Hemimorphite

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Hemimorphite" – news · newspapers · books · scholar · JSTOR (September 2023) (Learn how and when to remove this message)

This article includes a list of general references, but it lacks sufficient corresponding inline citations. Please help to improve this article by introducing more precise citations. (March 2021) (Learn how and when to remove this message)

Hemimorphite
General
Category	Sorosilicates
Formula (repeating unit)	Zn4Si2O7(OH)2·H2O
IMA symbol	Hmp[1]
Strunz classification	9.BD.10
Crystal system	Orthorhombic
Crystal class	Pyramidal (mm2) H-M symbol: (mm2)
Space group	Imm2
Unit cell	a = 8.367(5), b = 10.73 c = 5.155(3) [Å]; Z = 2
Identification
Color	White, grey
Crystal 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 scale hardness	4.5–5
Luster	Vitreous, adamantine, rarely silky
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	3.516–3.525
Optical properties	Biaxial (+)
Refractive index	nα = 1.614 nβ = 1.617 nγ = 1.636
Birefringence	δ = 0.022
2V angle	Measured: 46°, calculated: 44°
Solubility	Soluble in acid
References	[2][3][4]

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.

The silicate was the rarer of the two and was named hemimorphite because of the hemimorph development of its crystals. This unusual form, which is typical of only a few minerals, means that the crystals are terminated by dissimilar faces. Hemimorphite most commonly forms crystalline crusts and layers, also massive, granular, rounded and reniform aggregates, concentrically striated, or finely needle-shaped, fibrous or stalactitic, and rarely fan-shaped clusters of crystals.

Some specimens show strong green fluorescence in shortwave ultraviolet light (253.7 nm) and weak light pink fluorescence in longwave UV.