Are these gemstones the same?
What is the difference between Fibrolite and Sillimanite? Well, in 1802 a man called Mr Bournon named a mineral with a chemical composition AI2SiO5 as Fibrolite, then as far as I can work out in 1824 for no apparent reason at all, a Mr G. T. Bowen decided to change its name to Sillimanite, after the American chemist Benjamin Silliman!
So, why in this book do we have two headings, one for Sillimanite and one for Fibrolite? Well, I debated for a while whether to combine the two, however, as the industry tends to name pieces which show chatoyancy as Fibrolite Cat’s Eye and those that don’t as Sillimanite, I decided to document them separately.
Some gemmologists view Fibrolite as a common variety of Sillimanite. Fibrolite’s name seems to come from the fact that this mineral looks like fibres twisted together.
A small parcel of Fibrolite Cat’s Eye that I recently acquired for GemCollector.com contains nice translucent brownish yellow cabochon cut gems from Sri Lanka, which range from just under 3 carats to over 4.5 carats.
Gem-quality Fibrolite has also been found in Kenya, Burma and Idaho,USA.