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Apatite Mineral Facts:

Chemical Formula: Ca₅(PO₄)₃(OH,F,Cl)
Phosphate and fluoride of calcium, or phosphate and chloride of calcium ; the first being fluorapatite, Ca₅(PO₄)₃(F), the second chlorapatite, Ca₅(PO₄)₃(Cl). Usually some amounts of both chloride and fluoride are present together.

Colors: Usually shades of green or brown, but also sometimes yellow, blue, violet and colorless.

Hardness: 5
Hardness is such that is can just be scratched with a steel knife blade.

Density: 3.15 to 3.20

Cleavage: One poor cleavage on 0001.  Fracture is conchoidal and uneven: brittle.

Crystallography: Hexagonal

Luster:. Vitreous, transparent to translucent - on rare occasions it is used as a gemstone.

Optics: (Refractive Index)  = 1.63
 

Composition, Structure and Associated Minerals:
Apatite is widely distributed in all classes of rocks - igneous, sedimentary and metamorphic. It occurs in some igneous rocks as small prismatic crystals, giving lath-shaped longitudinal sections and hexagonal cross-sections.  Apatite commonly forms as prismatic crystals, showing the hexagonal cross section and often terminated by bi-pyramidal faces. Where crystals are clean and clear, Apatite is sometimes used as a gemstone, however its lack of sufficient hardness keeps it from gaining real popularity in that regard - it is considered to be more of a collector gemstone. A deposit of brightly colored material from Africa was termed "neon" apatite.

There are two major divisions of natural calcium phosphates; they are (1) Apatite, which has a definite chemical composition; and (2) Rock phosphates, such as phosphorite, phosphatic limestone, guano, and bone beds, which are mixed with considerable amounts of impurities and have no definite chemical composition. While the phosphate minerals found in animal bones and teeth are forms of the mineral apatite, the make up of the organically derived calcium phosphate varies considerably.

Identification and Diagnostics
Apatite is distinguished by its crystals, color and hardness. It is sometimes confused with beryl as both are found in pegmatite rocks. Apatite is considerably softer than beryl as Apatite crystals can be scratched with a hard steel knife blade. Apatite can be melted with difficulty, and is soluble in some strong acids - once taken into solution it gives a positive test for the presence of phosphates.

Industrial Uses of Apatite
Large bedded deposits of impure apatite, or "phosphate rock" occur in various places across the world. This material is mined as the most important industrial source of phosphates. Phosphate chemicals are used in a wide variety of applications, but the largest use of phosphate is in the fertilizer industry for agriculture.

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