What is Vauxite?
Vauxite is a delicate hydrated iron-aluminium phosphate, famous for blue to blue-green crystals from phosphate-rich granite pegmatites.
Mineralogy and structure
Reference formula: FeAl2(PO4)2(OH)2·6H2O. Vauxite is triclinic, strongly hydrated and commonly associated with metavauxite and other phosphate minerals. The exact COD 9000171 model is used; hydration makes crystals fragile. Vauxite is classified with phosphates and has triclinic crystal symmetry. Typical hardness is 2.5–3 on the Mohs scale and specific gravity is approximately 2.5–2.7.
Colour, lustre and habit
Typical colours include blue, blue-green, green, colourless, white. The usual prismatic, tabular, radiating habit and vitreous, pearly lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Vauxite forms in or is associated with granite pegmatites, phosphate-rich cavities and secondary alteration of iron-bearing phosphates. Important documented localities include Huanuni in Bolivia, Brazil, Portugal, Germany and the United States.
Blue phosphate crystals from a pegmatite
Vauxite is a collector favourite because a soft, hydrated phosphate can show unusually clear blue colour and elegant crystal form. Freshness and matrix context determine whether a specimen survives as a reference piece.
Collecting and care
Keep dry and protected from vibration, heat, acids and abrasion. Do not soak; support fine sprays and retain the pegmatite locality.
