Biotite

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Biotite
Biotite aggregate - Ochtendung, Eifel, Germany.jpg
Thin tabular biotite aggregate
(Image width: 2.5 mm)
General
CategoryDark mica series
Formula
(repeatin unit)
K(Mg,Fe)
3
(AlSi
3
O
10
)(F,OH)
2
Creestal seestemMonoclinic (2/m)
Space Group: C 2/m
Identification
Formula mass433.53 g
ColourMirk broun, greenish-broun, blackish-broun, yellae, white
Creestal habitMassive tae platy
TwinninCommon on the [310],
less common on the {001}
CleavagePerfect on the {001}
FracturMicaceous
TenacityBrickle tae souple, elastic
Mohs scale haurdness2.5–3.0
SkinkleVitreous tae pearly
StreakWhite
DiaphaneitySkyre tae leamin tae opaque
Speceefic gravity2.7–3.1
Density2.8–3.4
Optical propertiesBiaxial (-)
Refractive indexnα = 1.565–1.625
nβ = 1.605–1.675
nγ = 1.605–1.675
Birefringenceδ = 0.03–0.07
PleochroismStrong
Dispersionr < v (Fe rich);
r > v weak (Mg rich)
Ultraviolet fluorescenceNone
References[1][2][3]

Biotite is a common phyllosilicate meeneral athin the mica group, wi the approximate chemical formula K(Mg,Fe)
3
AlSi
3
O
10
(F,OH)
2
. Mair generally, it refers tae the dark mica series, primarily a solid-solution series atween the iron-endmember annite, an the magnesium-endmember phlogopite; mair aluminous endmembers include siderophyllite. Biotite wis named bi J.F.L. Hausmann in 1847 in honour o the French pheesicist Jean-Baptiste Biot, who, in 1816, researched the optical properties o mica, discovering mony unique properties.[4]

Biotite is a sheet silicate. Airn, magnesium, aluminium, silicon, oxygen, an hydrogen furm sheets that are waikly boond thegither bi potassium ions. It is whiles cried "iron mica" acause it is mair airn-rich nor phlogopite. It is an aa whiles cried "black mica" as opponed tae "white mica" (muscovite) – baith furm in some rocks, in some instances side-bi-side.

References[eedit | eedit soorce]

  1. Biotite mineral information and data Mindat
  2. Biotite Mineral Data Webmineral
  3. Handbook of Mineralogy
  4. Johann Friedrich Ludwig Hausmann (1828). Handbuch der Mineralogie. Vandenhoeck und Ruprecht. p. 674. "Zur Bezeichnung des sogenannten einachsigen Glimmers ist hier der Name Biotit gewählt worden, um daran zu erinnern, daß Biot es war, der zuerst auf die optische Verschiedenheit der Glimmerarten aufmerksam machte." (For the designation of so-called uniaxial mica, the name "biotite" has been chosen in order to recall that it was Biot who first called attention to the optical differences between types of mica.)