Bixbite
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Bixbite (also known as red beryl, red emerald, or scarlet emerald) is a red variety of beryl, Be3(Al,Mn)2Si6O18. It is very rare, only known to occur in a few locations in the western United States and one in Mexico. Bixbite was named after Maynard Bixby.
Bixbite occurs in topaz-bearing rhyolites. It formed by crystallizing under low pressure and high temperature from a pneumatolitic phase along fractures or within miarolitic cavities and rhyolitic magmas near the surface. Minerals it is found with include bixbyite, quartz, orthoclase, topaz, spessartine garnet, pseudobrookite and hematite. The red color is thought to be from manganese substituting for aluminium in the beryl structure.
Gem-quality bixbite is very rare, and the largest faceted gemstones are less than three carats (600 mg) in size.