brittle, translucent, semiprecious chalcedony (q.v.), a variety of the silica mineral quartz. It owes its bright apple-green colour to colloidally dispersed hydrated nickel silicate; heating or prolonged exposure to sunlight will cause the colour to fade. Its physical properties are those of quartz (see silica mineral 【table】 ). Typical occurrences are in serpentine as a secondary mineral found in cavities and veins; California and Silesia have notable deposits. Imitation chrysoprase is chalcedony dyed with nickel or chromium salts.