Nesosilicate (insular SiO4 groups)
Specific gravity: 5.90
Colour: Colourless, white
Common impurities: Fe,Mn,Mg,Ca,H2O
Larsenite is a very rare lead silicate found on fracture surfaces and in cavities in massive metamorphosed
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 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).
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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