Chemistry of Minerals

Nearly all rocks are composed of minerals, but fine specimens are rare and tend to occur in what is called fissures and other cavities where the crystals have been unobstructed during their growth.

Many are obtained from the mineral veins. High temperature fluids deposit minerals in cracks and fissures in rocks and many of these veins, often called hydrothermal veins, are worked as sorces of ore. They frequently contain colorful specimens and good crystals, not only of the commercially valuable ore minerals, but also of the accompanying and economically valueless gangue minerals as well.

It is not always necessary to examine or collect from the veins themselves - in many instances, it is dangerous or impossible to do so - for mining activity usually results in dumps of discarded material which, if carefully searched, will often yield good specimens.

Good crystals can often be found lining cavities in rocks of virtually every kind, though particular minerals tend to occur in certain environments. Sometimes wearthered-out cavity linings, called geodes, are lined with well shaped crystals, and many fine crystals of amethyst occur in such associations.

Pegmatites, which crystallize from relatively low temperature, volatile rich magma (fluids), are another source of crystals and rare minerals that frequently grow to large sizes.

Collectors will find some crystals and minerals that are difficult to identify. They are urged to become acquainted with minerals that are displayed in many national and other museums. Time spent in this way will be amply repaid, not only in terms of identification of specimens, but also in becoming more deeply involved in the study of natural history.