Apatite is a group name, applied to phosphates, arsenates and vanadates. It's members are
the most common of the phosphorus-bearing minerals. The group members are differentiated on
the basis of their predominant anions i.e. fluorapatite (FL), hydroxylapatite (OH), or
chloroapatite (CL). Apatites are formed under a variety of conditions but most commonly
occur as accessory minerals in igneous rocks. They also occur in marine sedimentary rocks
formed by chemical deposition, in fossils, and in metamorphic rocks.
Apatites vary widely in color from colorless to yellow, green, brown, red and blue. Some
apatites display a yellow fluorescence under ultraviolet light. Group members exhibit hexagonal,
prismatic crystals which may be stubby to elongated and are often terminated by dipyramidal
faces.
Rocks from Martin Friedlander's Collection