Chemical composition: Ca5 (P04)3(0H, F, Cl), Flour apatite is most common. Mn and Sr may replace Ca to some extent.
(i) Form: Prismatic crystals, colloform, massive, mammillated, concretionary and granular.
(ii) Colour: Usually in shades of green or brown; also blue, violet and colourless.
(iii) Lustre: Subresinous to vitreous.
(iv) Streak: White.
(v) Hardness: 5.
(vi) Cleavage: One set poorly developed.
(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.