Ivory

Piano keys were originally reversed from todays layout. In the era of Mozart and Beethoven, the wide keys were black and the narrow keys were white. This was likely because ivory, used for white keys, was more expensive than ebony used for black keys.

An elephant's tusks are not molars but massively overgrown upper incisors — front teeth. The Chinese characters for ivory use the character for "molar," adding to the misconception, but anatomically tusks grow from the front of the jaw.