Bull's eye
Bull's Eye belongs to the silicate group. It is primarily composed of silicon and has the same chemical formula as Quartz, SiO2 . It is a variety of chalcedony.
It occurs in massive microcrystalline form. It is a very hard stone. The alternating bands result from its combination with another iron-rich mineral, crocidolite, which is a variety of riebeckite. In bull's-eye, the crocidolite fibers undergo a chemical transformation into iron oxide and are replaced by silicon dioxide, resulting in a shimmering yellow color that turns reddish-brown upon heating.
There are several types of eyes: TIGER'S EYE , BULL'S EYE (most often heated Tiger's Eye), CAT'S EYE , HAWK'S EYE , IRON EYE .
