chlorapatite

Chlorapatite is a mineral in the apatite group with the chemical formula Ca5(PO4)3Cl. It represents the chloride analogue of hydroxyapatite and fluorapatite, forming a solid-solution series Ca5(PO4)3X where X can be OH, F, or Cl. In chlorapatite, chlorine ions occupy the channels where hydroxyl groups are found in other apatite members.

The mineral typically crystallizes in the hexagonal system and forms as prismatic, often tabular crystals or in massive, granular aggregates. It has a vitreous luster, a Mohs hardness about 5, and a white to colorless appearance that may show pale tints of green, brown, or yellow due to impurities. Chlorapatite is relatively common in phosphate-bearing rocks and is frequently associated with fluorapatite and hydroxylapatite.

Chlorapatite occurs in a variety of geological settings. It can form in igneous and metamorphic rocks, especially where chlorine activity is high, such as in certain carbonatites and pegmatites. It can also appear in sedimentary phosphate deposits as part of the broader apatite group. The formation and stability of chlorapatite are influenced by the chemical environment, particularly the availability of chloride and the absence or presence of hydroxyl in the framework.

Economically, chlorapatite is a source of phosphorus when phosphate rocks are mined for fertilizer production. The mineral contributes to the phosphate content of ore, and its presence, along with other apatite members, affects processing and refining in phosphate industries.