434 IIYDROTXS SILICATES. a b C d 39'98 40-38 37-83 38-15 8'28 10-79 12-95 11-31 17-05 13-52 9’93 10-48 00 00 8-68 7’49 7'78 4'45 8'35 0-54 0-14 0-43 0-04 0-94 0-78 0-01 0-01 0’70 0-64 18-25 10-98 23-00 24-09 1-89 2'32 0-98 2-19 Silica . . . Alumina . . Protoxide of iron Lime . . . Magnesia . . Potash . . . Soda . . . Water . . . Insoluble . . Is found massive and disseminated as an ingredient of the volcanic tufa in the neighbourhood of Palagonia in the Val di Noto in Sicily, and in Iceland, especially at Seljadlr half way between Reykiavik and Thingvellir. 271. GROPPITE.—Groppit; Svanberg, Hausmann. Has one distinct cleavage, and two cleavages less distinct. Practure splintery. In thin fragments semi-transparent. Rose- red... brown-red. Streak light. Brittle, 11=2-5. o = 2 73. In the matrass yields water. Before the blowpipe becomes white and melts on the edges. Easily soluble with effervescence in borax. Analyses by Svanberg:— Silica 45-oi Alumina 22-65 Red oxide of iron . . . 3-00 Magnesia 1228 Lime 4-55 Potash 5-23 Soda 0*22 Water 7-11 Undecomposed mineral . 0'13 Is found in crystalline clenvable masses in the limestone quarry of Gropptrop in the parish of Wingaker in Soderman- land in Sweden. 272. CHLOROPAL.—Chloropal; Mohs, Hausmann, Hni- dinger. Practure conchoidal...earthy. Opaque...translucent 011 the edges. Lustre vitreous, dull. Brittle. 11 = 3 0...4 0. a = 2'0. Becomes black and magnetic before tho blowpipe, but does not melt. With fluxes yields the reaction of iron.