Sillimanite Mineral Data

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General Sillimanite Information

Chemical Formula:

Al2SiO5 = Al[6]Al[4]OSiO4

Composition:

Molecular Weight = 162.05 gm

Aluminum 33.30 % Al 62.92 % Al₂O₃

Silicon 17.33 % Si 37.08 % SiO₂

Oxygen 49.37 % O

______ ______

100.00 % 100.00 % = TOTAL OXIDE

Empirical Formula:

(Al₂O₃)(SiO₂)

Environment:

Metamorphosed peri-aluminous sedimentary rocks.

IMA Status:

Valid Species (Pre-IMA) 1824

Locality:

Wide spread world wide occurrences. Link to MinDat.org Location Data.

Name Origin:

Named after the American chemist and mineralogist, B. Silliman (1779-1824).

Synonym:

Fibrolite

ICSD 100450

PDF 38-471

Sillimanite Image

Images:

Sillimanite

Comments: Silky massive sillimanite.
Location: Khasia Hills, Assum, India. Scale: See Photo.
© Jeff Weissman / Photographic Guide to Mineral Species

Sillimanite Crystallography

Axial Ratios:

a:b:c =0.9754:1:0.752

Cell Dimensions:

a = 7.484, b = 7.672, c = 5.77, Z = 4; V = 331.30 Den(Calc)= 3.25

Crystal System:

Orthorhombic - DipyramidalH-M Symbol (2/m 2/m 2/m) Space Group: P nma

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

By Intensity(I/I_o): 3.42(1), 3.37(0.65), 2.2(0.6),

Forms:

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Forms: [ 1 2 0] [ 2 1 0] [ 1 1 0] [ 1 0 0] [ 0 0 1]

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Crystal Structure:

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Winter J K , Ghose S , American Mineralogist , 64 (1979) p.573-586, Thermal expansion and high-temperature crystal chemistry of the Al2SiO5, polymorphs, T = 25 deg C

View Additional jPOWD Structure files for Sillimanite
[1] [10] [11] [12] [13] [14] [15] [16] [2] [3] [4] [5] [6] [7] [8] [9]

Physical Properties of Sillimanite

Cleavage:

[010] Perfect

Color:

Bluish, Brownish greenish, Colorless, Gray, Gray green.

Density:

3.24

Diaphaniety:

Transparent to translucent

Fracture:

Splintery - Thin, elongated fractures produced by intersecting good cleavages or partings (e.g. hornblende).

Habit:

Acicular - Occurs as needle-like crystals.

Habit:

Fibrous - Crystals made up of fibers.

Habit:

Prismatic - Crystals Shaped like Slender Prisms (e.g. tourmaline).

Hardness:

7 - Quartz

Luminescence:

None.

Luster:

Vitreous (Glassy)

Streak:

white

Optical Properties of Sillimanite

Gladstone-Dale:

CI meas= 0.01 (Superior) - where the CI = (1-KPDmeas/KC)
CI calc= 0.013 (Superior) - where the CI = (1-KPDcalc/KC)
KPDcalc= 0.2047,KPDmeas= 0.2053,KC= 0.2074

Optical Data:

Biaxial (+), a=1.653-1.661, b=1.654-1.67, g=1.669-1.684, bire=0.0160-0.0230, 2V(Calc)=30-80, 2V(Meas)=20-30. Dispersion strong, r > v.

Pleochroism (x):

colorless, pale brown, or yellow.

Pleochroism (y):

colorless, brown, or grayish green.

Pleochroism (z):

colorless, brown, or blue.

Calculated Properties of Sillimanite

Electron Density:

r_electron=3.20 gm/cc
note: r_Sillimanite=3.24 gm/cc.

Fermion Index

Fermion Index = 0.00833
Boson Index = 0.99167

Photoelectric:

PE_Sillimanite= 1.64 barns/electron
U=PE_Sillimanite x r_electron= 5.24 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)

Sillimanite is Not Radioactive

Sillimanite Classification

Dana Class:

52.2.2a.1 (52)Nesosilicate Insular SiO4 Groups and O, OH, F, and H2O

(52.2)with cations in [4] and >[4] coordination

(52.2.2a)Al2SiO5 (Sillimanite subgroup)

52.2.2a.1 Sillimanite Al2SiO5=Al[6]Al[4]OSiO4 P nma 2/m 2/m 2/m

52.2.2a.2 Mullite Al(42x)Si(2-2x)O(10-x)wherex=0.17to0.59 Pbam 2/m 2/m 2/m

Strunz Class:

VIII/B.02-10 VIII - Silicates

VIII/B - Nesosubsilicates, with anions unfamiliar to tetraheders, cations of octahedral and tetrahedral orientation [4/6]

VIII/B.02 - Disthene series

VIII/B.02-10 Sillimanite Al2SiO5=Al[6]Al[4]OSiO4 P nma 2/m 2/m 2/m

VIII/B.02-20 Andalusite Al2SiO5=Al[6]Al[5]OSiO4 Pnnm 2/m 2/m 2/m

VIII/B.02-30 Kanonaite (Mn,Al)AlSiO5 Pnnm 2/m 2/m 2/m

VIII/B.02-40 Kyanite Al2SiO5=Al[6]Al[6]OSiO4 P1 1

VIII/B.02-50 Mullite Al(42x)Si(2-2x)O(10-x)wherex=0.17to0.59 Pbam 2/m 2/m 2/m

VIII/B.02-60 Yoderite Mg2(Al,Fe)6Si4O18(OH)2 P 2₁ 2

VIII/B.02-70 Topaz Al2SiO4(F,OH)2 Pbnm 2/m 2/m 2/m

Other Sillimanite Information

References:

NAME( Duda&Rejl90) PHYS. PROP.(Enc. of Minerals,2nd ed.,1990) OPTIC PROP.(Heinrich65)

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Print or Cut-and-Paste your Sillimanite Specimen Label here :

Sillimanite

Al2SiO5 = Al[6]Al[4]OSiO4
Dana No: 52.2.2a.1 Strunz No: VIII/B.02-10
Locality:

Notes: