Common name for a variety of quartz which is chatoyant because of parallel intergrowth of quartz crystals and altered amphibole fibres that mostly turned into limonite. Much used as an ornamental and lapidary rock. A new interpretation of the origin of tiger's eye was recently given by Heaney and Fisher (2003): "Tiger's-eye is an attractive and popular gemstone that is ubiquitous in stores that cater to rock and mineral collectors. For more than a century, textbooks and museum displays have identified the material as an archetype of pseudomorphism, i.e., the replacement of one mineral by another with the retention of the earlier mineral's shape. Our study has revealed that the textures responsible for the shimmer of tiger's-eye do not represent pseudomorphic substitution of quartz after preexisting crocidolite asbestos. Rather, we argue that tiger's-eye classically exemplifies synchronous mineral growth through a crack-seal vein-filling process."