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Formula: Al(PO4).2H2O
Hydrated normal phosphate, variscite group
Crystal System: Orthorhombic
Specific gravity: 2.57 to 2.61 measured, 2.59 calculated
Hardness: 4½
Streak: White
Colour: Pale to emerald-green, bluish green, colourless to white, pale shades of brown or yellow,
rarely red; Colourless to pale green in transmitted light.
Solubility: Insoluble in hydrochloric acid. Soluble in alkalis.
Common impurities: Fe,As
Environments:
Variscite is typically deposited under surface conditions in cavities or
breccias when phosphatic
meteoric waters act on aluminous rocks. Associated minerals include
wavellite,
crandallite,
metavariscite,
apatite and
chalcedony
(Dana).
The rare secondary mineral
gordonite
is sometimes formed from the alteration of variscite in nodules in
limestone.
(Dana).
Localities
At the phosphate deposits of the Mount Lofty ranges, South Australia, although uncommon, variscite has been
found in several
associations. At the Moculta quarry it is associated with opal and
jarosite, and in cavities lined with
apatite
and associated with wavellite,
beraunite
and cyrilovite. It has also been found associated with
cacoxenite, leucophosphite
and
pyrite, and with wavellite and
minyulite.
At Tom's quarry variscite is associated with fluellite,
leucophosphite, cacoxenite,
wavellite and meurigite-Na in
goethite-rich rocks. It has been found perched on
minyulite and coating
fluorapatite,
fluellite and minyulite. In one
part of the
quarry nodules of variscite have been collected in a mudstone
containing
mica, tourmaline and
rutile, and the variscite is partially altered to
crandallite and associated with
leucophosphite and
childrenite.
At the Fairview workings variscite is associated with fluellite and
at St John's quarry
with leucophosphite and
cacoxenite
(AJM 17.1.26 ).
At the Mount Deverell variscite deposit, Milgun Station, Western Australia,
variscite
occurs as narrow veins that crosscut siltstone and
mudstone as well as veins of
quartz. The
veins commonly have rims to 3 mm wide where the variscite has been partially
altered to
crandallite, foggite,
quartz and/or wardite. The veins may
be laterally
altered and replaced by secondary minerals such as montgomeryite,
hydroxylapatite, strengite
and
leucophosphite. Variscite also forms
pseudomorphs after
pyrite. The variscite deposits are hosted by marine sedimentary rocks
(AJM 20.2.31).
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