The hard dentine that forms the elongated tusks of elephants and some other animals; long used for ornaments, its international trade is now largely banned.
Piano keys once had the opposite color layout. In the era of Mozart and Beethoven, wide keys were black and narrow keys white. This was likely because ivory for white keys cost more than ebony 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.