Gemstone :



Birthstone Month :

Fibrolite is not associated with any particular birthstone month.


Zodiac :

Fibrolite is not associated with any particular zodiac sign.


Chemical Symbol :



Chemical Make-up :

Fibrolite is a common variety of Sillmanite, an Aluminum Silicate. Sillmanite is a polymorph of Kyanite and Andalusite. This means that it has the same chemical formula as these minerals but it crystallizes in a different crystal system, and is therefore distinguished as a separate mineral.


History & Lore :

Sillmanite is named after the American chemist Benjamin Silliman. The name Fibrolite alludes to this stone fibrous texture.


Though Sillmanite has perfect cleavage, it does have strong toughness and good resistance to erosion. For this reason, it was used in prehistoric times to make polished axes.


In 1977 the Delaware General Assembly, acting on a proposal by the Delaware Mineralogical Society, established Sillmanite as the State Mineral of Delaware.


Availability :

Fibrolite is rare gemstone that is not commonly used for jewelry purposes. This is most likely due to the fact that most jewelers are not aware of it, let alone the consumer. For this reason prices remain relatively low


Sources :

Gem quality Fibrolite is mined in Kenya, Myanmar (Burma), Sri Lanka (Ceylon), and the United States (Idaho).


Evaluation :

Fibrolite is rated at 7 to 7.5 on Moh's Scale of Hardness and while it is a relatively hard gemstone, care should be taken to avoid hard blows or knocks because of its perfect cleavage.


Gem quality Fibrolite is found in a number of colors ranging through grey, green, greenish-blue, blue, and violet-blue. The most sought-after variety of Fibrolite is the beautiful violet-blue stones that are mined in the Mogok Stone tract of Myanmar (Burma).


Fibrolite is strongly pleochroic, meaning that a single stone displays different colorations, depending on the angle the stone is viewed at. A greyish-green variety that is mined in Sri Lanka (Ceylon), often displays chatoyancy, which is caused by very fine inclusions within the stone. When a light source is directed off these inclusions it causes a bright strip of light appear, running perpendicular to the inclusions. This strip will then glide across the surface of the stone when turned over and give the effect of a cat's eye.


Common Cuts :

Fibrolite is most often fashioned into cabochons and flat cuts. Faceted cuts are quite rare because of Fibrolites perfect cleavage. Cabochon cuts are required to exhibit any chatoyancy displayed by the stone.


Routine Enhancements :

There are no known enhancements for Fibrolite.


Care & Cleaning :

Hard blows should always be avoided with Fibrolite as this can cause the stone to cleave. As with most gemstones, Fibrolite should be kept away from household chemicals and prolonged exposure to excessive heat that can cause permanent damage to the stone. Fibrolite is best cleaned using warm soapy water and a soft brush to remove any collected dust or grease.


Fibrolite jewelry should always be stored in a fabric-lined box away from other jewelry items to avoid scratching / damage.