Kyawthuite

Kyawthuite (pronounced cha-too-ite) is a rare mineral with formula BiSbO4. It is a natural bismuth antimonate, in which bismuth has oxidation state +3, and antimony oxidation state +5. It is the only bismuth–antimony oxide approved as a mineral and is named for Kyaw Thu, the Burmese gemmologist who recognised the stone as unusual. The mineral is known from a single water-worn crystal that turned up in alluvium near Mogok in Myanmar and was cut into a reddish-orange gem of 1.61 carats. Because no second natural specimen has been reported, popular-science coverage often describes kyawthuite as the rarest mineral on Earth. The only known sample of kyawthuite is on display at the Natural History Museum of Los Angeles County.