Mineral
Apatito
Ca₅(PO₄)₃(F,Cl,OH) · Fosfatos
Apatite is a calcium phosphate with formula Ca5(PO4)3(F, Cl, OH) that crystallises in the hexagonal system and gives its name to the apatite group.
Its three principal varieties—fluorapatite, chlorapatite and hydroxylapatite—share the same hexagonal architecture. This framework is the structural prototype for a broad family of minerals with analogous compositions. Pyromorphite, mimetite and vanadinite are lead apatites that replace calcium by lead and phosphorus by arsenic or vanadium without changing the lattice type.
It occurs in diverse geological settings and is often recognised in green or violet colours. In the volcanic environment of Lebrija, brown–orange apatite has been described. There it may occur with prehnite and actinolite.
Durango apatite is used as a calibration standard in laboratories worldwide. Relatively large, homogeneous crystals that contain small amounts of uranium and thorium enable its use as a reference material for fission-track and U–Th/He dating. Its age is fixed at about 31.4 million years and is used to verify instruments and measurement protocols. Vials with yellow fragments are common in geochronology laboratories in the United States, Australia, Japan or Switzerland.
Etymology
Apatite: Pandora's box The name carries mythological weight. Apatite appears in colours and forms that imitate precious gems (beryl, peridot, tourmaline). It misled collectors and experts for centuries. Its name comes from the Greek apate (ἀπάτη), meaning "deceit". But Apate was not just any word: in Greek mythology, Apate was the goddess of deceit, one of the malevolent spirits that emerged from Pandora's box. To name a mineral thus is to accuse it of being one of the plagues of humanity.