hemimorphite

{{Infobox mineral | name = Hemimorphite | category = Sorosilicates | image = Hemimorphite - Mapimi, Durango, Mexico.jpg | imagesize = 260px | caption = | formula = Zn4Si2O7(OH)2·H2O | IMAsymbol = Hmp | molweight = | strunz = 9.BD.10 | system = Orthorhombic | class = Pyramidal (mm2) H-M symbol: (mm2) | symmetry = Imm2 | unit cell = a = 8.367(5), b = 10.73 c = 5.155(3) [Å]; Z = 2 | colour = White, grey, blue | habit = Polar crystals, with different or hemimorphic ends. Also coxcomb masses, mammillary, stalactitic, or massive | twinning = Rare on {001} | cleavage = Perfect on {110}, poor on {101}, {001} rare | fracture = Uneven to conchoidal | tenacity = Brittle | mohs = 4.5–5 | luster = Vitreous, adamantine, rarely silky | refractive = nα = 1.614 nβ = 1.617 nγ = 1.636 | opticalprop = Biaxial (+) | birefringence = δ = 0.022 | pleochroism = | 2V = Measured: 46°, calculated: 44° | streak = White | gravity = 3.516–3.525 | density = | melt = | fusibility = | diagnostic = | solubility = Soluble in acid | diaphaneity = Transparent to translucent | other = | references = }}

Hemimorphite is the chemical compound Zn4(Si2O7)(OH)2·H2O, a component of mineral calamine. It is a silicate mineral which, together with smithsonite (ZnCO3), has been historically mined from the upper parts of zinc and lead ores. Both compounds were originally believed to be the same mineral and classified as calamine. In the second half of the 18th century, it was discovered that these two different compounds were both present in calamine. They closely resemble one another.