Labradorite
Labradorite is an intermediate to calcic member of the plagioclase series. Labradorite, a feldspar mineral in the plagioclase series that is often valued as a gemstone and as ornamental material for its red, blue, or green iridescence. The mineral is usually gray or brown to black and need not be iridescent.
Formula (repeating unit): (Ca,Na)(Al,Si)4O8, where Ca/(Ca + Na) (% anorthite) is 50–70%
