Sunstone
(Ca,Na)(Al,Si)4O8
Sunstone is an iridescent variety of plagioclase feldspar containing tiny oriented platelets of copper or hematite that produce a metallic sparkle (aventurescence). Oregon and Norway are the classic sources.
Sunstone is the gem variety of feldspar that shows aventurescence — a warm, metallic, glittering sparkle caused by light reflecting from countless tiny plate-like inclusions. In most sunstone the platelets are hematite or goethite; in the celebrated Oregon material they are microscopic flakes of native copper.
Properties
Sunstone may be a plagioclase (oligoclase to labradorite) or, less commonly, a potassium feldspar; it is hard (6–6.5) with the two good cleavages typical of feldspars. Oregon sunstone is prized because the copper also produces body colours from yellow through pink to rare green and the 'red' stones, sometimes with colour zoning.
Occurrence
Sources include Oregon in the United States, Norway (the historic locality), India, Tanzania and Russia. Aventurescent labradorite from several countries is also sold as sunstone.