Paralaurionite

Paralaurionite
Platey clear paralaurionite crystals from slag in the Thorikos area, Lavrion, Attica, Greece
General
Category	Halide mineral
Formula (repeating unit)	PbCl(OH)
Strunz classification	3.DC.05
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	C2/m
Unit cell	a = 10.865(4) Å, b = 4.006(2) Å, c = 7.233(3) Å; β = 117.24(4)°; Z = 4
Identification
Color	Colorless, white, pale greenish, yellowish, yellow-orange, rarely violet
Crystal habit	Elongated tabular crystals
Twinning	Contact twinning on {100}
Cleavage	Perfect on {001}
Tenacity	Flexible, non-elastic
Mohs scale hardness	3
Luster	Subadamantine
Diaphaneity	Transparent to translucent
Specific gravity	6.05–6.15
Optical properties	Biaxial (-)
Refractive index	nα = 2.050 nβ = 2.150 nγ = 2.200
Birefringence	δ = 0.150
Pleochroism	Visible
References

Paralaurionite is a colorless mineral consisting of a basic lead chloride PbCl(OH) that is dimorphous with laurionite. It is a member of the matlockite group. The name is derived from para-, the Greek for "near", and laurionite, because of its polymorphic relationship to it. Bright, yellow tips of thorikosite can form on paralaurionite crystals and paralaurionite may also be intergrown with mendipite.

It was first described in 1899 for an occurrence in slag in Laurium, Attica, Greece. In 1952 an occurrences of it was reported from the Mammoth Mine, Arizona.

It occurs in lead bearing slag which has been exposed to seawater. It also occurs in polymetallic ore deposits. It occurs associated with laurionite, penfieldite, fiedlerite, phosgenite in slag deposits; and with leadhillite, matlockite, cerussite, hydrocerussite, diaboleite and wherryite in the Mammoth mine location.