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Pot-ßone. 155 This defcription, is fbr the moft pärt taken from Mr. Karften, who very properly diftinguifhes this foflil from common fteatites. Heated to rednefs, it becomes grey and harder, and at 147 0 forms a grey porous porcelain mafs. yth Species. Pot-Stone. Lapis Ollaris. Verhärteter Talk, or Topfitein of Werner. Colour, light or dark greenilh grey, or green- ifh and reddilh grey, or yellowifti grey, or fpeckled with red, or leek green. Luftre, 2.1.3. Tranfparency, 1 0.2. Fradture, undulatingly foliated, or the folia exceeding thin, and difcovering rugofities; often allo flaty. Fragments, long fplintery, or plated. The foliated prefent fometimes grofs or mi- nute diftindt concretions. Hardnefs, from 4 to 6. brittle. Sp. gr. of that of Como, the moft famons of this fpecies, is 2,8729. According to Sauflure, that of Swifler- land has its fp. gr. 3,023. Some abforb water, the fp. gr. of the potftone of Dauphine, which is of flaty Itrudture before the admiflion of water, is 2,7687; after admiflion 2,8214; of the Swedilh, before the admiflion of water, 2,8531; after admiflion, 2,8629. Feels greafy. This ftone is often confounded with indurated fteatites, which poflibly may have been applied to the fame ufe, but whofe charadters and compofition are very different; it is more difficultly diftin- guilhed from fhiltofe talc, efpecially where the potftone