“Commodity” means, except as otherwise specified by the commissioner by rule or order, any agricultural, grain, or livestock product or byproduct, any metal or mineral (including a precious metal set forth in Section 29515), any gem or gemstone (whether characterized as precious, semiprecious, or otherwise), any fuel (whether liquid, gaseous, or otherwise), any foreign currency, and all other goods, articles, products, or items of any kind. However, the term “commodity” shall not include (a) a numismatic coin whose fair market value is at least 15 percent higher than the value of the metal it contains, or (b) any work of art offered or sold by art dealers, at public auction, or through a private sale by the owner of the work of art.