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Prehnite, 27 5 The cryftallized forms either low, fmall, compref- fed, flat, quadrangularprifrns, or tables; and fome with truncated angles, and heaped together, or in groups. The principal fradture is foliated, feldom ftri- ated; the crofs fra&ure uneven, and fine grained. Its hardnefs from 9 to 10. Brittle. Its fp. gr. 2,94.2 3. Expofed to the blovvpipe, it fwe.lls and foams when heated to rednefs {tili rnore than zeolites do, and melts into a brown enamel, fmooth on the outfide, but fptingy and porous underneath. Of the ufual fluxes borax is the mofl: effec- tive; with alkalis it forms only an enamel, but microcoftnic falt forces it into an opal^fcent glafs. By the analyfis of Mr. Klaproth, it contains 0,4383 lilex, 0,3033 argill, 0,1833 calx, 0,0566 iron, and 0,0183 of waterand air. By that of Mr. Haflfenfratz, 0,50 filex, 0,204 argill, 0,233 ca ' x > °>°49 * ron > <>>009 water, and 0,003 niagnefia. This ftone was firft found near the Cape of Good Hope by Capt. Prehn, hence Mr. Werner calls it prehnite. Lately, it has been difcovercd near Dumbarton, in Scotland, by that accurate obferver Mr. Grotfche. It has alfo been found in Dauphine. In luftre, texture, and intumefcence, it refern- bles zeolites, but* ciiffers in hardnefs, fpecific gra- vity, colour, relation to fiures, and alfo in con- ftitution, for it contains iron; neither does it gelatinate with acids as zeolites do. On the other hand, it differs from lhorls, by its fradture, intu- niefcence when heated, greatcr fufibility, and rhe T 2 porofity