Hydrozincite

Hydrozincite, also known as zinc bloom or marionite, is a white carbonate mineral consisting of Zn₅(CO₃)₂(OH)₆. It is usually found in massive rather than crystalline form.

Hydrozincite
General
Category	Carbonate mineral
Formula (repeating unit)	Zn5(CO3)2(OH)6
IMA symbol	Hznc[1]
Strunz classification	5.BA.15
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/m
Unit cell	a = 13.58 Å, b = 6.28 Å, c = 5.41 Å; β = 95.51°, Z = 2
Identification
Color	White to grey, stained pale pink, or pale yellow or brown; colourless in transmitted light.
Crystal habit	Lathlike or bladed crystals uncommon, in fibrous, stalactitic, reniform, pisolitic aggregates; also earthy, chalky, massive
Twinning	Contact twinning on {100}
Cleavage	Perfect on {100}
Fracture	Irregular/uneven
Tenacity	Very brittle
Mohs scale hardness	2 - 2+1⁄2
Luster	Silky, pearly, dull, earthy
Streak	White
Diaphaneity	Transparent, translucent
Specific gravity	3.5 - 4
Optical properties	Biaxial (-)
Refractive index	nα = 1.630 nβ = 1.642 nγ = 1.750
Birefringence	δ = 0.120
2V angle	Measured: 40° , calculated: 40°
Dispersion	relatively strong
Ultraviolet fluorescence	Fluoresces pale blue to lilac under UV
Solubility	Readily soluble in acids.
References	[2][3][4]

It occurs as an oxidation product of zinc ores and as post mine incrustations. It occurs associated with smithsonite, hemimorphite, willemite, cerussite, aurichalcite, calcite and limonite.[2]

It was first described in 1853 for an occurrence in Bad Bleiberg, Carinthia, Austria and named for its chemical content.[3]