Hemimorphite

Hemimorphite
General
CategorySorosilicates
Formula
(repeating unit)
Zn4Si2O7(OH)2·H2O
IMA symbolHmp[1]
Strunz classification9.BD.10
Crystal systemOrthorhombic
Crystal classPyramidal (mm2)
H-M symbol: (mm2)
Space groupImm2
Unit cella = 8.367(5), b = 10.73
c = 5.155(3) [Å]; Z = 2
Identification
ColorWhite, grey
Crystal habitPolar crystals, with different or hemimorphic ends. Also coxcomb masses, mammillary, stalactitic, or massive
TwinningRare on {001}
CleavagePerfect on {110}, poor on {101}, {001} rare
FractureUneven to conchoidal
TenacityBrittle
Mohs scale hardness4.5–5
LusterVitreous, adamantine, rarely silky
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity3.516–3.525
Optical propertiesBiaxial (+)
Refractive indexnα = 1.614 nβ = 1.617 nγ = 1.636
Birefringenceδ = 0.022
2V angleMeasured: 46°, calculated: 44°
SolubilitySoluble 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.

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Handbook of Mineralogy
  3. ^ Webmineral
  4. ^ Mindat.org