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Sillimanite

Nesosilicate mineral

Summary

Nesosilicate mineral

Field	Value
name	Sillimanite
category	Nesosilicate
image	Sillimanite-k302a.jpg
formula	Al2SiO5
IMAsymbol	Sil
strunz	9.AF.05
dana	52.02.02a.01
system	Orthorhombic
class	Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
symmetry	Pbnm
unit cell	a = 7.47 Å, b = 7.66 Å
c = 5.75 Å; Z = 4
color	Colourless or white to grey, also brown, yellow, yellow-green, grey-green, blue-green, blue; colourless in thin section
habit	Prismatic crystals, fibrous, acicular
cleavage	{010} perfect
fracture	Splintery
tenacity	Tough
mohs	7
luster	Vitreous to subadamantine, silky
streak	White
diaphaneity	Transparent to translucent
gravity	3.24
opticalprop	Biaxial (+)
refractive	nα = 1.653 – 1.661 nβ = 1.654 – 1.670 nγ = 1.669 – 1.684
birefringence	δ = 0.020 – 0.022
pleochroism	Colourless to pale brown to yellow
2V	21–30°
references

H-M symbol: (2/m 2/m 2/m) c = 5.75 Å; Z = 4 | length fast/slow = Sillimanite or fibrolite is an aluminosilicate mineral with the chemical formula Al2SiO5. Sillimanite is named after the American chemist Benjamin Silliman (1779–1864). It was first described in 1824 for an occurrence in Chester, Connecticut.

Occurrence

Sillimanite or fibrolite is one of three aluminosilicate polymorphs, the other two being andalusite and kyanite. A common variety of sillimanite is known as fibrolite, so named because the mineral appears like a bunch of fibres twisted together when viewed in thin section or even by the naked eye. Both the fibrous and traditional forms of sillimanite are common in metamorphosed sedimentary rocks. It is an index mineral indicating high temperature but variable pressure. Example rocks include gneiss and granulite. It occurs with andalusite, kyanite, potassium feldspar, almandine, cordierite, biotite and quartz in schist, gneiss, hornfels and also rarely in pegmatites.

Sillimanite has been found in Brandywine Springs, New Castle County, Delaware. It was named by the State Legislature in 1977 as the state mineral of Delaware by the suggestion of the Delaware Mineralogical Society.

Uses

Natural sillimanite is used in the manufacture of high alumina refractories or 55–60% alumina bricks. However, it has mostly been replaced by the other aluminosilicate polymorphs, andalusite and kyanite, for this purpose. , sillimanite was just 2% of all aluminosilicate mineral production in the western world.

Gallery

File:Sillimanite.jpg|Silimanite crystal from Sri Lanka File:Fibrolite.JPG|Fibrolite micrograph

References

Warr, L.N.. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine.
"WebMineral entry".
http://rruff.geo.arizona.edu/doclib/hom/sillimanite.pdf Handbook of Mineralogy
http://www.mindat.org/min-3662.html Mindat.org
(1980). "Atlas of rock-forming minerals in thin section". Longman Scientific & Technical.
0-471-80580-7
"Delaware State Mineral – Delaware Geological Survey".
(1977). "Alumino-Silicate Refractories". Fuels, Furnaces and Refractories.
(2000). "Utilisation of sillimanite minerals, their geology, and potential occurrences in Norway – an overview". Geological Survey of Norway Bulletin.

Wikipedia Source

This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page.

aluminium-minerals nesosilicates orthorhombic-minerals minerals-in-space-group-62 industrial-minerals symbols-of-delaware

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