This relatively rare gemstone is a form of iron phosphate. This chemical compound is also used to fortify many foods including bread.
Phosphosiderite used for decorative purposes comes mainly from Chile. The mineral is massive which means crystals occur as one large tightly intergrown mass. Although individual crystals do occur, they're very rare.
Despite its unique colour, phosphosiderite is rarely used as a gemstone because it's soft and brittle. This make cutting and polishing difficult.