Phosphosiderite

Phosphosiderite is a member of the metavariscite group,[2] and probably forms a complete series with metavariscite. It is the dimorph of strengite.[3] It is totally soluble in Hydrochloric acid and nearly insoluble in nitric acid.[4] It is usually cut into a cabochon shape for jewelry, and used as an ornamental stone.[3] It mainly consists of oxygen (51.38%), iron (29.89%) and phosphorus (16.58%), but contains hydrogen (2.16%) as well.[5]

Phosphosiderite is often found in a bright orchid-purple tint with yellow-colored streaks. The vein-like streaks found in the stone are known as cacoxenite. Four other rare color variants are rose red, brown-reddish yellow, mossy green, and dark shades of purple. Phosphosiderite can also be found as a colorless mineral.[6] It is pleochroic; on the X axis around 4° it is light rose, on the Y axis it is carmine red, and on Z it is colorless.[6]

Phosphosiderite is mined in some parts of Chile, Argentina, Germany, Portugal, and the United States. It occurs in association with strengite, turquoise, triphylite, leucophosphite, huréaulite, barbosalite and laueite.[7] In zoned granitic pegmatites, it usually occurs as an alteration product of primary phosphates. This makes it a secondary phosphate.[3] It may be replacing shells and bones, and can occur in the soil as a component of it as well.[7] However, the latter is rarer.[3]