Obsidian

Obsidian is a type of block found in the update 0.28_01. It's color is dark purple and dark blue, it's sort of like the bedrock, but its main color is purple.

Obsidian is never to be found in a generated map, though it was originally thought that obsidian was cooled lava, which could emerge if it collides with water. Obsidian is a great block to use for art, especially when you use a lot of black.