Obsidian

Obsidian is a black volcanic glass.  It forms from super-cooled lava. It has been used for some of the earliest tools of humankind.

Type

Rock

Chemical Formula

Non-uniform mixture 70–75% SiO2, with MgO, Fe3O4

Streak

White

Mohs Hardness

5

Color

Usually Black, but highly variable

Luster

Vitreous

Fracture

conchoidal

Description

Obsidian is a black volcanic glass.  It forms from super-cooled lava. It has been used for some of the earliest tools of humankind.

Uses

Obsidian is currently used for ornamental purposes, and researchers are investigating the use of obsidian for surgical scalpels in the medical industry.