Turpinite
Turpinite is a rare, hydrated phosphate mineral with the chemical formula (Mn,Fe)5(PO4)2(OH)4•2H2O. It is a secondary mineral, typically formed through the alteration of primary manganese phosphates in phosphate-rich pegmatites or hydrothermal deposits.
It is characterized by its brownish-red to dark brown color, often occurring as earthy masses, fibrous aggregates, or microscopic crystals. Its luster is typically dull or silky. Turpinite is relatively soft, with a Mohs hardness of around 3.5. It is also relatively lightweight.
Turpinite is found in a limited number of locations worldwide, often associated with other secondary phosphate minerals such as strengite, phosphosiderite, and cacoxenite. Some notable occurrences include regions in France, Germany, and the United States.
Identification of turpinite often relies on X-ray diffraction analysis, as its physical properties can be similar to those of other hydrated iron and manganese phosphates.