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Apatite Ca5(PO4)3(OH,F,Cl)
Crystal system: Hexagonal
Refractive index: 1.624-1.667
Birefringence: 0.001-0.007
Cleavage: poor
Twinning: rare
Colour in PPL: generally colourless
Pleochroism: may show weak
Relief: low to moderate
Distinction: high relief and low birefringence
Occurrence: occurs in igneous rocks, but in pottery often occurs as sedimentary deposit perhaps associated with bone
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Phosphate Ooid - Plain polarised light
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