Images
Formula: Fe3+Al2(PO4)2(OH)3.7H2O
Hydrated phosphate containing hydroxyl, laueite group
Crystal System: Triclinic
Specific gravity: 2.35 measured, 2.40 calculated
Hardness: 3
Streak: White
Colour: Light brown, straw-yellow
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).
Ferrivauxite is an oxidised equivalent of
vauxite and forms oxidation
pseudomorphs after that mineral. It occurs in association with
sigloite and crandallite at Llallagua
(MM 80.2.311–324).
Back to Minerals