Tigers Eye Rough
Tigers Eye, a member of the Quartz group, has long been a popular mineral for rock tumbling. The shifting light bands that make it so popular are caused by light reflecting off of parallel strands of silica. Tigers Eye is usually a metamorphic rock where silica, over time, replaces fibrous crocidolite in the original mineral. Incomplete silicification leads to a blue variant called Hawks Eye.
Tigers Eye is a fantastic example of a pseudomorphic mineral. A pseudomorph is a mineral or compound that exhibits atypical characteristics borrowed from a mineral it replaces - think Invasion of the Body Snatchers. In the case of Tigers Eye the crocidolite fibers are replaced by silica which maintains the fibrous structure of the crocidolite.
Tigers Eye polishes up beautifully, is a hit with the kids and apparently wards off the evil eye.