Nevada is famous for its beautiful, colorful black Opal. The state contains some very rich precious opal beds and has produced some spectacular and extremely valuable specimens.  The Virgin Valley opal beds in northwest Humboldt County are perhaps the most famous gemstone locality in Nevada. High quality precious opal emitting a multihued rainbow of color is found replacing wood or other plant material in this remote location.  […]

Source:  https://www.geologyin.com/2017/04/rare-fossil-wood-precious-opal-from.html