Crocidolite - Encyclopedia

    Class : Silicates
    Subclass : Inosilicates
    Crystal system : Monoclinic
    Chemistry : Na₂Fe₅Si₈O₂₂(OH)₂
    Rarity : Uncommon

Crocidolite is an asbestiform variety of riebeckite, an alkaline amphibole which forms a series with glaucophane. It is a chatoyant blue variety, changing to golden yellow-brown by iron oxidation, which is mainly found in metamorphic environments, particularly in metamorphosed banded iron formations (BIF). Its name comes from the Greek krokus (fiber) and lithos (stone) because of its fibrous morphology. Crocidolite is one of the minerals used industrially under the name of asbestos : it is blue asbestos. It is also used in ornamentation and jewelry under the name tiger's eye and hawk's eye.

Main photo : Hawk's eye cabochon (unoxidized crocidolite) from South Africa

No known twin for this mineral variety.

No fakes listed for this mineral variety which is very abundant on the market and inexpensive. The chatoyancy can be imitated by fiber optics, but the plastic appearance doesn't fool many people...

On the other hand, tiger's eye and hawk's eye are widely treated by heating because they give a brown-red color whose commercial name is bull's eye.

In order to offer more colors for the market, tiger's eye is also sometimes dyed in pink, intense blue, green, etc... these colors do not exist in Nature.