Glossary of terms
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A-B | C-D | E-F | G-H | I-K | L-N | O-Q | R-T | U-Z | [Sources]

labradorite: a triclinic feldspar that is an essential constituent of basalts and gabbros. [AHDOS]

lag fault: a type of overthrust fault in which the upper part of the stratigraphic section has moved less than the lower part. [AHDOS]

land: the solid part of the earth's surface. [AHDOS]

landslide: a sliding down of a mass of soil or rock on a steep slope. [AHDOS]

langbeinite: an evaporate mineral, a sulfate of potassium and magnesium, that occurs in potassium salt deposits and is mined as a source of potassium sulfate fertilizer. [AHDOS]

lateral moraine: a low ridge-like mass of loose rock pieces carried on, or deposited at, the side of a mountain glacier. [AHDOS]

laterite: a reddish soil rich in iron or aluminum or both, formed under tropical conditions by the decomposition of rock, and commonly found in parts of India, southwestern Asia, and Africa. [AHDOS]

Laurasia: the protocontinent of the Northern Hemisphere, a hypothetical landmass comprising North America, Europe and Asia, which according to the theory of plate techtonics began to break up into the present continents during the Cenozoic era. [AHDOS]

lava: the molten rock flowing from a volcano or fissure in the earth; the rock formed by the cooling of this molten rock.l Some lavas are dense and glassly or crystalline, others are light and porous. [AHDOS]

lava cave: a cave formed by the partial collapse of the roof of a lava tube. [AHDOS]

lava cone: a volcanic cone built entirely or mainly of lava flows. [AHDOS]

lava dome: a dome-shaped volcano built up of many lava flows issued from the central vent of a volcano. [AHDOS]

lava field: a large area of cooled lava. [AHDOS]

lava flow: the flow of lava from a volcano or fissure. [AHDOS]

lava tube: a hollow subterranean channel in a lava flow formed by withdrawal of the lava after solidification of the superficial crust. [AHDOS]

lazulite: a hydrous phosphate of aluminum, magnesium, and iron, often found in azure-blue monoclinic crystals. [AHDOS]

lazurite: a mineral that is the chief component of lapis lazuli; one of a group of minerals chemically similar to feldspar. [AHDOS]

leach: to dissolve out soluble parts from (ashes, rocks, ores, or other matter) by running water or other liquid through slowly; to lose soluble parts as water or other liquid passes through. [AHDOS]

lechatelierite: the glassy form of silica produced by the heat of lightning or meteoric impact. [AHDOS]

lee side: the side of rock, dune, glacier, etc., that is away from the direction in which the wind is blowing. [AHDOS]

lepidolite: a speices of mica containing lithium, commonly occurring in pegmatites as lilac, rose-colored, or grayish-white scaly masses. [AHDOS]

leucite: a white or grayish mineral, a silicate of potassium and aluminum, found in alkalic volcanic rocks. Leucite belongs to a group of minerals that are chemically similar to feldspar. [AHDOS]

levee: a raised bank along a river, occurring naturally as the result of deposits left during successive floods. [AHDOS]

Liassic: the earliest epoch of the European Jurassic period, characterized by clayey rocks with fossils; the rocks of this epoch. [AHDOS]

lignite: a brownish-black coal in which decomposition of vegetable matter has proceeded farther than in peat but not as far as bituminous coal. Lignite usually has the original form of the wood clearly visible. Also called brown coal. [AHDOS]

limestone: a rock consisting mostly of calcite (calcium carbonate), much used for building and in the steel and chemical industries. Limestone yields lime when calcined. Marble is a metamorphosed limestone. [AHDOS]

limonite: any of various minerals consisting of hydrated ferric oxide, found in gossans, lakes and marshes. [AHDOS]

lithic: consisting of stoen or rock. [AHDOS]

lithology: the study of rocks and their composition; the character or composition of a rock or rock formation. [AHDOS]

lithosol: any of a group of shallow soils with no distinct profiles, made up of imperfectly weathered rock fragments. [AHDOS]

lithosphere: the solid portion of the earth as opposed to the atmosphere and the hydrosphere; the rigid outer layer of the earth, comprising the crust and upper mantle. [AHDOS]

lithotype: one of the four microscopically recognizable constituents of bonded coal; vitrain, clarain, durain, or fusain. [AHDOS]

littoral: of, belonging to, or found on or near the shore. [AHDOS]

lodestone: a piece of magnetite that possesses polarity and attracts iron and steel. [AHDOS]

loess: a yellowish-brown marl or loam, usually deposited by the wind. [AHDOS]

lopolith: a centrally sunken body of intrusive igneous rock. [AHDOS]

Lower Carboniferous: the name outside North America for th eMississippian period; the rocks formed in this period. [AHDOS]

lowland: a land that is lower and flatter than the neighboring country. [AHDOS]

macle: a twinned crystal. [AHDOS]

macrofossil: a macroscopic fossil; a plant or animal fossil that is large enough to be seen and examined without a microscope; [AHDOS]

mafic: consisting of or designating any of a group of dark minerals occurring in igneous rocks, composed chiefly of magnesium and iron. [AHDOS]

magma: the molten material beneath the earth's crust from which igneous rock is formed. [AHDOS]

magnesite: natural magnesium carbonate, occurring either in compact, white masses or in crystalline form, used in producing carbon dioxide and steel. [AHDOS]

magnetite: an important iron ore that is strongly attracted by a magnet. Magnetite that possesses polarity is called lodestone. [AHDOS]

manganese spar: rhodonite or rhodochrosite. [AHDOS]

manganite: a hydrated oxide of manganese, occurring in steel-gray or iron-black masses or crystals. [AHDOS]

mantle plume: a large upwelling of molten material from the earth's mantle. [AHDOS]

marble: a metamorphic rock formed by recrystallization of limestone or dolomite, usually white or variegated and capable of taking a high polish. It is widely used as a decorative stone. [AHDOS]

marcasite: a whitish-yellow mineral with a metallic luster, similar in form to pyrite but having a different crystallization and lower specific gravity. [AHDOS]

mascon: a massive concentration of dense material lying below the lunar surface and characterized by a higher-than-average gravity. [AHDOS]

massive: composed of compact material with an irregular form; not macroscopically crystalline; without definite structural divisions. [AHDOS]

medial moraine: the moraine that occurs when the lateral moraines of two glaciers meet and merge. [AHDOS]

megacryst: a large mineral crystal of metamorphic origin in a finer-grained matrix. [AHDOS]

megaseism: a great or sever earthquake. [AHDOS]

melanite: a velvet-black variety of calcium garnet containing titanium. [AHDOS]

meltwater: water formed from melting ice or snow, expecially from a glacier. [AHDOS]

Mercalli scale: a scale for measuring the magnitude of an earthquake, ranging from 1 to 12. [AHDOS]

mesa: an isolated, high plateau with a flat top and steep sides, common in dry regions of the western and southwestern United States. [AHDOS]

Mesozoic: the geological era before the present (Cenozoic) era. It is characterized by the development of mammals, flying reptiles, birds, and flowering plants, and the appearance and death of dinosaurs. It comprises the Triassic, Jurrasic, and Cretaceous periods; the rocks fromed in this era. [AHDOS]

mettalogenetic: producing metals. [AHDOS]

metamorphic: changed in structure by heat, moisture, and pressure. Slate is a metamorphic rock that is formed from shale, a sedimentary rock. [AHDOS]

metasomatism: the process by which the chemical constitution of a rock is changed by the action of fluids. [AHDOS]

meteorite: a meteor that has reached the earth without burning up. Meteorites are of two types --stony and metallic. The later consist mainly of iron, plus substantial amounts of nickel. Iron meteorites survive tghe trip through the atmosphere better than the stony ones. [AHDOS]

mica: any of a group of minerals that can be divided readily into thin, partly transparent, and usually flexible layers. Mica is a hydrous potassium silicate, highly resistant to heat and is used in electric fuses and other electrical equipment. [AHDOS]

microcline: a triclinic potash fledspar silimar to orthoclase, white, yellow, red or green in color. [AHDOS]

microcontinent: an oceanic ridge or plateau thought to have been broken off and separated from a continent during continental drift. [AHDOS]

microearthquake: a small earthquake, of magnitude 2 or less on the Richter scale. [AHDOS]

microfossil: a microscopic fossil, as of foraminifera or a pollen grain. [AHDOS]

micrometeorite: a tiny particle of meteoric dust, so small that it does not burn as it falls to the earth from outer space. [AHDOS]

microseism: a faint, recurrent earth tremor lasting from 1 to about 9 seconds, detectable only with a seismograph. Microseisms are not related to earthquakes, but are due to atmospheric disturbances. [AHDOS]

microtektite: a microscopic variety of tektite found deep in ocean sediments. [AHDOS]

migmatite: a common type of hybrid rock formed of a complex mixture of igneous and metamorphic rocks, characterized by gneissic bands and crosscutting veins. [AHDOS]

miliolite: a fossil foraminifer whose minute shells occur in immene numbers in some strata and are the chief constituent of certain limestones. [AHDOS]

millerite: a nickel sulfide, usually occurring in brassy or bronze crystals or in incrustations. [AHDOS]

mineral: an inorganic substance found in nature, having a uniform or restricted chemical composition and a regular crystalline form; any natural substance obtained by mining or quarrying, such as coal, ore, salt, and stone. Gold, silver, and iron are metallic minerals; quartz, feldspar, and calcite are nonmetallic minerals. [AHDOS]

mineralogy: the science of minerals. [AHDOS]

mineral spring: a spring that yields mineral water. [AHDOS]

mineral water: spring water containing various mineral salts, elements, or gases. The mineral salts or elements may include Epsom salts, calcium, iron, magnesium, boron, fluorine, and others. The gases are usually carbon dioxide and hydrogen sulfide. [AHDOS]

minor planet: asteroid. [AHDOS]

Miocene: the fourth epoch of the Tertiary period of the Cenozoic, after the Ogliocene and before the Pliocene. During the Miocene, grasses developed and grazing mammals fluorished; rocks formed during that epoch. [AHDOS]

Mississippian: the fifth period of the Paleozoic era, after the Devonian and before the Pennsylvanian; Lower Carboniferous (the name used outside of North America); the rocks formed during this period. [AHDOS]

mofette or meffette: an opening or fissure in the earth in a late-stage volcanic area, from which gases, expecially carbon dioxide, emanate; an emanation from such an opening. [AHDOS]

Mohs scale: an empirical scale for classifying minerals on the basis of relative hardness, determined by the ability of harder minerals to scratch softer ones. Values for the Mohs scale are as follows: talc 1; gypsum 2; calcite 3; fluorite 4; apatite 5; orthclase 6; quartz 7; topaz 8; corundum 9; diamond 10. [AHDOS]

mold: an impression or cavity made in earth or rock by the inner or outer surface of a fossil shell or other organic structure. [AHDOS]

molecular fossil: a molecule of organic material extracted from rocks used to study the early development of life on earth. [AHDOS]

molybdenite: a soft, native sulfide of molybdenum that resembles graphite. It is the chief ore of molybdenum. [AHDOS]

monadnock: an isolated hill or mountain of resistant rock standing in an area that is almost level from erosion. [AHDOS]

monazite: a phosphate of cerium and related rare-earth metals, found in small reddish or brownish crystals. [AHDOS]

monoclinal: dipping or sloping in one direction and at the same angle; or or having to do with strata that dip in the same direction. [AHDOS]

monocline: a monoclinal rock formation of fold, such as the oblique portion of a belt of strata at the place where it changes from one horizontal position to another of a different level. [AHDOS]

monticule: a minor cone of a volcano; a little mound or hilltop. [AHDOS]

monzonite: an igneous rock composed of nearly equal amounts of plagioclase and orthclase containing sodium and other minerals, intermediate in composition between syenite and diorite. [AHDOS]

moraine: a mass or ridge of earth, rocks, etc., deposited at the sides or end of a glacier. The material is scraped up by the glacier as it moves along. [AHDOS]

moulin: a nearly vertical shaft or cvityworn in a glacier by surface water falling through a crack in the ice. [AHDOS]

mound: a small or low rounded hill of earth. [AHDOS]

mountain: a very high hill; a natural elevation of the earth's surface rising high above the surrounding level, usually higher than 600 meters. [AHDOS]

mountain range: a row of connected mountains; large group of mountains. [AHDOS]

mountain system: a group of geologically related mountain ranges. [AHDOS]

mudbank: a bank or shoal of mud beside or rising from the bed of a river, lake, or sea. [AHDOS]

mudflat: a stretch of low-lying, muddy land along a shore or island, usually submerged at high tied and left uncovered at low tide. [AHDOS]

mudflow: a flowing mass of fine-grained earth material. [AHDOS]

nacrite: a clay mineral consisting of hydrous silicate of aluminum. It is polymorphous with kaolinite and dickite. [AHDOS]

nanofossil: a very small or microscopic fossil. [AHDOS]

native: found chemically uncombined in nature. Native metals include gold, silver, platinum, copper, iron, lead, mercury, iridium and palladium. [AHDOS]

natural bridge: a rock formation shaped like a bridge and spanning a ravine or valley, especially one made by water working its way slowly through the rock. [AHDOS]

Nebraskan: of or having to do with the first period of glaciation in North America, beginning about 1,200,000 years ago, and lasting about 64,000 years. [AHDOS]

neck: the erosional remnant of a pipelike vent of an extinct volcano, filled with solidified lava. [AHDOS]

Neogene: the later of two periods of the Cenzoic era, comprising the Miocene, Pliocene, Pleistocene, and Recent epochs. The earlier period is the Paleogene; the system of rock strata formed during this period or system. [AHDOS]

neoglacial: of or having to do with neoglaciation. [AHDOS]

neoglaciation: the formation of new glaciers, or readvance of older glaciers, particularly during the so-called Little Ice Age in the northern hemisphere between 1600 and 1850. [AHDOS]

nepheline: a silicate of aluminum, sodium, and sometimes potassium. Nepheline occurs in various volcanic rocks and is chemically related to feldspar. [AHDOS]

nephelinite: a heavy, dark-colored, volcanic rock, essentially a basalt containing nepheline and pyroxene but no feldspar and little or no olivine. [AHDOS]

nephrite: a type of jade, a silicate of calcium and either magnesium or iron, varying in color from white to dark green. [AHDOS]

nickeliferous: containig or yielding nickel. [AHDOS]

nivation: erosion of the ground beneath a snowbank, caused chiefly by alternate freezing and thawing. [AHDOS]

nonconformity: an unconformity in which an erosion surface on plutonic or metamorphic rock has been covered by younger sedimentary or volcanic rock. [AHDOS]

norite: a granular igneous rock solidified below the earth;s surface, containing pyroxene in orthorhombic form and plagioclase containing calcium. Norite is a variety of gabbro, often associated with ore deposits. [AHDOS]

novaculite: a very tough sedimentary rock composed mostly of microcrystalline quartz, used especially for hones and for grinding wheels. [AHDOS]