Silica. One of the pure earths. Etym., silex, flint, because found in that mineral.
Silicate. A chemical compound of silica and another substance, such as silicate of iron. Consult elementary works on chemistry.
Siliceous. Of or belonging to the earth of flint. Etym., silex, which see. A siliceous rock is one mainly composed of silex.
Silicified. Any substance that is petrified or mineralized by siliceous earth.
Silt. The more comminuted sand, clay, and earth, which is transported by running water. It is often accumulated by currents in banks. Thus the mouth of a river is silted up when its entrance into the sea is impeded by such accumulation of loose materials.
Simple Mineral. Individual mineral substances, as distinguished from rocks, which last are usually an aggregation of simple minerals. They are not simple in regard to their nature; for when subjected to chemical analysis, they are found to consist of a variety of different substances. Pyrites is a simple mineral in the sense we use the term, but it is a chemical compound of sulphur and iron.
Sinter, Calcareous or Siliceous. A German name for a rock precipitated from mineral waters. Etym., sintern, to drop.
Slate. See "Cleavage" and "Schist."
Solfatara. A volcanic vent from which sulphur, sulphureous, watery, and acid vapors and gases are emitted.
Sporules. The reproductory corpuscula (minute bodies) of cryptogamic plants. Etym., σπορα, spora, a seed.