Geology

Geology is the study of the form, structure and developmental history of the earth and its contained rocks and minerals. The science of geology is into seven independent fields of study, one of which is mineralogy. Mineralogy is the study of the mineral materials of which ores and rocks are composed with emphasis on the properties, identification, origin and classification of minerals. The properties of minerals, according to which they are identified and classified, are studied under the convenient subdivisions of chemical mineralogy, physical mineralogy, and crystallography. The study of the properties and classification of individual minerals, their localities and modes of occurrence and their uses are studied under descriptive mineralogy. The identification of minerals according to their chemical, physical and crystallographic properties is called determinative mineralogy.

The basic source of most metallic ores is molten rock material or magma. The magma containing metals in solution may intrude itself into overlying rocks. During solidification of the magma into solid rock, the contained metal compounds are expelled in the forms of vapors and gases or as liquid solutions. These hot solutions consisting largely of water may travel along fissures in the rock, and as they cool their metallic content is deposited in the fissures to form veins of gold, silver, copper, or other ores.

In general the geological problems presented by the mining or quarrying of nonmetallic mineral materials are less complex than the geology of metallic ores. Clays and diatomaceous earths are sedimentary in origin and are usually discovered in surface deposits. In prospecting for gems, geological knowledge is essential because gem materials are often associated with specific rocks such as the "blue ground" of South Africa that serves as the matrix for diamonds. Many gems are discovered in placer deposits and the prospector must be acquainted with the geological associations of the stones in order to discover the primary deposit.