Zwieselite

General Information:
 Chemical Formula:
(Fe++,Mn)2(PO4)F
 Composition:
(Molecular Weight = 225.21 gm)
Manganese 12.20 % Mn
Iron 37.20 % Fe
Phosphorus 13.75 % P 
Oxygen 28.42 % O 
Fluorine 8.44 % F 
 Empirical Formula:
Fe2+1.5Mn2+0.5(PO4)F
Physical Properties:
 Cleavage:
[001] Good, [010] Distinct, [100] Indistinct
 Color:
dark brown, black, or black brown.
 Density:
3.927 - 3.97, Average = 3.94
 Diaphaniety:
Translucent
 Hardness:
5-5.5 - Apatite-Knife Blade
 Luster:
Vitreous - Resinous
 Streak:
white
More details...