Paua Abalone (Haliotis iris)from New Zealand.
Paua (usually pronounced "pow-a") is the most colorful shell in the world. Shells are typically deep blue or green. Even the reddish colors turn blue when viewed from an angle. Shells are very small and their harvest and export are tightly controlled. Generally all I can get are "waste" pieces from the lip of the shell. Paua is so brilliant that it is most effective in small accents, so these small pieces aren't much of a handicap.