Apatite

Physical Properties
Chemical formula Ca5(PO4)3(OH,F,Cl)
Class Phosphate
Crystal system Hexagonal
Habit Typically prismatic
Colloform
Massive
Granular
Color Green
Yellow
Variable
Hardness 5
Specific gravity 3.2
Cleavage Good (001), poor {100}
Fracture Conchoidal
Luster Subresinous
Transparency Transparent to translucent
Streak White
Optical Properties
PPL Colorless
Nonpleochroic
XPL 1st order grey
Often plucked; you may see a
small prismatic hole indicative
of apatite
δ 0.003
after Perkins, 400

Apatite in Hand Sample

Three subhedral apatite crystals

Apatite (green) in orthoclase

Greenish apatite in slabbed nelsonite

Greenish apatite in uncut nelsonite

Apatite in Thin Section

Apatite is obnoxious in thin section. More often than not, it plucks out in grinding, leaving a little hexagonal “apatite wuz here” hole in your section. That’s why there’s nothing here yet. We’re working on it.

Further Reading

Apatite at webmineral.com

Apatite at mindat.org