silica

Silica is an invariable constituent of the ash, but in most plants occurs but in small quantity.

Quartz consists of pure silica, and when in large masses is one of the most indestructible rocks.

Silica and the alkalies occur generally, though not invariably, in all three.

In general, sand consists of finely broken crystals of silica or quartz.

Many natural waters present us with silica in a dissolved state, although it is not soluble in pure water.