Phosphosiderite

Phosphosiderite typically forms as an alteration product of triphylite in zoned complex granite pegmatites; it may also occur in soils and replacing bones or shells. Its type locality is the Kalterborn mine near Eiserfeld, Siegen, Germany, and it is known in small amounts from many localities, including Germany, France, Portugal, Sweden, Mozambique, the USA, Canada, Brazil (Sapucaia and nearby pegmatites, Minas Gerais) and Argentina. Gemmological records cite massive cabochon material from the Copiapó area, Atacama, Chile.

Phosphosiderite is soft (3.5 to 4) and has a high refractive index for a purple opaque stone, with spot readings of about 1.69–1.71 recorded on cabochons. Gem laboratory reports compiled by Gemsdat describe purple phosphosiderite cabochons that were filled with epoxy resin and sold as "purple jade", and others impregnated with a polymer; the "purple jade" name is misleading. Its strong pleochroism (pale rose-red, carmine-red, colourless) can be seen only in transparent crystals.

Phosphosiderite was first found by Alfred Des Cloizeaux in 1858, who called it "type I hureaulite". Willy Bruhns and Karl Busz named it in 1890 from its composition: phosphate and the Greek "sideros" for iron.