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Benjamin Silliman
Colorless, white, yellow, brown, green, gray.
Sub-Vitreous, Greasy, Silky
6½ - 7½
Specific Gravity:
3.23 - 3.27
Crystal System:
Named by George Thomas Bowen in 1824 in honor of Benjamin Silliman, Sr. (August 8, 1779, North Stratford (Trumbull), Connecticut, USA - November 24, 1864, New Haven, Connecticut, USA), Professor of Chemistry and Geology, Yale University, New Haven, Connecticut, USA, and founder of the American Journal of Science (Silliman's Journal).
Polymorph of:
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Classification of SillimaniteHide

Approved, 'Grandfathered' (first described prior to 1959)

9 : SILICATES (Germanates)
A : Nesosilicates
F : Nesosilicates with additional anions; cations in [4], [5] and/or only [6] coordination

52 : NESOSILICATES Insular SiO4 Groups and O,OH,F,H2O
2 : Insular SiO4 Groups and O, OH, F, and H2O with cations in [4] and >[4] coordination

15 : Silicates of Aluminum

Pronounciation of SillimaniteHide

PlayRecorded byCountry
Jolyon & Katya RalphUnited Kingdom

Physical Properties of SillimaniteHide

Sub-Vitreous, Greasy, Silky
Transparent, Translucent
Colorless, white, yellow, brown, green, gray.
Ideally colorless, inclusions and stains are responsible for other colors.
6½ - 7½ on Mohs scale
{010} perfect
Usually fibrous due to breakage along fiber boundaries.
3.23 - 3.27 g/cm3 (Measured)    3.24 g/cm3 (Calculated)

Optical Data of SillimaniteHide

Biaxial (+)
RI values:
nα = 1.653 - 1.661 nβ = 1.654 - 1.670 nγ = 1.669 - 1.684
Measured: 20° to 30°, Calculated: 30° to 80°
Max Birefringence:
δ = 0.016 - 0.023
Image shows birefringence interference colour range (at 30µm thickness)
and does not take into account mineral colouration.
Surface Relief:
r > v strong
Optical Extinction:
Parallel. XYZ=abc
May be seen in colored varieties, but only in thick sections. X=pale yellow Y=brown or light green Z=dark brown or blue

Chemical Properties of SillimaniteHide

IMA Formula:
Common Impurities:

Crystallography of SillimaniteHide

Crystal System:
Class (H-M):
mmm (2/m 2/m 2/m) - Dipyramidal
Cell Parameters:
a = 7.484 Å, b = 7.672 Å, c = 5.770 Å
a:b:c = 0.975 : 1 : 0.752
Unit Cell V:
331.30 ų (Calculated from Unit Cell)
Usually fibrous in wavy bundles. Rarely in well defined rectangular to square cross-sectioned prisms.

X-Ray Powder DiffractionHide

Image Loading

Radiation - Copper Kα
Data Set:
Data courtesy of RRUFF project at University of Arizona, used with permission.
Powder Diffraction Data:
3.84 (10)
3.42 (100)
3.37 (40)
2.68 (20)
2.54 (20)
2.42 (20)
2.20 (30)
1.520 (10)
ICDD 38-471

Type Occurrence of SillimaniteHide

General Appearance of Type Material:
White to light yellow stained fibers in biotite schist with quartz segregations.
Geological Setting of Type Material:
Metasedimentary rocks
Associated Minerals at Type Locality:

Synonyms of SillimaniteHide

Other Language Names for SillimaniteHide

Varieties of SillimaniteHide

FibroliteA name for the fibrous form of sillimanite. Fibrolite is generally white to pale yellow and may be if parallel bundles of fibers that seem to conformat to the geometry of adjacent minerals, often in a gentle sweep of bent crystals. Fibrolite, is by far, t...

Common AssociatesHide

BiotiteA series or subgroup of the Mica Group.
Associated Minerals Based on Photo Data:
Biotite21 photos of Sillimanite associated with Biotite on
Quartz16 photos of Sillimanite associated with Quartz on
Almandine15 photos of Sillimanite associated with Almandine on
Prismatine8 photos of Sillimanite associated with Prismatine on
Muscovite7 photos of Sillimanite associated with Muscovite on
Andalusite6 photos of Sillimanite associated with Andalusite on
Corundum6 photos of Sillimanite associated with Corundum on
Cordierite5 photos of Sillimanite associated with Cordierite on
Fibrolite5 photos of Sillimanite associated with Fibrolite on
Pyrite5 photos of Sillimanite associated with Pyrite on

Related Minerals - Nickel-Strunz GroupingHide

9.AF.10AndalusiteAl2(SiO4)OOrth. mmm (2/m 2/m 2/m) : Pnnm
9.AF.10KanonaiteMn3+Al(SiO4)OOrth. mmm (2/m 2/m 2/m) : Pnnm
9.AF.15KyaniteAl2(SiO4)OTric. 1 : P1
9.AF.20MulliteAl4+2xSi2-2xO10-xOrth. mmm (2/m 2/m 2/m) : Pbam
9.AF.20Krieselite(Al,Ga)2(GeO4)(OH)2Orth. mmm (2/m 2/m 2/m) : Pnma
9.AF.23BoromulliteAl9BSi2O19Orth. mm2 : Cmc21
9.AF.25YoderiteMg(Al,Fe3+)3(SiO4)2O(OH)Mon. 2/m : P21/m
9.AF.30MagnesiostauroliteMg(Mg,Li)3(Al,Mg)18Si8O44(OH)4Mon. 2/m : B2/m
9.AF.30StauroliteFe2+2Al9Si4O23(OH)Mon. 2/m : B2/m
9.AF.30ZincostauroliteZn2Al9Si4O23(OH)Mon. 2/m : B2/m
9.AF.35TopazAl2(SiO4)(F,OH)2Orth. mmm (2/m 2/m 2/m)
9.AF.40NorbergiteMg3(SiO4)(F,OH)2Orth. mmm (2/m 2/m 2/m)
9.AF.45AlleghanyiteMn2+5(SiO4)2(OH)2Mon. 2/m : P21/b
9.AF.45Chondrodite(Mg,Fe2+)5(SiO4)2(F,OH)2Mon. 2/m : P21/b
9.AF.45ReinhardbraunsiteCa5(SiO4)2(OH,F)2Mon. 2/m : P21/b
9.AF.45KumtyubeiteCa5(SiO4)2F2Mon. 2/m : P21/b
9.AF.45HydroxylchondroditeMg5(SiO4)2(OH)2Mon. 2/m : P21/b
9.AF.50Humite(Mg,Fe2+)7(SiO4)3(F,OH)2Orth. mmm (2/m 2/m 2/m)
9.AF.50Unnamed (Ca-analogue of Humite)Ca7(SiO4)4F2Orth. mmm (2/m 2/m 2/m)
9.AF.55ClinohumiteMg9(SiO4)4F2Mon. 2/m : P21/b
9.AF.55HydroxylclinohumiteMg9(SiO4)4(OH)2Mon. 2/m
9.AF.60LeucophoeniciteMn2+7(SiO4)3(OH)2Mon. 2/m : P21/b
9.AF.70JerrygibbsiteMn2+9(SiO4)4(OH)2Orth. mmm (2/m 2/m 2/m) : Pbcn
9.AF.75WeliniteMn2+6(W6+,Mg)2(SiO4)2(O,OH)6Trig. 3 : P3
9.AF.85Chloritoid(Fe2+,Mg,Mn2+)Al2(SiO4)O(OH)2Mon. 2/m : B2/b
9.AF.85MagnesiochloritoidMgAl2(SiO4)O(OH)2Mon. 2/m : B2/b
9.AF.90PoldervaartiteCaCa[SiO3(OH)](OH)Orth. mmm (2/m 2/m 2/m) : Pbca
9.AF.90OlmiiteCaMn2+[SiO3(OH)](OH)Orth. mmm (2/m 2/m 2/m) : Pbca

Related Minerals - Hey's Chemical Index of Minerals GroupingHide

15.1AndalusiteAl2(SiO4)OOrth. mmm (2/m 2/m 2/m) : Pnnm
15.2KyaniteAl2(SiO4)OTric. 1 : P1
15.4MulliteAl4+2xSi2-2xO10-xOrth. mmm (2/m 2/m 2/m) : Pbam
15.5PyrophylliteAl2Si4O10(OH)2Tric. 1
15.6DickiteAl2(Si2O5)(OH)4Mon. m : Bb
15.7NacriteAl2(Si2O5)(OH)4Mon. m : Bb
15.8KaoliniteAl2(Si2O5)(OH)4Tric. 1 : P1
15.10HalloysiteAl2(Si2O5)(OH)4Mon. m : Bb
15.11Allophane(Al2O3)(SiO2)1.3-2 · 2.5-3H2OAmor.

Fluorescence of SillimaniteHide

Not fluorescent.

Other InformationHide

Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.
Industrial Uses:
Used as a source for synthesizing high-temperature industrial ceramics.

Sillimanite in petrologyHide

An essential component of rock names highlighted in red, an accessory component in rock names highlighted in green.

References for SillimaniteHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Bowen, G.T. (1824) American Journal of Science: 8: 113.
Clark, S.P., Robertson, E.C., Birch, F. (1957) Experimental determination of kyanite-sillimanite equilibrium relations at high temperatures and pressure: American Journal of Science: 255: 628-640.
Pearson, G.R., Shaw, D.M. (1960) Trace elements in kyanite, sillimanite and andalusite. American Mineralogist: 45: 808-817.
Burnham, C.W. (1963) Refinement of the crystal structure of sillimanite. Zeitschrift für Kristollographie: 118: 127-148.
Chinner, G.A., Smith, J.W., Knowles, C.R. (1969) Transition metal contents of Al2SiO5 polymorphs: American Journal of Science: 267A: 96-113.
Raymond, M., Hafner, S.S. (1970) Nuclear quadrupole coupling tensors of 27 Al in sillimanite Al2SiO5). Journal of Chemical Physics: 53: 4110-4111.
Finger, L.W., Prince, E. (1972) Neutron diffraction studies: andalusite and sillimanite. Carnegie Institution of Washington, Year Book: 71: 496-500.
Vaughan, M.T., Weidner, D.J. (1978) The relationship of elasticity and crystal structure in andalusite and sillimanite. Physics and Chemistry of Minerals: 3: 133-144.
Vernon, R.H. (1979) Formation of late sillimanite by hydrogen metasomatism (base-leaching) in some high-grade gneisses. Lithos: 12: 143-152.
Winter, J.K., Ghose, S. (1979) Thermal expansion and high-temperature crystal chemistry of the Al2SiO5 polymorphs. American Mineralogist: 64: 573-586.
Grew, E.S. (1980) Sillimanite and ilmenite from high-grade metamorphic rocks of Antarctica and other areas. Journal of Petrology: 21: 39-68.
Fleet, M.E., Arima, M. (1985) Oriented hematite inclusions in sillimanite. American Mineralogist: 70: 1232-1237.
Grew, E.S., Rossman, G.R. (1985) Co-ordination of boron in sillimanite. Mineralogical Magazine: 49: 132-135.
Vernon, R.H., Flood, R.H., D'Arcy, W.F. (1987) Sillimanite and andalusite produced by base-cation leaching and contact metamorphism of felsic igneous rocks. Journal of Metamorphic Geology: 5: 439-450.
Kerrick, D.M. (1990) Metamorphic reactions. In D.M. Kerrick, Ed., The Al2SiO5 polymorphs. 22, 223-253. Reviews in Mineralogy. Mineralogical Society of America, Chantilly, Virginia.
Kerrick, D.M. (1990) The Al2SiO5 polymorphs, 22, 406 p. Reviews in Mineralogy, Mineralogical Society of America, Chantilly, Virginia.
Bish, D.L., Burnham, C.W. (1992) Rietveld refinement of the crystal structure of fibrolitic sillimanite using neutron powder diffraction data. American Mineralogist: 77: 374-379.
Yang, H., Hazen, R.M., Finger, L.W., Prewitt, C.T., Downs, R.T. (1997) Compressibility and crystal structure of sillimanite, Al2SiO5, at high pressure. Physics and Chemistry of Minerals: 25: 39-47.
Rao, M.N., Chaplot, S.L., Choudhury, N., Rao, K.R., Azuah, R.T., Montfrooji, W.T., Bennington, S.M. (1999) Lattice dynamics and inelastic neutron scattering from sillimanite and kyanite Al2SiO5. Physical Review: B60: 12061.
Dahaoui, S., Ghermani, N.E., Ghose, S., Howard, J.A.K. (2001) Electric field gradient tensors at the aluminum sites in the Al2SiO5 polymorphs from CCD high-resolution X-ray diffraction data: comparison with 27 Al NMR results. American Mineralogist: 86: 159-164.
Iglesias, M., Schwarz, K., Blaha, P., Baldomir, D. (2001) Electronic structure and electric field gradient calculations of Al2SiO5 polymorphs. Physics and Chemistry of Minerals: 28: 67-75.
Winkler, B., Hytha, M., Warren, M.C., Milman, V., Gale, J.D., Schreuer, J. (2001) Calculation of the elastic constants of the Al2SiO5 polymorphs andalusite, sillimanite, and kyanite. Zeitschrift für Kristallographie: 216: 67-70.
Friedrich, A., Kunz, M., Winkler, B., Le Bihan T. (2004) High-pressure behavior of sillimanite and kyanite: compressibility, decomposition and indications of a new high-pressure phase. Zeitschrift für Kristallographie: 219: 324-329.
Burt, J.B., Ross, N.L., Angel, R.J., Koch, M. (2006) Equations of state and structures of andalusite to 9.8 GPa and sillimanite to 8.5 GPa. American Mineralogist: 91: 319-326.
Ohuchi, F.S., Ghose, S., Engelhard, M.H., Baer, D.R. (2006) Chemical bonding and electronic structures of the Al2SiO5 polymorphs, andalusite, sillimanite, and kyanite: X-ray photoelectron- and electron energy loss spectroscopy studies. American Mineralogist: 91: 740-746.

Internet Links for SillimaniteHide

Localities for SillimaniteHide

This map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.

Locality ListShow