|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 | --
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Silica itself, and the silicates of alumina, of lime, and of magnesia,
are practically infusible; the silicates of soda, of potash, and of iron
are easily fusible if the base (soda, potash, or oxide of iron) be
present in sufficient quantity, and if, in the case of the iron, it is
present mainly as lower oxide (ferrous silicate).
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