WorldWide Drilling Resource

Frequently-Used Geological Terms Part 47 Glossary Adapted from the Dictionary of Geological Terms M Medium-Volatile Bituminous Coal - Bituminous coal, character- istically clustered, containing 23-31% volatile matter, analyzed on a dry, mineral-matter-free basis. Megashear - A strike-slip fault with a horizontal displacement exceed- ing the thickness of the crust significantly. Megatectonics - The tectonics of the very large structural features of the earth. Melanocratic - Dark colored; applied to igneous rocks containing more than 60% mafic minerals (minerals high in magnesium and ferric oxides). Melilite - A group of minerals consisting of an isomorphous solid solution series and may contain some iron. It occurs as a com- ponent of certain recent basic volcanic rocks. Mercalli Scale - An arbitrary scale of earth- quake intensity ranging from 1-12. It is named after Giuseppi Mercalli, an Italian geologist who devised the scale in 1902. Mercator Projection - Amap projection in which the equator is represented by a straight line true to scale, the meridians by parallel straight lines perpendicular to the equator, and the parallels by straight lines perpendicular to the meridians and the same length as the equator. There is great distortion of distances, areas, and shapes in the polar regions because any line of constant direction of the sphere is truly represented on the projection by a straight line. The mercator projection is of great value in navigation and is used for hydrographic charts and to plot trajectories of earth satellites in oblique orbits. Mercury - Aheavy, silver-white to tin-white hexagonal mineral. It is the only metal that is liquid at ordinary temperatures. Native mercury is found as minute fluid globules disseminated through cinnabar (the pri- mary ore of mercury), or deposited from the water of certain hot springs. It usually contains small amounts of silver and com- bines with most metals to form alloys. It is highly toxic if breathed or ingested. Image of native mercury sample. Look for more terms next month! 43 WorldWide Drilling Resource ® FEBRUARY 2016