Material name Biotite
Composition KMg2Fe(AlSi3O10)(OH)2
Chemical formula weight 448.80
System Monoclinic
Temperature (ºC) r.t.
a (Å), b (Å), c (Å) 5.345(1) 9.258(2) 10.222(2) @
α (deg), β (deg), γ (deg) 90 100.23(2) 90 @
Unit cell volume (Å3) 497.8
Calculated density (g/p3) 2.99
Z 2
Space group C2/m (No.12)
atom site g x/a y/b z/c B2)
K 2b 1 0 1/2 0 2.95(5)
Mg 4h 1 0 0.3347(1) 1/2 1.00(2)
Fe 2c 1 0 0 1/2 0.93(3)
Si 8j 0.75 0.0748(1) 0.1669(1) 0.2257(1) 0.76(2)
Al 8j 0.25 0.0748(1) 0.1669(1) 0.2257(1) 0.76(2)
O1 4i 1 0.0267(6) 0 0.1687(3) 1.71(8)
O2 8j 1 0.3195(4) 0.2361(3) 0.1681(2) 1.66(5)
O3 8j 1 0.1316(3) 0.1677(2) 0.3909(2) 1.03(4)
O4 8j 0.5 0.1291(5) 1/2 0.3947(3) 1.16(8)
H 8j 0.5 0.09 1/2 0.315  -

Reference: M.F. Brigatti and P. Davoli, American Mineralogist, 75, 305 (1990).