far infrared . Pertaining to the longer wavelengths of the infrared region, from 15 μm to 1 mm. The atmosphere transmits very little radiation at these wavelengths, so terrestrial use of this spectral band is severely limited. Cf: reflected infrared.

extinct radionuclide . A radionuclide that was present when a rock or meteorite was formed, but whose half-life is far smaller than the intervening period, with the result that no measurable amount of this nuclide is still present. Its former presence is indicated by an excess in the abundance of the daughter isotope. Cf: isotopic anomaly.

mining geology . The study of the geologic aspects of mineral deposits, with particular regard to problems associated with mining. Cf: mining; mining engineering.

diatomite (di-at'-o-mite). A light-colored soft friable siliceous sedimentary rock, consisting chiefly of opaline frustules of the diatom, typically white, but also pale yellow, gray, or tan. Its low density enables it to float on water. Some deposits are of lake origin but the largest are marine. Owing to its high surface area, high absorptive capacity, and relative chemical stability, diatomite has a number of uses, esp. as a filter aid and as an extender in paint, rubber, and plastics. The term is generally reserved for deposits of actual or potential commercial value. Syn: diatomaceous earth; kieselguhr. Obsolete syn: tripoli-powder. See also: tripoli; tripolite.