K(Fe2+,Mg)3(AlSi3O10)(OH,F)2
Biotite, one of the several members of the mica group found at MSH is fairly abundant in many environments and as a rock-forming mineral. It is difficult to distinguish from annite.
PHYSICAL CHARACTERISTICS:
Color is usually dark red brown to black.
Luster is vitreous to submetallic.
Diaphaneity is transparent to opaque.
Crystal System is monoclinic; C2/m.
Crystal Habits include short to long pseudohexagonal prisms
to several centimeters across.
Cleavage {001} is perfect.
Fracture is not apparent due to cleavage.
Hardness is 2.5 – 3.
Specific Gravity is approximately 2.8 g/cm3.
Streak is white.
Associated Minerals include aegirine, analcime, gmelinite,
gonnardite, microcline, monteregianite, natrolite and zircon.
Distinguishing Features: Crystal habit.
Origin: Named in 1847 after Jean Baptiste Biot (1774-1862),
French physicist and chemist who first called attention to the
optical difference in micas.
CLASSIFICATION:
Dana System
# 71.2.2b.2
Strunz Classification
# VIII/H.11-40
REFERENCES:
MinRec 21:299 (1990), Dana 8:1458-1460 (1997)
DISTRIBUTION AND RARITY AT MONT SAINT-HILAIRE:
MSH PE AP MX SS MC HF BR SX FR
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