£24 CLAY""GENUS. ' FIRST S'UB s'PEClfS. Common Alum Slate. - • id: Gemeiner Alauufchiefer.—Werner. bchiflus aluminaris ? Wall. t. 2. p. 32.—Variety of alum flate, Wid. p. 396—Alaunfchiefer, Ejlner, b. 2. f. 651- —Gemeiner alaiinf.hiefer, Emm. b. 1. f. 496. Schifto aluminofo, Nap• p. 264.—Variete de l’argile fchifteufe, Hauy—Le fchifte alumineux, commun, Broch. t. X. 386. External Characters. Its colour is intermediate between greyifh and bliwflr black, which falls ftrongly-into grey. Occurs: maffive, and fometimes in balls' which arc immerfed in the mallive. Internally it is more or lefs glimmering. Fratture pretty perfe&ly ftraight flaty. I’ragments tabular. Retains its colour in the ftreak, but becomes a little firming. Soft. Net