What is Phosphosiderite?
Phosphosiderite is a lilac to purple hydrated iron phosphate, popular as a polished stone and attractive botryoidal collector mineral.
Mineralogy and crystal structure
Reference formula: Fe3+4(PO4)3(OH)5·2H2O. Phosphosiderite is a hydrated monoclinic phosphate and may grade toward strengite in composition. Its colour can vary with iron oxidation and minor substitutions. Phosphosiderite is classified with phosphates and has a monoclinic crystal system. Typical hardness is 3.5–4 on the Mohs scale and specific gravity is approximately 2.7–2.8.
Colour, lustre and habit
Typical colours include lavender, purple, pink, red-brown. The usual botryoidal, massive, crusty habit and vitreous, pearly, earthy lustre help describe a specimen, but colour alone is not diagnostic.
Formation and notable localities
Phosphosiderite forms in or is associated with oxidised phosphate deposits, granite pegmatites and secondary mineral zones. Important documented localities include Chile, Argentina, Germany, Portugal, the United States and France.
Lavender phosphate with a soft polish
Phosphosiderite brings a refined purple tone to the phosphate family. Its colour and botryoidal texture make it commercially approachable without losing mineralogical depth.
Collecting and care
Protect from scratches, heat and acids; clean gently and avoid prolonged soaking.
