Chemical composition: Ca5 (P04)3(0H, F, Cl), Flour apatite is most common. Mn and Sr may replace Ca to some extent.

Physical properties:

(i) Form: Prismatic crystals, colloform, massive, mammillated, concretionary and granular.

(ii) Colour: Usually in shades of green or brown; also blue, violet and colourless.

ADVERTISEMENTS:

(iii) Lustre: Subresinous to vitreous.

(iv) Streak: White.

(v) Hardness: 5.

(vi) Cleavage: One set poorly developed.

ADVERTISEMENTS:

(vii) Fracture: Conchoidal to uneven.

(viii) Specific gravity: 3.15 – 3.2.

(ix) Diaphaneity: Transparent to translucent.

Use: Serves as a source of phosphate for fertilizer and production of phosphorus chemicals. Transparent varieties are used as gemstones.