Black Sand
From The Blockheads Wiki
Black Sand is a mottled charcoal colored block.
Where Found
A Blockhead can find sand underneath some bodies of water. It is far less common than normal sand but tends to appear in streaks.
Gathering
It's best harvested using a spade, although there is no loss associated with using anything else. A gold spade will produce occasional bonuses.
Crafting
Black Sand can be processed in a Kiln to make Black Glass. It is also needed to make a Magnet.