Sigloite

sigloite

wavellite

paravauxite

childrenite

Images

Formula: Fe3+Al2(PO4)2(OH)3.7H2O
Hydrated phosphate containing hydroxyl, laueite group
Specific gravity: 2.35
Hardness: 3
Streak: White
Colour: Light brown, straw-yellow
Environments

Hydrothermal environments

Localities

The type locality, the Siglo Veinte Mine, Llallagua, Rafael Bustillo, Potosí, Bolivia, is a hydrothermal tin deposit. Here cavities were found filled with straw yellow intergrowths of crystals of sigloite; in other cavities similar crystals were perched on wavellite overgrowths on quartz. Most of the ferrous iron (Fe2+) of paravauxite had been oxidised to the ferric state (Fe3+), forming sigloite as an oxidation pseudomorph after paravauxite, apparently as a supergene stage later than the hydrothermal alteration which formed the minerals associated with sigloite; these minerals include wavellite, paravauxite, metavauxite, crandallite, childrenite, vauxite and quartz, and are found in open fractures cutting major cassiterite veins (AM 47.1-8, HOM).

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