Metavauxite

metavauxite

vauxite

paravauxite

wavellite

Images

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

Hydrothermal 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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