Willemite

Formula: Zn2SiO4

Origin of name: for William I (1772-1843), King of the Netherlands (1813-1840)

 

Crystal system: Hexagonal

Crystal class: 3

Twinning:

Unit cell: a = 13.94 Å, c = 9.31 Å

 

Colour: Colourless, white, green, yellow, red, brown, gray

Diaphaneity: Transparent to translucent to opaque

Luster: Vitreous to resinous

Habit: Crystals stout to long slender prismatic, hexagonal, disseminated grains, massive, compact or fibrous

Hardness: 5.5

Specific gravity: 3.89 to 4.19

Cleavage: 2; {0001} and {11-20} poor

Tenacity: Conchoidal to uneven fracture, brittle

Streak: White

 

Synonyms/varieties: Troostite (red-brown variety)

 

Comments: Often fluoresces intense yellowish green SW-UV, often strongly phosphorescent

 

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