Apatite

Lore & Background

The name derives from the Greek word ἀπατάω (apatáō), meaning 'to deceive', reflecting its frequent misidentification for other minerals. Apatite is very common as an accessory mineral in igneous and metamorphic rocks, usually as small grains visible only in thin section, though coarsely crystalline forms occur in pegmatites, gneiss, skarns, and marble. It is also found in clastic sedimentary rocks and in phosphorite, a phosphate-rich sedimentary rock containing up to 80% apatite as cryptocrystalline masses called collophane.

Reader's Guide

Apatite holds broad significance across geology, biology, and industry. As the defining mineral for hardness 5 on the Mohs scale, it aids in field identification of rocks. Hydroxyapatite is a major component of tooth enamel and bone mineral, while fluorapatite's resistance to acid attack led to the discovery that fluoridated water reduces dental caries, a finding applied in water fluoridation and toothpaste. Apatite is the primary source of phosphate for fertilizer and other industrial uses, and it has been used as a gemstone, as a pigment for the Terracotta Army, and in Qing dynasty enamel. Fission tracks and (U-Th)/He dating of apatite are established methods for determining thermal histories of orogenic belts and sedimentary basins. Apatite also serves as an ore for rare-earth elements, though it often contains uranium and its decay-chain nuclides. The mineral group is also studied for potential nuclear waste storage and for immobilizing toxic heavy metals.

Did You Know?

• Apatite is named from the Greek word ἀπατάω (apatáō), meaning 'to deceive', because it is often mistaken for other minerals.
• Fluorapatite is more resistant to acid attack than hydroxyapatite, leading to the use of fluoridated water to reduce dental caries.
• Apatite is the defining mineral for hardness 5 on the Mohs scale.