Port authored Obelisks age feature (#56)

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/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 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. Fissures, crystals, 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).

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=0.4.17.0
 immersive_portals_version=6.0.7
 terrablender_version=4.1.0.8
 serene_seasons_version_id=B6nTjh4b

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

@@ -27,7 +27,8 @@ 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;
@@ -121,6 +122,8 @@ 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 +139,8 @@ 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;
             }
@@ -208,6 +212,11 @@ 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 +307,13 @@ 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");
         helper.assertTrue(PageItem.bundledCreativeSymbols().containsAll(pages),
                 "Supported feature pages must appear in the creative and JEI symbol feed");
         for (String path : pages) {
@@ -72,6 +72,7 @@ public final class FeatureWritingGameTests {
                     || AgeFeatureSelection.skylands(choice.id())
                     || AgeFeatureSelection.spheres(choice.id())
                     || AgeFeatureSelection.spikes(choice.id())
+                    || AgeFeatureSelection.obelisks(choice.id())
                     || choice.id().equals(AgeDenseOres.ID)) continue;
             var placement = AgeFeatureSelection.placedFeature(choice.id());
             helper.assertTrue(registries.lookupOrThrow(Registries.PLACED_FEATURE)
@@ -419,7 +420,8 @@ 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/world/AgeFeatureChunkGenerator.java

@@ -162,6 +162,7 @@ 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;
         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 +171,10 @@ 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(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/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/lang/en_us.json

@@ -285,6 +285,8 @@
   "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.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/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"
+}