Formula: ZnPb(SiO4)
Nesosilicate (insular SiO4 groups)
Crystal System: Orthorhombic
Specific gravity: 5.90 measured, 6.12 calculated
Hardness: 3
Streak: White
Colour: Colourless, white
Common impurities: Fe,Mn,Mg,Ca,H2O
Environments
Metamorphic environments
Hydrothermal environments
Larsenite is a very rare lead silicate found on fracture surfaces and
in cavities in massive metamorphosed
zinc deposits
(Webmin).
Localities
At Tsumeb, Namibia, larsenite has been found associated with
queitite and
alamosite
(HOM).
At the type locality, the Franklin Mine, Franklin, Franklin Mining District, Sussex county, New Jersey, USA,
larsenite is a very
rare secondary nesosilicate in vugs usually associated with
esperite and clinohedrite.
The assemblage is composed
of lead-rich silicates which are the result of hydrothermal alteration cutting
and replacing coarse, massive
willemite-franklinite ore in
a stratiform,
Precambrian (more than 543 million years old)
zinc-manganese-iron
deposit
(Mindat, HOM).
Associated minerals include willemite,
clinohedrite,
esperite, hardystonite,
hodgkinsonite, andradite,
calcite, smithsonite,
zincite, franklinite,
roeblingite, garnet,
zincite, calcite,
bementite and neotocite. Larsenite is the
last mineral to crystallise in a few cavities
(AM 13.142-144).
Larsenite is far less abundant than esperite and in most of
the specimens the two are
not associated but in two cases crystals of larsenite occur in cavities in the walls of which
esperite is present
(AM 13.334-340).
Alteration
Larsenite melts incongruently at 1,000oC and 1 atmosphere pressure to
willemite
and liquid lead silicate; under hydrothermal conditions larsenite becomes unstable between 550oC
and 650oC
(AM 52.1077-1084).
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