Biotite Mineral Data

General Biotite Information

Chemical Formula:

K(Mg,Fe++)3[AlSi3O10(OH,F)2

Composition:

Molecular Weight = 433.53 gm

Potassium 9.02 % K 10.86 % K₂O

Magnesium 14.02 % Mg 23.24 % MgO

Aluminum 6.22 % Al 11.76 % Al₂O₃

Iron 6.44 % Fe 8.29 % FeO

Silicon 19.44 % Si 41.58 % SiO₂

Hydrogen 0.41 % H 3.64 % H₂O

Oxygen 43.36 % O

Fluorine 1.10 % F 1.10 % F

- % F -0.46 % -O=F₂

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

KMg_2.5Fe²⁺_0.5AlSi₃O₁₀(OH)_1.75F_0.25

Environment:

Granitic rocks. Forms a series with phlogopite. Has several polytypes (1M, 3T, 2M1). Biotite is now a group name for phlogopite, siderophyllite and eastonite.

IMA Status:

Not Approved IMA 1998 - Bitote is now the group name

Locality:

Common world wide. Link to MinDat.org Location Data.

Name Origin:

Named in 1847 after the French physicist, Jean Baptiste Biot (1774 - 1862), who studied the optical properties of the micas.

Name Pronunciation:

Biotite

Synonym:

Iron Mica

Lepidomelane (Fe)

Manganophyllite (Mn)

Micaceous Iron Ore

Oxybiotite

Biotite Image

Images:

Biotite

Comments: Brown book of pseudohexagonal biotite crystals in matrix.
Location: Sattleberg, Laacher See, Rhineland-Palatinate, Germany. Scale: Size Not Given.
© Lou Perloff / Photo Atlas of Minerals

Images:

Biotite

Comments: Sharp hexagonal plates of dark brown biotite to 2.5 cm. across, with white albite.
Location: Brazil. Scale: 6.9x5.5x3 cm.
© Richard Dale / Dale Minerals

Images:

Biotite Anthophyllite

Comments: Fibrous mass of anthophyllite as a shell around biotite.
Location: Hermanov, Severocesky, Czech Republic. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Images:

Biotite Wohlerite

Comments: Prismatic wohlerite crystals with lepidomelane (Fe-rich biotite).
Location: Langevannet, Tvedalen, Telemark, Norway. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Biotite Crystallography

Axial Ratios:

a:b:c =0.5771:1:1.1046

Cell Dimensions:

a = 5.343, b = 9.258, c = 10.227, Z = 2; beta = 100.26° V = 497.79 Den(Calc)= 2.89

Crystal System:

Monoclinic - PrismaticH-M Symbol (2/m) Space Group: C 2/m

$Help on X Ray Diffraction:$ X Ray Diffraction:

By Intensity(I/I_o): 3.37(1), 10.1(1), 2.66(0.8),

Forms:

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Forms: ( 1 1 2) ( 2 2 1) ( 0 1 0) ( 0 0 1)

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Crystal Structure:

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Hendricks S B , Jefferson M E , American Mineralogist , 24 (1939) p.729-771, Polymorphism of the micas with optical measurements

View Additional jPOWD Structure files for Biotite
[1] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [2] [20] [21] [22] [23] [24] [25] [26] [27] [28] [3] [4] [5] [6] [7] [8] [9]

Physical Properties of Biotite

Cleavage:

{001} Perfect

Color:

Dark brown, Greenish brown, Blackish brown, Yellow, White.

Density:

2.8 - 3.4, Average = 3.09

Diaphaneity:

Transparent to translucent to opaque

Fracture:

Uneven - Flat surfaces (not cleavage) fractured in an uneven pattern.

Habit:

Lamellar - Thin laminae producing a lamellar structure.

Habit:

Micaceous - Platy texture with "flexible" plates.

Habit:

Pseudo Hexagonal - Crystals show a hexagonal outline.

Hardness:

2.5-3 - Finger Nail-Calcite

Luminescence:

Non-fluorescent.

Luster:

Vitreous - Pearly

Streak:

gray

Optical Properties of Biotite

Gladstone-Dale:

CI meas= 0.026 (Excellent) - where the CI = (1-KPDmeas/KC)
CI calc= -0.044 (Good) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2163,KPDmeas= 0.2016,KC= 0.2071
Ncalc = 1.58 - 1.7

Optical Data:

Biaxial (-), a=1.565-1.625, b=1.605-1.675, g=1.605-1.675, bire=0.0400-0.0500, 2V(Calc)=0, 2V(Meas)=0-25. Dispersion r > v or r < v.

Pleochroism (x):

yellow, buff, light brown, pale greenish brown, or pale greenish brown.

Pleochroism (y):

reddish brown, brown, greenish brown, bluish green, or opaque.

Calculated Properties of Biotite

Electron Density:

Bulk Density (Electron Density)=3.07 gm/cc
note: Specific Gravity of Biotite =3.10 gm/cc.

Fermion Index:

Fermion Index = 0.02
Boson Index = 0.98

Photoelectric:

PE_Biotite= 4.04 barns/electron
U=PE_Biotite x r_electron= 12.42 barns/cc.

Radioactivity:

GRapi = 129.08 (Gamma Ray American Petroleum Institute Units)
Concentration of Biotite per GRapi unit = 0.77 (%)

Estimated Radioactivity from Biotite - barely detectable

Biotite Classification

Dana Class:

71.02.02b.02 (71)Phyllosilicate Sheets of Six-Membered Rings

(71.02)with 2:1 Layers

(71.02.02b)Mica Group (Biotite subgroup)

71.02.02b.01 Phlogopite KMg3(Si3Al)O10(F,OH)2 C 2/m 2/m

71.02.02b.01a Tetraferriphlogopite! KMg3FeSi3O10(OH)2 2/m

71.02.02b.01b Shirozulite! KMn3(AlSi3)O10(OH,F)2 C 2/m 2/m

71.02.02b.01c Fluorophlogopite! KMg3(AlSi3)O10F2 C 2/m 2/m

71.02.02b.02 Biotite* K(Mg,Fe)3[AlSi3O10(OH,F)2 C 2/m 2/m

71.02.02b.03 Annite KFe3AlSi3O10(OH,F)2 C 2/m 2/m

71.02.02b.03a Fluorannite! KFe3AlSi3O10F2 C 2/m 2/m

71.02.02b.04 Tetraferriannite K(Fe,Mg)3(Fe,Al)Si3O10(OH)2 C 2/m 2/m

71.02.02b.05 Siderophyllite KFe2Al(Al2Si2)O10(F,OH)2 C 2/m 2/m

71.02.02b.05a Eastonite! KMg2Al[Al2Si2O10](OH)2 2/m

71.02.02b.06 Hendricksite K(Zn,Mg,Mn)3Si3AlO10(OH)2 C 2/m 2/m

71.02.02b.07 Lepidolite K(Li,Al)3(Si,Al)4O10(F,OH)2 C 2/m,Cm Mono

71.02.02b.08 Polylithionite KLi2AlSi4O10(F,OH)2 C 2/m 2/m

71.02.02b.08a Trilithionite! KLi1.5Al1.5AlSi3O10F2 C 2/m 2/m

71.02.02b.08b Sokolovaite! CsLi2AlSi4O10F2 C 2/m, C 2 or Cm Mono

71.02.02b.09 Tainiolite KLiMg2Si4O10F2 C 2/m 2/m

71.02.02b.10 Zinnwaldite KLiFeAl(AlSi3)O10(F,OH)2 C 2/m 2/m

71.02.02b.11 Norrishite K(Mn2Li)Si4O10(O)2 C 2/m 2/m

71.02.02b.12 Masutomilite K(Li,Al,Mn)3[(Si,Al)4O10](F,OH)2 C 2/m 2/m

71.02.02b.13 Aspidolite NaMg3AlSi3O10(OH)2 C 2/m 2/m

71.02.02b.14 Wonesite (Na,K).5(Mg,Fe,Al)3(Si,Al)4O10(OH,F)2 C 2/m 2/m

71.02.02b.15 Preiswerkite NaMg2Al3Si2O10(OH)2 C 2/m 2/m

71.02.02b.16 Ephesite NaLiAl2(Al2Si2)O10(OH)2 C 2/c 2/m

71.02.02b.18 Suhailite! (NH4)Fe3(Si3Al)O10(OH)2 C 2/m? 2/m

Strunz Class:

09.EC.20 09 - SILICATES (Germanates)

09.E - Phyllosilicates

09.EC -Phyllosilicates with mica sheets, composed of tetrahedral and octahedral nets

09.EC.20 Annite KFe3AlSi3O10(OH,F)2 C 2/m 2/m

09.EC.20 Biotite* K(Mg,Fe)3[AlSi3O10(OH,F)2 C 2/m 2/m

09.EC.20 Hendricksite K(Zn,Mg,Mn)3Si3AlO10(OH)2 C 2/m 2/m

09.EC.20 Ephesite NaLiAl2(Al2Si2)O10(OH)2 C 2/c 2/m

09.EC.20 Aspidolite NaMg3AlSi3O10(OH)2 C 2/m 2/m

09.EC.20 Lepidolite K(Li,Al)3(Si,Al)4O10(F,OH)2 C 2/m,Cm Mono

09.EC.20 Preiswerkite NaMg2Al3Si2O10(OH)2 C 2/m 2/m

09.EC.20 Masutomilite K(Li,Al,Mn)3[(Si,Al)4O10](F,OH)2 C 2/m 2/m

09.EC.20 Wonesite (Na,K).5(Mg,Fe,Al)3(Si,Al)4O10(OH,F)2 C 2/m 2/m

09.EC.20 Polylithionite KLi2AlSi4O10(F,OH)2 C 2/m 2/m

09.EC.20 Phlogopite KMg3(Si3Al)O10(F,OH)2 C 2/m 2/m

09.EC.20 Norrishite K(Mn2Li)Si4O10(O)2 C 2/m 2/m

09.EC.20 Siderophyllite KFe2Al(Al2Si2)O10(F,OH)2 C 2/m 2/m

09.EC.20 Fluorannite! KFe3AlSi3O10F2 C 2/m 2/m

09.EC.20 Shirokshinite! K(NaMg2)Si4O10F2 C 2/m 2/m

09.EC.20 Zinnwaldite KLiFeAl(AlSi3)O10(F,OH)2 C 2/m 2/m

09.EC.20 Eastonite! KMg2Al[Al2Si2O10](OH)2 2/m

09.EC.20 Tetraferriannite K(Fe,Mg)3(Fe,Al)Si3O10(OH)2 C 2/m 2/m

09.EC.20 Tetraferriphlogopite! KMg3FeSi3O10(OH)2 2/m

09.EC.20 Trilithionite! KLi1.5Al1.5AlSi3O10F2 C 2/m 2/m

09.EC.20 Sokolovaite! CsLi2AlSi4O10F2 C 2/m, C 2 or Cm Mono

09.EC.20 Shirozulite! KMn3(AlSi3)O10(OH,F)2 C 2/m 2/m

09.EC.20 Suhailite! (NH4)Fe3(Si3Al)O10(OH)2 C 2/m? 2/m

09.EC.20 Fluorophlogopite! KMg3(AlSi3)O10F2 C 2/m 2/m

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Biotite

K(Mg,Fe++)3[AlSi3O10(OH,F)2
Dana No: 71.02.02b.02 Strunz No: 09.EC.20
Locality:

Notes: