Crystal Mahagony Obsidian

Category

Volcanic glass

Formula
(repeating unit)

70–75% SiO₂,
plus MgO, Fe₃O₄

Identification

Color

Deep black or blackish green

Fracture

Conchoidal

Mohs scalehardness

5–6^[1]

Luster

Vitreous

Specific gravity

~2.4^[2]

Optical properties

Translucent

References

^[3]