                }
+              ]
+            }
+          }
+        }
+      ],
+      "entries": [
+        {
+          "type": "minecraft:item",
+          "name": "rivencraft:small_crystal_bud"
+        }
+      ],
+      "rolls": 1.0
+    }
+  ],
+  "random_sequence": "rivencraft:blocks/small_crystal_bud"
+}

src/main/resources/data/rivencraft/recipe/crystal_block.json

@@ -0,0 +1,6 @@
+{
+  "type": "minecraft:crafting_shaped",
+  "pattern": ["SS", "SS"],
+  "key": {"S": {"item": "rivencraft:crystal_shard"}},
+  "result": {"id": "rivencraft:crystal_block", "count": 1}
+}

src/main/resources/data/rivencraft/rivencraft/symbols/feature/crystal_formations.json

@@ -0,0 +1,8 @@
+{
+  "schema_version": 2,
+  "name": "symbol.rivencraft.feature.crystal_formations",
+  "description": "symbol.rivencraft.feature.crystal_formations.description",
+  "category": "rivencraft:feature",
+  "semantics": { "role": "feature", "value": "rivencraft:crystal_formations" },
+  "poem": "Crystal Formation Growth Blue"
+}

src/main/resources/data/rivencraft/rivencraft/symbols/feature/obelisks.json

@@ -0,0 +1,8 @@
+{
+  "schema_version": 2,
+  "name": "symbol.rivencraft.feature.obelisks",
+  "description": "symbol.rivencraft.feature.obelisks.description",
+  "category": "rivencraft:feature",
+  "semantics": { "role": "feature", "value": "rivencraft:obelisks" },
+  "poem": "Civilization Structure Power Obelisk"
+}