Silicon Carbide    Probably a General Electric product.  Ex. Harold Dibble collection.  These attractive, man-made crystals represent the finest, large cluster I have owned.  They are up to 4 cm across an the specimen is 12.5 x 10.5 x 9.5 cm.  One crystal shows some breakage but overall the piece is in excellent condition.  This is a variety of corundum and usually used as an abrassive.  $250