NATURAL HISTORY MUSEUM, LONDON / SCIENCE PHOTO LIBRARY NATURAL HISTORY MUSEUM, LONDON / SCIENCE PHOTO LIBRARY
Tiger's eye and hawk's eye gemstones. These gemstones are formed when the mineral crocidolite (blue asbestos) is replaced by quartz. Hawk's eye (bottom) retains the original blue colour while tiger's eye (top) contains a residue of iron oxide, forming a golden to red-brown colour.
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