triphylitemontebrasite

Triphylite-montebrasite is a mineral series belonging to the triphylite group, which are phosphates of lithium and alkali or alkaline earth metals. The series represents a solid solution between two end-members: triphylite, with the ideal formula LiFePO4, and montebrasite, with the ideal formula LiAlPO4(OH,F). The mineral is often found in pegmatites and is characterized by its variable composition, with iron and aluminum substituting for each other, along with hydroxyl and fluoride ions.

The color of triphylite-montebrasite can range from grayish-white or pale yellow in montebrasite to bluish-gray, greenish, or even black in triphylite. It typically occurs in massive or granular forms, though prismatic crystals are also known. Hardness is generally between 4.5 and 5 on the Mohs scale, and it possesses a vitreous to greasy luster. Triphylite-montebrasite is an important source of lithium and manganese, and its formation is often associated with the late stages of granitic pegmatite crystallization. The geological occurrence of this mineral series is global, with notable deposits found in Brazil, the United States, and Madagascar. Its chemical variability makes it a subject of interest for mineralogists studying solid solution series in silicate and phosphate minerals.