Laurionite

Laurionite
Laurionite crystals in a vug from the Laurium district of Greece
General
Category	Halide minerals
Formula (repeating unit)	PbCl(OH)
Strunz classification	3.DC.05
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pnma
Unit cell	a = 7.111, b = 9.6987 c = 4.0203 [Å]; Z = 4
Identification
Color	Colorless, white
Crystal habit	Elongated tabular prismatic crystals
Cleavage	Distinct on {101}
Tenacity	Flexible
Mohs scale hardness	3 - 3.5
Luster	Adamantine, pearly
Streak	White
Diaphaneity	Transparent
Specific gravity	6.241
Optical properties	Biaxial (-)
Refractive index	nα = 2.077 nβ = 2.116 nγ = 2.158
Birefringence	δ = 0.081
2V angle	Measured: 70°
Solubility	Sleight in cold water
References

Laurionite (PbCl(OH)) is a lead halide mineral. It forms colorless to white crystals in the orthorhombic crystal system and is dimorphous with paralaurionite, both members of the matlockite group.

It was first described in 1887 for an occurrence in the Laurium District, Attica, Greece and named after the town Laurium. It occurs as an oxidation product in lead ore deposits, and is also produced on lead-bearing slag by reaction with saline solutions. It occurs associated with paralaurionite, penfieldite, fiedlerite, phosgenite, cerussite and anglesite.