Silly me, prismarine isn't an ore.

src/main/java/com/gmail/nossr50/util/BlockUtils.java

@@ -174,6 +174,7 @@ public final class BlockUtils {
             case STAINED_CLAY:
             case STONE:
             case RED_SANDSTONE:
+            case PRISMARINE:
                 return true;
 
             default:

src/main/java/com/gmail/nossr50/util/MaterialUtils.java

@@ -18,7 +18,6 @@ public final class MaterialUtils {
             case QUARTZ_ORE:
             case REDSTONE_ORE:
             case EMERALD_ORE:
-            case PRISMARINE:
                 return true;
             default:
                 return mcMMO.getModManager().isCustomOre(data);