sillimanite
fibrolite variety from Burma
solid like inclusions : rutile needle or hyperstene
detail of white needles
Detailed sheet
sillimanite
Discovered in 1824, it honors the name of the American geologist Benjamin Silliman (1779-1864).
It is also known for its blue or violet variety called fibrolite. It has been known since prehistoric times and it was used to manufacture cutting tools.
There is also a purplish brown iridescent variety.
The sillimanite is polymorphic with andalusite and kyanite, it has the same chemical composition but the shape of its crystals is different.
CHEMICAL CHARACTERISTICS
Al2[SiO5]
alumino silicate
PHYSICAL CHARACTERISTICS
Main color
white
Other colors
blue, brown, grey, yellow, green, purple
Color of streak
white
Luster
vitreous
Hardness
6.5 to 7.5
Density
3.23 to 3.28
Cleavage
perfect
Fracture
uneven
on the fracture, presence of elongated planar portions
OPTICAL PROPERTIES
Transparency
transparent
the shimmering variety is opaque
Refractive index
1.655 - 1.684
Double refraction
0.014
definite, biaxial (+)
visible double refraction
Yes
Dispersion
0,015(0.010)
Pleochroism
strong
Number of colors
2
colorless, colored
Absorption spectrum
462 - 441 - 410
Fluorescence
variable
sometimes yellow - orange
CRYSTALS PROPERTIES
prismatic
crystals system
orthorhombic
OTHER INFORMATIONS
APPROACHING GEMS
Exploited
sites
It is found in Tanzania (Arusha), Brazil (Goias), Australia (Tasmania, Queensland), China (Manchuria), United States, Alaska (Port Clarence), New Hampshire, Connecticut, Pennsylvania, New Jersey, North Carolina, Colorado, and Mogok in Burma and India.
use in jewelry
it is cut faceted when it is transparent and cabochon in its iridescent variety. The blue or purple varieties from Mogok in Burma or Sri Lanka are the most popular.
Daily care
and precautions
Quite easy maintenance, cleaning with dish detergent and then rinsing with soft water.
Other
Gems
Venez visitez
notre site web
voillot-joaillier.fr
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