Obsidiana Sink.

Obsidian is a black volcanic glass created by rapidly cooling volcanic lava. The obsidian, or Lapilli, used came out last year from the Cumbre Vieja volcano in the Canary Islands.
It is an extremely brittle and abrasive igneous rock, which is why it is difficult to work, very light, so we can make it float, and with a very dark and deep color typical of translucent crystals.