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Formula:Fe3+(PO4)
Anhydrous normal phosphate, triphylite group, forms a series with
purpurite and with triphylite
(Dana).
Crystal System: Orthorhombic
Specific gravity: 3.40 measured, 3.67 calculated
Hardness: 4 to 4½
Streak: Pale purple
Colour: Usually purple-black, also deep rose to reddish purple, especially when treated in a strong acid solution
Solubility: Readily soluble in hydrochloric acid
Common impurities: Mn
Environments
Heterosite is a secondary mineral in the oxidised zone of
complex granite pegmatites, formed by oxidation of iron and or manganese
with the simultaneous leaching of lithium from
primary phosphates,
usually lithiophilite or
triphylite (Webmin, Mindat, HOM).
Associated minerals include muscovite,
quartz, triphylite,
ferrisicklerite and many
secondary iron-manganese phosphates (Mindat, HOM).
At the type locality, Les Hureaux, Saint-Sylvestre, Haute-Vienne, Nouvelle-Aquitaine, France, heterosite occurs in a
granite pegmatite (Mindat).
At the Chickering Mine, Walpole, Cheshire County, New Hampshire, USA, heterosite is a
secondary mineral resulting
from the oxidation of triphylite, with
ferrisicklerite as an intermediate phase. It is most commonly
associated with quartz, albite,
muscovite, siderite, and
ferrisicklerite
(R&M 90.5.418).
At the Keyes Mica Quarries, Orange, Grafton County, New Hampshire, USA, the
pegmatites are beryl-type
rare-element (RE) pegmatites.
The Number 1 mine exposed a pegmatite that shows the most
complex zonation and diverse mineralogy of any of the Keyes
pegmatites. Six zones are distinguished, as follows, proceeding
inward from the margins of the pegmatite:
(1) quartz-muscovite-plagioclase
border zone, 2.5 to 30.5 cm thick
(2) plagioclase-quartz-muscovite
wall zone, 0.3 to 2.4 metres thick
(3) plagioclase-quartz-perthite-biotite
outer intermediate zone, 0.3 to 5.2 metres thick, with lesser muscovite
(4) quartz-plagioclase-muscovite
middle intermediate zone, 15.2 to 61.0 cm thick
(5) perthite-quartz inner intermediate zone, 0.9 to 4.6 meters thick
(6) quartz core, 1.5 to 3.0 metres across
The inner and outer intermediate zones contained perthite crystals up to
1.2 meters in size that were altered to vuggy
albite-muscovite with
fluorapatite crystals. This unit presumably was the source of the
albite, muscovite,
fluorapatite, quartz and other
crystallised minerals found in pieces of vuggy albite
rock on the dumps next to the mine.
The middle intermediate zone produced sheet mica with accessory minerals including
tourmaline, graftonite,
triphylite, vivianite,
pyrite, pyrrhotite, and
beryl crystals to 30.5 cm long and 12.7 cm across.
Heterosite has been found with albite at the Keyes No. 1 mine. It was
derived from the alteration of triphylite and in some specimens is associated
with other phosphates. It occurs as friable masses to at least 6 cm, and shows the typical purple colour on weathered
surfaces. A specimen has been found that is an apparent pseudomorph of
heterosite after a rough triphylite crystal on a densely fractured
quartz matrix
(R&M 97.4.318).
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