Variety/Type Of: Boron silicate

Color: Black is the most common color. Also occurs in blue, green, yellow, pink, red, orange, purple, brown, and colorless. Single crystals are often color-zoned.

Streak: White when softer than the streak plate. Colorless when harder than the streak plate.

Luster: Vitreous

Cleavage: Indistinct

Hardness: 7 to 7.5

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