What is a hard, black variety of vulcanite. It may be cut and polished, and is used for many small articles, as combs and buttons, and for insulating material in electric apparatus called?

ebonite — A hard, black variety of vulcanite. It may be cut and polished, and is used for many small articles, as combs and buttons, and for insulating material in electric apparatus. (Webster's 1913.)

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