Fluorapatite

Class: Phosphates, arsenates, vanadates
Group: Apatite

The most common rock-forming phosphate mineral; accessory in most igneous rocks, important in syenites, alkaline rocks, carbonatites, granite pegmatites; common in marbles and skarns (Anthony et al., 2001—2005).

Fluorapatite — specimen 0057, photo © NMNHS

Original description: ‘Apatit’ Rammelsberg, C. F., 1860. Apatit — Handbuch der Mineralchemie, Wilhelm Engelmann, Leipzig: 351—355 [view in ‘Library’].

Type locality: Greifenstein, Ehrenfriedersdorf, Erzgebirge, Saxony, Germany.

Type material: unknown.

Etymology: renamed from the original ‘apatite’ to emphasise the chemical composition. Apatite is from the Greek απατείν (apatein), ‘to deceive’, as it was often confused with other minerals.

Distribution: many localities: Afghanistan: Kunar Province; Brazil: Minas Gerais, Nova Lima; Canada: large crystals from southeastern Ontario; Germany: Saxony, at Ehrenfriedersdorf; Mexico: Durango, Cerro de Mercado; Pakistan: Gilgit-Baltistan; Russia; South Africa (Anthony et al., 2001—2005). Facetable material is known from Madagascar.

Chemistry

Ca5(PO4)3F

Essential elements: oxygen (O), fluorine (F), phosphorus (P), calcium (Ca).

Crystal data

Crystallography: hexagonal — dipyramidal. Crystal habit: as prismatic hexagonal crystals, elongated on [0001], to 2 m; as complex tabular to discoidal crystals flattened on {0001}, typically with many forms; granular, globular to reniform, nodular, massive. Twinning: rare as contact twins on {1121} or {1013} (Anthony et al., 2001—2005).

Physical properties

Cleavage: poor on {0001} and {1010} (Anthony et al., 2001—2005). Fracture: uneven to conchoidal (Anthony et al., 2001—2005). Tenacity: brittle (Anthony et al., 2001—2005). Hardness: 5 (Anthony et al., 2001—2005). Density: 3.1—3.25 g/cm3 (Anthony et al., 2001—2005). Luminescence: may be cathodoluminescent, phosphorescent, or fluorescent in UV (Anthony et al., 2001—2005).

Optical properties

Colour: sea-green, violet, purple, blue, pink, yellow, brown, white, colourless; may be zoned; colourless or faintly tinted in thin section (Anthony et al., 2001—2005). Diaphaneity: transparent to translucent (Anthony et al., 2001—2005). Lustre: vitreous to subresinous (Anthony et al., 2001—2005). Refractive index: 1.631—1.646 — anisotropic [uniaxial (-)] (Anthony et al., 2001—2005). Dispersion: no data. Pleochroism: weak to strong if coloured (Anthony et al., 2001—2005).

Material from ‘Repository’

2 specimens: 0057 — 0.82 ct, Madagascar; 0013 — 0.45 ct, Madagascar.

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