Apatite is a group of blue-green phosphate minerals, chemically calcium phosphates with variable fluorine, chlorine, or hydroxyl content. Known for its vivid color range and hexagonal crystals, apatite is both a collector’s gemstone and a key industrial source of phosphorus used in fertilizers.
Key facts
- Chemical formula: Ca₅(PO₄)₃(F, Cl, OH)
- Crystal system: Hexagonal
- Hardness: 5 on the Mohs scale
- Luster: Vitreous to glassy
- Common colors: Neon blue-green, yellow, violet, colorless
Composition and varieties
Apatite comprises closely related minerals—fluorapatite, chlorapatite, and hydroxylapatite—that differ only by the dominant anion in their structure. Fluorapatite is the most abundant and is often gem-quality, while hydroxylapatite forms the inorganic component of bones and teeth. Substitutions of carbonate or manganese create varieties such as carbonate-apatite and manganapatite.
Physical characteristics
The mineral typically forms transparent to translucent prismatic crystals, though massive and granular habits also occur. Its glassy luster and strong pleochroism (especially in blue-green stones) give it striking visual appeal, but a hardness of only 5 makes it brittle and sensitive to scratches, limiting everyday jewelry use. Under ultraviolet light, apatite may fluoresce in hues from violet-blue to greenish-yellow depending on composition.
Gemstone significance
Collectors prize neon blue-green apatite—particularly fluorapatite from Madagascar and Brazil—for its tropical “paraíba-like” hue. Yellow apatites from Mexico and green stones from Canada are also valued. The gem’s brilliance rivals tourmaline or beryl, yet its softness demands protective settings and occasional wear. Heating can enhance blue and blue-green tones, while cat’s-eye varieties exhibit chatoyancy.
Geological and practical importance
Apatite is widespread in igneous, metamorphic, and sedimentary rocks, often occurring as accessory crystals. It is the chief natural source of phosphorus, vital for agricultural fertilizers and chemical production. In biology, synthetic and natural hydroxylapatite are used for bone grafts, dental implants, and tissue engineering, reflecting the mineral’s role in both Earth’s crust and living organisms.