The Elements of Geology; Adapted to the Use of Schools and Colleges

by Justin R. Loomis

In the neighborhood of volcanoes sulphur is found pure and in a crystalline form. It is a constant ingredient in volcanic rocks, and in several of the most important ores, particularly those of lead, copper and iron. The most abundant sulphate is gypsum, which contains twenty-six per cent, of sulphur. In small quantities it is widely diffused in rocks, and in the waters of the ocean.

Chlorine is found principally as an ingredient of rock-salt, which contains sixty per cent, of it, and of sea-water, which contains one and a half per cent.

Fluorine is found, though very sparingly, in nearly all the unstratified rocks. It forms nearly half of the mineral known as Derbyshire spar.

Of the metals, Iron is the only one that is found abundantly. It enters into the composition of nearly all mineral substances. It is generally combined with oxygen, and occurs less frequently as a carbonate or sulphuret. Of volcanic rocks it forms about twenty per cent. Its ores are sometimes found in the form of dikes or seams, having been injected from below; at other times, in the form of nodules or stratified masses, like other rocks of mechanical origin.

Manganese is likewise extensively diffused, but in very small quantity. The other metals are often met with, but their localities are of very limited extent.

Of the metallic bases of the earths and alkalies, Silicium is the most abundant. It generally occurs in the form of silex, which is an oxide of the metal. There are but few rocks in which it is not found in considerable amount.

Aluminium generally occurs as an oxide, in which form it is alumina. It is the base of the different varieties of clay and clay-slate. It is also a constituent of felspar and mica.

Potassium is an ingredient of felspar and mica, and hence is found in all the primary and in most of the volcanic rocks, as well as in the stratified rocks derived from them.

Sodium is a constituent of a variety of felspar which is somewhat abundant in volcanic rocks. Its principal source is the extensive beds of rock-salt, and the same substance in a state of solution in the waters of the ocean.

Calcium constitutes about forty per cent, of limestone, and is an ingredient in nearly all igneous rocks. This metal, in the state of an oxide, is lime.