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Formula: Fe2+Al2(PO4)2(OH)2.8H2O
Hydrated phosphate containing hydroxyl, monoclinic paramorph of triclinic
paravauxite
(The name "metavauxite" would usually indicate that the mineral was a dehydration product of "vauxite", but actually it
is more hydrated, not less. This may be because metavauxite was initially assumed, incorrectly, to be a lower hydrate).
Crystal System: Monoclinic
Specific gravity: 2.345 measured, 2.36 calculated
Hardness: 3
Streak: White
Colour: Colourless, white, light green, colourless in transmitted light
Environments
Metavauxite is a rare supergene secondary mineral in the
oxidised zone of tin mines, associated with
vauxite, paravauxite,
wavellite and quartz
(HOM).
Localities
At the type locality, the Siglo Veinte Mine, Llallagua, Rafael Bustillo, Potosí, Bolivia, metavauxite occurs in the
oxidised zone of tin veins, associated with
wavellite, vauxite,
quartz and paravauxite
(Mindat, Dana).
Metavauxite always occurs on wavellite, which encrusts
brecciated fragments of porphyry
along faults cutting the veins. It is commonly found intimately associated with
paravauxite crystals which in some cases are perched on needles of
metavauxite, with an occasional rosette of blue vauxite crystals. Pale green
crystals of metavauxite have been found associated with paravauxite and
allophane, exceptionally to 5 cm in length. It has also been found in open
fissures that were coated with thin films of wavellite, on which were deposited
first paravauxite and then metavauxite
(Minrec 37.2.143-144).
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