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).

Name Pronunciation:

Sillimanite + Pronunciation

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

Diaphaneity:

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:

Non-fluorescent.

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
Ncalc = 1.67

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.

Calculated Properties of Sillimanite

Electron Density:

Bulk Density (Electron Density)=3.20 gm/cc
note: Specific Gravity of Sillimanite =3.24 gm/cc.

Fermion Index:

Fermion Index = 0.0083309363
Boson Index = 0.9916690637

Photoelectric:

PE_Sillimanite= 1.64 barns/electron
U=PE_Sillimanite x rElectron Density= 5.24 barns/cc.

Radioactivity:

GRapi = 0 (Gamma Ray American Petroleum Institute Units)
Sillimanite is Not Radioactive

Sillimanite Classification

Dana Class:

52.02.02a.01 (52)Nesosilicate Insular SiO4 Groups and O, OH, F, and H2O

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

(52.02.02a)Al2SiO5 (Sillimanite subgroup)

52.02.02a.01 Sillimanite Al2SiO5=Al[6]Al[4]OSiO4 P nma 2/m 2/m 2/m

52.02.02a.02 Mullite Al(42x)Si(2-2x)O(10-x)wherex=0.17to0.59 Pbam 2/m 2/m 2/m

52.02.02a.03 Boromullite! Al4.5SiB0.5O9.5 C mc2₁ mm2

Strunz Class:

09.AF.05 09 - SILICATES (Germanates)

09.A - Nesosilicates

09.AF -Nesosilicates with additional anions;

09.AF.05 Sillimanite Al2SiO5=Al[6]Al[4]OSiO4 P nma 2/m 2/m 2/m

Other Sillimanite Information

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Ask about Sillimanite here :
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Mindat.org's Discussion Groups
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Mineral Discussion Forum from Fabre Minerals - also available in Español

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

Sillimanite

Al2SiO5 = Al[6]Al[4]OSiO4
Dana No: 52.02.02a.01 Strunz No: 09.AF.05
Locality:

Notes: