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Formula: Fe2+3Al4(PO4)4(OH)6.2H2O
Hydrated phosphate containing hydroxyl, forms a series with souzalite
Crystal System: Triclinic
Specific gravity: 3.10 to 3.13 measured, 3.11 calculated
Hardness: 4 to 5
Streak: Pale green
Colour: Blue green to dark green
Environments
Plutonic igneous environments
Pegmatites
Gormanite forms as a late stage mineralisation in granite
pegmatites
(Mindat).
Localities
There are two co-type localities, Big Fish River, and Rapid Creek, both in the Dawson mining district, Yukon, Canada.
Gormanite-souzalite crystals are very common here, seen in thin
sections of the phosphatic ironstone beds as green, elongate crystals
in radial aggregates, and in open fractures as elongate, blade-like crystals. In many fractures
gormanite-souzalite crystals constitute the only phosphate mineral
and are generally accompanied by quartz and
siderite. Elsewhere,
gormanite-souzalite has been found in close association with
ludlamite, arrojadite,
kryzhanovskite and oxidised
vivianite. In places, needles of
gormanite-souzalite are included in
quartz, giving the quartz crystals a
green color. The absence of any sign of metamorphism in the surrounding rocks indicates that these have
crystallised at a low temperature
(CM 19.381-387).
At Bisbee, Cochise County, Arizona, USA, gormanite occurs in fractures in
tonalite with chlorite,
calcite and quartz
(HOM).
At the Chickering Mine, Walpole, Cheshire county, New Hampshire, USA, gormanite is rare in the
pegmatite deposit. Two known occurrences
of several specimens each have been collected. One comprises blue-green, partially embedded, fibrous masses in
siderite, the other medium to dark green lamellar sheaves over an aqua core.
These sheaves occur in very small primary phosphate dissolution
cavities in a medium grained siderite matrix.
Siderite and embedded childrenite
are the only associated minerals noted
(R&M 90.5.417).
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