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


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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