Hemimorphite
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Hemimorphite is the chemical compound Zn₄(OH)₂·H₂O, a component of mineral calamine. It is a silicate mineral which, together with smithsonite, has been historically mined from the upper parts of zinc and lead ores. Both compounds were originally... Wikipedia
Crystal system: Orthorhombic
Color: White, grey
Crystal class: Pyramidal (mm2); H-M symbol: (mm2)
Crystal habit: Polar crystals, with different or hemimorphic ends. Also coxcomb masses, mammillary, stalactitic, or massive
Formula (repeating unit): Zn4Si2O7(OH)2·H2O
Fracture: Uneven to conchoidal
Luster: Vitreous, adamantine, rarely silky