WorldWide Drilling Resource

WorldWide Drilling Resource ® 15 DECEMBER 2014 Frequently-Used Geological Terms Part 35 Glossary Adapted from the Dictionary of Geological Terms L - Continued Landslide - A term for a variety of processes and landforms involving the downslope movement, under gravity, of masses of soil and rock materials. Types include rockfall, mudflow, slump, and many others. Lapidary - The art of cutting gems, or one who cuts and polishes gems or other stones. Lapis Lazuli - A granular crystalline rock composed of lazurite and calcite. It has a rich blue color and is used as a semi- precious stone. Larvikite - A rock with abundant phe- nocrysts of feldspar used as an orna- mental building stone. Lateral Accretion - Horizontal growth of a sedimentary deposit. Lateral Migration - Movement of oil or gas through permeable zones parallel to the stratification. Lateral Secretion - The theory which states the contents of a vein or lode are derived from the adjacent wall rock. Laterite - A highly weathered red sub- soil or material rich in secondary oxides of iron, aluminum, or both, and devoid of bases and primary silicates. It typically develops in a tropical or forested warm climate. Latitude - Angular distance of a point on the earth’s surface north or south meas- ured along a meridian with the equator being latitude 0º. The North Pole would be considered 90º north and the South Pole would be considered 90º south. Latosol - A group of zonal soils charac- terized by deep weathering and abundant hydrous-oxide material. They are devel- oped under forested humid tropical set- tings. Lava - Fluid rock from a volcano or fis- sure, as well as the solidified form. Lava Blister - A small hollow steep- sided swelling raised on the surface of a lava flow by gas bubbles puffing up the viscous crust of the flow. Lava Cascade - A cascade of liquid, incandescent lava formed when a lava river passes over a cliff or over a steep p a r t o f i t s c o u r s e . Lava Cone - A v o l c a n i c cone built of Nearly two thirds of India’s state of Goa is covered by a mantle of laterite. Photo courtesy of goadmg.gov.in Photo of a lava cascade in Hawaii courtesy of usgs.gov lava flows, which were very mobile at the time of eruption, resembling a miniature shield volcano. More terms to come next month!