Blue Abalone also know as green abalone or Haliotis Fulgens is an interesting shell, found with a dull brownish exterior and a iridescent blue-green interior with several natural holes.  Found near the coast of California and Mexico they are often considered a delicacy among seafood connoisseurs. 

commonly used as a natural incense burner or for its beautiful mother of pearl blue-green interior  broken up for jewelry crafting/ inlaying