----------------------------------------------------------------- | | |Oxide|Lime and | |Silica.|Alumina.| of |Magnesia.|Alkalies. | | |iron | | ----------------------------------------------------------------- | % | % | % | % | % Sandstone, grit, | | | | | quartzite, &c. |80-100 | -- | -- | -- | -- Granite, gneiss, | | | | | quartz-porphyry, | | | | | fire-clay, &c. | 70-75 | 13-20 | 2 | 2 | 5-8 | | | | |Less in | | | | |fire-clay. Mica-schist | 65 | 18 | 5 | 3 | 3 Trachyte, syenite | 60 | 17 | 7 | 4-7 | 6-9 Clay-slate | 60 | 18 | 10 | 8 | 3 Diorite | 54 | 17 | 12 | 9 | 3-4 Horneblende-rock | 50 | 18 | 15 | 12 | 3-4 Brick-clay | 50 | 34 | 8 | 6 | -- China-clay | 47 | 39 | -- | -- | -- Basalt, dolerite, &c.| 50 | 15 | 15 | 16 | 3 Serpentine | 44 | -- | -- | 44 | -- Chalk, limestone, | | | | | dolomite, &c. | -- | -- | -- | 45-55 | -- -----------------------------------------------------------------