WorldWide Drilling Resource

14 JUNE 2019 WorldWide Drilling Resource ® Frequently-Used Geological Terms Part 82 Glossary Adapted from the Dictionary of Geological Terms R Rheid - A substance (below its melting point) which deforms by viscous flow during the time of applied stress at an order of magnitude at east three times that of elastic deformation under similar conditions. Rheology - Study of the deformation and flow of matter. Rhizoconcretion - A small cylindrical or conical structure in a sedimentary rock, usually branching or forked, resembling a root of a tree. It may consist of material such as caliche or chert. Rhodochrosite - A rose red or pink to gray rhombohedral mineral of the calcite group. It is isomorphous with calcite and siderite, and commonly contains some calcium and iron. It is a minor ore of manganese. Rhodolite - A pink, rose, or violet garnet, intermediate in chemical composition between pyrope and almandine. It has a light color and a high degree of trans- parency, and is used primarily as a gemstone. Rhombic Dodecahedron - A 12-sided crystal. Rhombohedron - A crystal form in the hexagonal system bounded by six faces. Rhomb Spar - Mineral dolomite in rhombohedral crystals. Rhyolite - A group of extrusive igneous rocks, typi- cally porphyritic and commonly exhibiting flow tex- ture, with phenocrysts of quartz and alkali feldspar in a glassy, to cryptocrystalline groundmass. Also refers to any rock in that group; the extrusive equivalent of granite. Rib - A layer or dike of rock forming a small ridge on a steep mountainside. Also used to describe an elongated pillar left in a mine for support. Could also be said of a radial or transverse fold on a fossil shell, such as a raised ridge on the coiled conch of an ammonoid or nautiloid. Ribbon Injection - A tonguelike igneous intrusion along the cleavage planes of a foliated rock. Ribbon Rock - A rock characterized by a succession of thin layers of differing composition or color, such as a vein with narrow quartz bands separated by stripes of altered wall rock. Look for more terms next month! In 2002, rhodochrosite was declared Colorado’s official state mineral. MIN