Fibrolite (Sillimanite)
SLM120, Sillimanite, Fibrolite, [N], 12.2mm Cabochon, Round Cut, 5.52 ct. $ 69.99
SLM121, Sillimanite, Fibrolite, [N], 10.9x11.2mm Cabochon, Round Cut, 9.12 ct. $ 114.99 ...
beryl, apatite, fibrolite and tourmaline cat's eyes
Blue Sapphire
tourmaline (indicolite), blue Spinel and amethyst ...
Comments: appearance & RI almost identical to fibrolite, distinguish by lower SG. Fauslite... see turquoise
Comments: turquoise which zinc is the colorent Feldspar ...
My previous article initiated a series on polymorphic aluminum silicate gemstones, beginning with andalusite, following with kyanite (disthene) and ending with sillimanite (fibrolite).
Sillimanite is a very rare trimorph and it has a common variety called fibrolite. Usually the bigger crystals of Sillimanite are hard with a hardness of 7.5 and the fibrous varieties are comparatively softer.
Kyanite has a similar chemical composition to andalusite and fibrolite, but it has a different crystal structure. Kyanite exhibits a small range of colors including blue, colorless, blue-green, and brown.
Sillimanite is sometime referred to as fibrolite. Sillimanite is not only scarce, but also difficult for miners to identify and problematic for cutters. These three attributes combine to ensure that sillimanite remains a true exotic gemstone.
Sometimes referred to as "Fibrolite", the crystals occur in groups, resembling fibers. Sillimanite is a transparent to translucent mineral that ranges in color from white to gray to brownish to greenish.
Sillimanite is named after an American chemist and mineralogist, Prof. Benjamin Silliman. For its fibrous inclusions, it is sometimes also known as "fibrolite" in the jewelry world.
 See also: Crystal, Gemstone, Color, Stone, Crystals
  
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