Santabarbaraite

santabarbaraite

vivianite

metavivianite

ferrisymplesite

Images

Formula: Fe3+3(PO4)2(OH)3.5H2O
Hydrated phosphate
Crystal system: Amorphous
Specific gravity: 2.42 measured
Streak: Yellow to yellowish brown
Colour: Orange, orange-brown, yellowish brown
Luminescence: Not fluorescent under UV
Environments

Sedimentary environments

Santabarbaraite is amorphous to X-rays. It occurs in cavities within concretionary nodules, in clays in a clastic rock sequence (Italy) and in clay underlying basalt (Australia) (HOM).

Localities

The type locality is the Santa Barbara lignite district, Upper Valdarno, Tuscany, Italy. Santabarbaraite, a new (in 2000) amorphous phosphate mineral, has been found here and also at Wannon Falls, Wannon River, Wannon, Southern Grampians Shire, Victoria, Australia. The mineral is the result of in situ oxidation of vivianite, occurring as pseudomorphs after vivianite crystals that are up to 3 mm across in concretionary nodules at the type locality and somewhat larger at Wannon Falls. Santabarbaraite is brown to light-brown in hand specimen, but appears yellowish amber under the microscope and has a similar streak. It is translucent with a distinct vitreous to greasy lustre and is nonfluorescent.
Santabarbaraite from both localities was analysed, and the reults show that all the Fe in santabarbaraite is trivalent Fe3+, associated with the presence of both H2O and hydroxyl. This is consistent with an oxidation series from vivianite through metavivianite to santabarbaraite, involving progressive oxidation of Fe2+ accompanied by conversion of H2O ligands to OH- ions. Such a process leads to a gradual collapse of the vivianite structure as hydrogen bonds are eliminated. Santabarbaraite is the end product of this process and can be thus considered the phosphorus analogue of ferrisymplesite (EJM 15.185-192).
Santabarbaraite from theSanta Barbara Mine - Image
Santabarbaraite from Wannon Falls - Image

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