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]
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