Apatite

Apatite forms in igneous, metamorphic and sedimentary rocks. The largest deposits are marine phosphate rocks (phosphorite), mined for fertilizer; gem crystals grow in pegmatite pockets and hydrothermal veins. Brazil, Canada, India, Madagascar and Mexico produce most gem apatite: blue from Brazil, Myanmar and Sri Lanka; neon blue-green from Madagascar; yellow from Durango, Mexico, and Murcia, Spain; violet from Maine and Germany; and cat's-eye stones from Brazil, India, Myanmar, Sri Lanka and Tanzania.

Apatite can be scratched by a steel knife, is brittle, and shows a refractive index around 1.63 to 1.65 with low birefringence; blue and yellow stones often show a rare-earth (didymium) absorption spectrum. Faceted apatite can be hard to separate from tourmaline because many properties overlap, but tourmaline is harder. Neon blue-green apatite resembles Paraíba tourmaline. Synthetic apatite made for laser research has entered the gem trade and may show a color change, which natural apatite does not. "Asparagus stone" is a trade name for light green apatite. Heat treatment is common.

Apatite is brittle and sensitive to acids, heat and shock. Rings need protective settings and only occasional wear; earrings, pendants and pins are safer. Store and clean it as gently as opal: never use mechanical (ultrasonic or steam) cleaning systems.

The name comes from the Greek apatein, "to deceive", because early mineralogists confused apatite with other species. Before the discovery of neon blue-green apatite in Madagascar, the gem was rarely used in jewelry and was valued mainly by collectors for its colors and fluorescence.