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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
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 -
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Santabarbaraite from Wannon Falls -
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