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Formula:
Ca6Al2(SO4)2B(OH)4(OH,O)12.26H2O
Compound sulphate, ettringite group
Crystal System: Trigonal
Specific gravity: 1.77 measured, 1.79 calculated
Hardness: 2½
Streak: White
Colour: Colourless, white
Environments
Metamorphic environments
Hydrothermal environments
Charlesite is a very rare mineral.
Localities
At the type locality, the Franklin mine, Franklin, Franklin Mining District, Sussex county, New Jersey, USA, charlesite occurs in a
metamorphosed stratiform carbonate hosted zinc silicate and oxide deposit (Mindat).
Three samples from the type locality have been described in some detail. They have similar mineralogy, but indicate somewhat different
parageneses.
(1) For the first sample the ore consists of franklinite and
willemite with minor andradite and moderately abundant
mica, likely of phlogopite -
hendricksite composition. This primary assemblage is unevenly coated with a layer of
grossular which is coated, in turn, with a fine-grained impure mixture of a
ganophyllite-like mineral of unknown composition. Subsequent crystallisation produced a
thick druse of ganophyllite in crystals up to 2.0 mm, intergrown with second-generation
willemite and minor rhodonite. These three minerals
are unevenly coated with a manganese-bearing chlorite and
pectolite. Continued crystallisation resulted in the growth of charlesite crystals up
to 6mm, which appear to have formed contemporaneously with clinohedrite. These minerals were
followed by very small crystals of pectolite and
xonotlite.
(2) For the second sample the assemblage consists of willemite and
franklinite ore coated with a second generation of
willemite crystals to 2 cm. Some willemite has been
partially dissolved, leaving vugs and molds formed of granular grossular which is coated with
hancockite crystals. Charlesite crystals occur in vugs among the
willemite crystals and also filling cracks in fractured
willemite. These willemite crystals are coated with
a manganese-bearing chlorite and, in turn, by prehnite.
Some interstices among these coated crystals are filled with granular clinohedrite. The
entire assemblage is covered by a druse of granular datolite, followed by massive
roeblingite.
(3) The third sample is the type specimen. The ore is franklinite with very minor
willemite, which is encrusted with a layer of recrystallized
datolite, axinite-(Mn),
prehnite and hancockite. This layer is, in turn,
coated with ganophyllite, followed by a layer of extremely fine-grained manganese-bearing
chlorite. Subsequent crystallisation gave rise to prehnite,
followed by sparse baryte and, in turn, abundant
clinohedrite and charlesite. In this assemblage, the charlesite crystals in
some cases are cavernous and partially dissolved.
Although these parageneses have some minerals in common, the diversity suggests some degree of spatial separation of the occurrences
(AM 68.1033-1037).
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