What is a hydrate of alumina, often occurring in white lamellar masses with brilliant pearly luster; -- so named on account of its decrepitating when heated before the blowpipe called?

diaspore — A hydrate of alumina, often occurring in white lamellar masses with brilliant pearly luster; -- so named on account of its decrepitating when heated before the blowpipe. (Webster's 1913.)

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