A111 Obsidian

Obsidian has been used since the Stone Age for tools, weapons and as an ornamental material. It is used in modern times for scalpel blades. Obsidian is formed by the rapid cooling of viscous lava due to volcanic explosions. It consists of the same minerals as granite but cools so quickly that they do not have time to crystallize. Obsidian has a glassy luster and is usually black or very dark green, but it can also be found in an almost colorless form. Measures 22x16mm.