Fuchsite, K(AlCr)2(AlSi3)O10(OH)2, is hydrous potassium aluminum silicate. Fuchsite is a variety of muscovite, a type of mica, with up to 4.8% chromium oxide. Chromium is what gives fuchsite its bright emerald green color.
The presence of fuchsite in the Earth usually indicates there are peridot serpentine rocks nearby. Fuchsite’s primary use is its interest to scientists and collectors.