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Formula: CaMg(AsO4)F
Anhydrous arsenate,
tilasite group
Crystal System: Monoclinic
Specific gravity: 3.77 measured, 3.80 calculated
Hardness: 5
Colour: Light gray, violet-gray, pinkish red (Långban); olive-green, apple-green (India);
colourless or pale green in transmitted light.
Solubility: Readily soluble in hydrochloric and nitric acid
Environments:
Tilasite occurs typically in metamorphosed manganese or
zinc deposits containing arsenic.
At Kajlidongri, India, tilasite occurs with spessartine,
braunite, baryte,
and quartz (HOM).
At the type locality, Långban, Filipstad, Värmland, Sweden, tilasite occurs in
dolomitic
limestone, (Dana) associated with
pyrochroite,
pyroaurite,
hematite,
hausmannite,
dixenite,
calcite, berzeliite,
manganberzeliite,
baryte, manganoan
diopside, svabite,
bergslagite and
allactite
(Mindat).
At Sterling Hill, New Jersey, USA, tilasite is associated with
friedelite,
willemite and baryte
(HOM).
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