Basalt
From The Blockheads Wiki
Template:Block Infobox Basalt is a special type of block that can only be created without a crafting surface.
Appearance
Basalt is generally black liberally covered with white to gray speckles.
Where Found
Unlike other blocks, basalt is not spawned as part of a world. Instead, it is created when water is placed on top of magma near the center of the world. It must then be mined.
Note that water occurring naturally (i.e. as part of world generation) on top of magma does not form basalt.
Uses
Basalt is useful in construction. It has no known use in crafting.