Tiger's eye

Tiger's eye is a quartz with inclusions of very small quartz crystals that are stained and which replace the crocidolite fiber inclusions of the gem.
The presence of the fibrous structure produce a silky sheen when the material is cut. If well cut in cabochon, it can reproduce an «eye» quite well.

If crocidolite has not been completely replaced by silica, the original grayish blue color of crocidolite remains and produces what is called hawk’s eye or falcon’s eye.