WorldWide Drilling Resource

Frequently-Used Geological Terms Part 46 Glossary Adapted from the Dictionary of Geological Terms M Marcasite - A common pale yellow or gray orthorhombic mineral, FeS 2 , dimor- phous with pyrite. It is common as nodules and concretions in sedimentary rocks. Marginal Fissure - A fracture, bordering an igneous intrusion, which has be- come filled with magma. Marlstone - 1. A hardened rock of about the same composition as marl, i.e. an earthy or impure clay-containing limestone. 2. A term originally applied to slightly magnesian calcareous mudstones or muddy limestones in the Green River Formation of the Uinta Basin, Utah, but later applied to associated rocks with a variety of lithologic characters. Abandonment of the term as used in the Uinta Basin has been recommended. Massif - 1. A massive topographic and structural feature, especially in an orogenic belt, commonly formed of rocks more rigid than those of its surroundings. These rocks may be protruding bodies of basement rocks, consolidated during earlier oroge- nies, or younger plutonic bodies. 2. A mountainous mass or group of connected heights, whether isolated or forming a part of a larger mountain system. Mass Movement - Uni t downslope movement of a portion of the land surface, as in creep, landslide, or slip. Matr ix - 1. The groundmass of an igneous rock. 2. The finer-grained material enclosing larger grains in a sediment or sedimentary rock. 3. The rock or sediment in which a fossil is embedded. 4. A gem- stone cut from a mineral and the surround- ing rock material. 5. A local term for the phosphate-bearing gravel in the land- pebble deposits of Florida. Medical Geology - The application of geology to medical and health problems, involving subjects such as the occurrence of toxic elements in unusual quantities in parts of the earth’s crust, the distribution of trace elements as related to nutrition, or the geographic patterns of disease. Mediterranean Suite - A major group of igneous rocks, characterized by high potassium content. This suite was also named due to the predominance of potas- sium-rich lavas around the Mediterranean Sea. Image of a landslide area, also known as a mass movement. Photo by Moralist. Look for more terms next month! 47 WorldWide Drilling Resource ® JANUARY 2016