Listing description
Biotite is a name used for a large group of black mica minerals that are
commonly found in igneous and metamorphic
rocks. These include: annite, phlogopite,
siderophyllite, fluorophlogopite, fluorannite, eastonite and many others. These
micas vary in chemical composition but are all sheet silicate minerals with very similar physical properties.
Detailed description
A generalized chemical composition for the
biotite group is:
K(Mg,Fe)2-3Al1-2Si2-3O10(OH,F)2
The name "biotite" is used in the
field and in entry-level geology courses because these minerals generally can not be distinguished without
optical, chemical or x-ray analysis.
Biotite is a primary mineral found in a wide
range of crystalline igneous rocks such as granite, diorite, gabbro, peridotite and pegmatite. It also
forms under metamorphic conditions when argillaceous rocks are exposed to heat
and pressure to form schist and gneiss. Although
biotite is not very resistant to weathering and transforms into clay minerals,
it is sometimes found in sediments and sandstones.
Properties of Biotite
Biotite is very easy to identify and with a
little experience a person will be able to recognize it on sight. It is a black
mica with perfect cleavage and a vitreous luster on the cleavage faces. When
biotite is separated into thin sheets, the sheets are flexible but will break
upon severe bending. When held up to the light the sheets are transparent to
translucent with a brown, gray or greenish color. Experienced observers can
sometimes recognize phlogopite by its brown color.
Physical
Properties of Biotite
|
Chemical Classification
|
dark mica
|
Color
|
black, dark green, dark brown
|
Streak
|
white to gray, flakes often produced
|
Luster
|
vitreous
|
Diaphaneity
|
thin sheets are transparent to translucent, books are opaque
|
Cleavage
|
basal, perfect
|
Mohs Hardness
|
2.5 to 3
|
Specific Gravity
|
2.7 to 3.4
|
Diagnostic Properties
|
dark color, perfect cleavage
|
Chemical Composition
|
K(Mg,Fe)2-3Al1-2Si2-3O10(OH,F)2
|
Crystal System
|
monoclinic
|
Uses
|
very little industrial use
|
Biotite Minerals
As noted above, biotite is a name used for a
number of black mica minerals that have different chemical compositions but
very similar physical properties. These minerals generally can not be
distinguished from one another without laboratory analysis. A small list of the
biotite minerals is given below with their chemical compositions.
Mineral
|
Chemical Composition
|
Annite
|
KFe3(AlSi3)O10(OH)2
|
Phlogopite
|
KMg3(AlSi3)O10(OH)2
|
Siderophyllite
|
KFe2Al(Al2Si2)O10(F,OH)2
|
Eastonite
|
KMg2Al(Al2Si3)O10(OH)2
|
Fluorannite
|
KFe3(AlSi3)O10F2
|
Fluorophlogopite
|
KMg3(AlSi3)O10F2
|
Uses of Biotite
Biotite has a small number of commercial uses.
Ground mica is used as a filler and extender in paints, as an additive to
drilling muds, as an inert filler and mold-release agent in rubber products,
and as a non-stick surface coating on asphalt shingles and rolled roofing. It
is also used in the potassium-argon and argon-argon methods of dating igneous
rocks.
PRICE
$10/KG OR $4.54/IB
For more information:
mobile: +2348039721941
contact person: emeaba uche
e-mail: emeabau@yahoo.com