320 CLAY GENUS. Fragments indeterminately angular, blunt edged. Soft, palling to friable. Light. Although Werner has given the preceding de- fcription as that of alumituue, he does not venture to affirm that he has defcribed the true Roman alum ftone, as it is extremely difficult to procure fpecimens of it, its exportation oemg forbidden by the moft fevere punilhments. Geographic Situation. It is found at Tolta near Rome, where it is faid to form a whole hill. Werner has alto a fpecim en which is faid to have been found in Hungary. Obfervation. Werner fuppofes that it is intermediate between clayftone and limeltone, from the refemblance bears to both of thefe lofliis. Ufe. From the alum ftone of Tolfa the famous Roma 11 alum is manufactured. fifteenth
