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Formula:(Mn3+,Fe3+)(PO4)
Anhydrous normal phosphate, triphylite group, forms a series with
heterosite,
manganese-bearing mineral
Crystal System: Orthorhombic
Specific gravity: 3.2 to 3.4 measured, 3.69 calculated
Hardness: 4 to 4½
Streak: Light to medium purple, lighter than the colour of the massive mineral
Colour: Dark purple to purplish red
Solubility: Soluble in hydrochloric acid
Common impurities: Fe
Environments
Purpurite is a secondary mineral derived from oxidation and
leaching of primary manganese-iron phosphates, particularly
lithiophilite, in complex
granite pegmatites; the purpurite leaches
lithium out of its
site, leaving a vacancy, and oxidises divalent manganese Mn2+ to trivalent manganese Mn3+
(HOM, Mindat, Dana).
Rarely, purpurite is formed by reaction between bat guano and iron-manganese deposits resulting from seawater ingress
(HOM).
Associated minerals include lithiophilite,
sicklerite and many
secondary iron-manganese phosphates (HOM).
Localities
At the Emmons pegmatite, Greenwood, Oxford county, Maine, USA, purpurite forms in some pods as the major replacement of
lithiophilite. The Emmons pegmatite is an example of a highly evolved
boron-lithium-cesium-tantalum
enriched pegmatite
(R&M 94.6.513-514).
At the type locality, the Faires Mine, Kings Mountain, Gaston county, North Carolina, USA, purpurite occurs in oxidised
and leached primary
lithiophilite pods from a
granite pegmatite (Mindat).
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