diff --git a/index.js b/index.js
index fe2e14f..47889ac 100644
--- a/index.js
+++ b/index.js
@@ -367,10 +367,63 @@ function castRay(world, origin, direction, maxDistance) {
     }
 }
 
+function viewDirection(params) {
+    const dir = [0, 0, -1, 1.0];
+    const camori = params.camera.orientation;
+    const ori = se3.inverse(se3.rotxyz(-camori[0], -camori[1], -camori[2]));
+    return se3.apply(ori, dir).slice(0, 3);
+}
+
+function destroySelectedBlock(params) {
+    const hit = castRay(params.world, params.camera.position, viewDirection(params), params.blockSelectDistance);
+    if (hit === undefined || hit.block.type === BlockType.UNDEFINED) {
+        return;
+    }
+
+    const trimFaces = chunk => {
+        chunk.faces = chunk.faces.filter(({blockIndex}) => chunk.data[blockIndex] !== BlockType.AIR);
+    }
+
+    hit.block.chunk.data[hit.block.blockIndex] = BlockType.AIR;
+    if (hit.block.chunk.buffer !== undefined) {
+        hit.block.chunk.buffer.delete();
+        delete hit.block.chunk.buffer;
+    }
+    trimFaces(hit.block.chunk);
+
+    const [bx, by, bz] = hit.block.centerPosition;
+
+    const neighbors = [
+        { block: blockLookup(params.world, bx - 1, by, bz), dir: '+x' },
+        { block: blockLookup(params.world, bx + 1, by, bz), dir: '-x' },
+        { block: blockLookup(params.world, bx, by - 1, bz), dir: '+y' },
+        { block: blockLookup(params.world, bx, by + 1, bz), dir: '-y' },
+        { block: blockLookup(params.world, bx, by, bz - 1), dir: '+z' },
+        { block: blockLookup(params.world, bx, by, bz + 1), dir: '-z' },
+    ];
+
+    neighbors
+        .filter(({ block }) => block.type !== BlockType.AIR &&
+            block.type !== BlockType.UNDEFINED)
+        .forEach(({ block, dir }) => {
+            const blocki = Math.floor(block.blockIndex / (16 * 256));
+            const blockj = Math.floor(block.blockIndex / 256) - 16 * blocki;
+            const blockk = block.blockIndex % 256;
+
+            block.chunk.faces.push(createChunkFace(block, dir));
+            trimFaces(block.chunk);
+
+            if (block.chunk.buffer !== undefined) {
+                block.chunk.buffer.delete();
+                delete block.chunk.buffer;
+            }
+        });
+}
+
 function markBlock(world, cameraPosition, direction, maxDistance) {
     const hit = castRay(world, cameraPosition, direction, maxDistance);
 
-    if (hit === undefined) {
+    if (hit === undefined || hit.block.type === BlockType.UNDEFINED) {
         return;
     }
 
diff --git a/world.js b/world.js
index 9bc25f2..c405c1e 100644
--- a/world.js
+++ b/world.js
@@ -1,6 +1,7 @@
 import { makeBufferFromFaces, makeFace} from "./geometry";
 
 export const BlockType = {
+    UNDEFINED: 0,
     AIR: 1,
     DIRT: 2,
     GRASS: 3,
@@ -87,6 +88,11 @@ function makeChunk(z, x) {
 }
 
 export function blockLookup(world, x, y, z) {
+    if (y < 0.5 || z > 255.5) {
+        return {
+            type: BlockType.UNDEFINED,
+        }
+    }
     const midx = x + 0.5;
     const midy = y + 0.5;
     const midz = z + 0.5;
@@ -97,8 +103,7 @@ export function blockLookup(world, x, y, z) {
     const chunk = world.chunkMap.get(chunki, chunkj);
     if (chunk === undefined) {
         return {
-            type: BlockType.STONE,
-            centerPosition: [x, y, z],
+            type: BlockType.UNDEFINED,
         };
     }
 
@@ -121,6 +126,9 @@ function makeChunkBuffer(gl, data, z0, x0, blockLookup) {
         if (i < 0 || j < 0 || i > 15 || j > 15) {
             return blockLookup(i, j, k);
         }
+        if (k < 0 || k > 255) {
+            return BlockType.UNDEFINED;
+        }
         return data[256*(16*i + j) + k];
     };
     const sideNeighbors = (i, j, k) =>