This hefty, sharp "mica book" is a cleavage portion of a larger original crystal, preserving the outer faces but (as with all such) showing faces on the front and back that are cleaved. It weighs 2.6 pounds! From the noted Clarence S. Bement (1843-1923) Collection. Given the early accession number, and the future fate of his collection going to the AMNH in the 1900s, this was certainly obtained from him personally before his death and the purchase (followed by donation elsewhere) of the rest of his collection by financier JP Morgan.