Fluorapatite

Fluorapatite is a calcium phosphate mineral (Ca₅(PO₄)₃F), the fluorine-rich and most abundant member of the apatite group and the reference mineral for hardness 5 on the Mohs scale. Apatite is the most common phosphate mineral on Earth and the defining mineral of hardness 5 on the Mohs scale. Fluorapatite (the fluorine-dominant variety) is the most abundant apatite species, forming in igneous, metamorphic, and sedimentary environments.

What makes apatite remarkable is its biological role: your bones and teeth are made of hydroxyapatite, a close relative of fluorapatite. When fluoride is added to drinking water or toothpaste, it converts tooth hydroxyapatite to the more acid-resistant fluorapatite - this is literally the chemistry of cavity prevention. Fluorapatite in your teeth is the same mineral species as the neon blue gemstone.

Gem-quality apatite comes in a spectacular range of colors: neon blue-green from Paraiba-type localities (colored by manganese and rare earth elements), vivid purple (manganese), bright yellow (iron), and pink (manganese and rare earths). The neon blue-green variety from Madagascar and Brazil has surged in popularity as an affordable alternative to Paraiba tourmaline.

Apatite is identified by its hexagonal crystal habit, hardness of exactly 5 (the Mohs scale reference mineral), and characteristic colors. The neon blue-green variety is particularly distinctive.

Distinguish from tourmaline (harder at 7, different crystal shape), beryl (harder at 7.5-8), and fluorite (softer at 4, cubic not hexagonal). Apatite's hardness of 5 is its most practical diagnostic - it's scratched by a knife (5.5) but not by a copper coin (3.5). This makes it too soft for most ring settings but fine for pendants and earrings.