Paralaurionite

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.^[6] The name is derived from para-, the Greek for "near", and laurionite, because of its polymorphic relationship to it.^[4] Bright, yellow tips of thorikosite can form on paralaurionite crystals and paralaurionite may also be intergrown with mendipite.^[7][8]

Paralaurionite
Platey clear paralaurionite crystals from slag in the Thorikos area, Lavrion, Attica, Greece
General
Category	Halide mineral
Formula	PbCl(OH)
IMA symbol	Plri[1]
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	[2][3][4][5]

Occurrence

It was first described in 1899 for an occurrence in slag in Laurium, Attica, Greece.^[3] In 1952 an occurrences of it was reported from the Mammoth Mine, Arizona.^[9]

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.^[3]