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]

earthquake: a shaking or sliding of a portion of the earth's crust, caused by the sudden movement of masses of rock along a fault or by changes in the size and shape of masses of rock far beneath the earth's surface. Earthquakes are often associated with volcanic activity. [AHDOS]

ejecta: matter ejected, as from a volcano. [AHDOS]

eluvial: having to do with or formed by eluviation. [AHDOS]

emerald: a bright-green transparent variety of beryl, whose color is due to traces of chromium. [AHDOS]

emery: a hard, dark granular rock consisting of corundum with various iron minerals. [AHDOS]

emplectite: a mneral consisting of sulfur, bismuth, and copper, occurring in thin prismatic crystals of a grayish or white color and bright metallic luster. [AHDOS]

endogenic: formed within the earth; proceeding from inside the earth. [AHDOS]

endomorph: a mineral enclosed within another mineral. [AHDOS]

Eocene: the second epoch of the Tertiary period, after the Paleocene and before the Oligocene, during which the ancestors of many modern mammals appeared; the rocks formed during this epoch. [AHDOS]

eon: any span of time longer than an era; one billion years. [AHDOS]

epicenter: a point on the earth's surface directly above the focus or true center of an earthquake. [AHDOS]

epoch: one of the divisions of time into which a period is divided. [AHDOS]

era: one of the major divisions of geologic time. An era is usually divided into periods. [AHDOS]

erode: to wear away gradually by erosion. [AHDOS]

erosion: a gradual wearing away by the action of glaciers, running water, waves, or wind.

erosion surface: a surface of land shaped by the action of rain, wind, ice, and other agents of erosion. [AHDOS]

erratic: transported from its original site, as by glacial action. [AHDOS]

erupt: to eject material at the earth's surface, as a volcano or geyser. [AHDOS]

escarpment: a steep slope or descent; a steep face marking the termination of high land or of stratified rocks. [AHDOS]

estuary: a broad mouth of a river into which the tide flows, especially an inlet of the sea at the lower part of a river; formed or deposited in an estuary. [AHDOS]

evaporite: a sedimentary deposit formed as a result of the evaporation of seawater or salne lake water. [AHDOS]

exomorphic: having to do with changes in surrounding rocks by the intrusion of igneous matter. [AHDOS]

exsolution: the process by which a pair of minerals in solid solution separate from one another at certain temperatures. [AHDOS]

fall line: a line that marks the end of layers of hard rock, such as the edge of a plateau or piedmont, and the beginning of a softer rock layer, such as that of a plain. There are many waterfalls and rapids along the fall line. [AHDOS]

fault: a break in the earth's crust, with the mass of rock on one side of the break displaced. [AHDOS]

fault line: a line formed by the interssection of a fault plane with the surface of the earth; the trace of a fault. [AHDOS]

fault plane: the plane along which a faulting occurs. [AHDOS]

feldspar: any of a group of common rock-forming minerals composed of silicate of aluminum, combined with sodium and either potassium or calcium. [AHDOS]

feldspathoid: any of a group of rock-forming minerals chemically similar to the feldspars but containing less silica. [AHDOS]

felsic: consisting of or having to do with a group of light-colored silicate minerals occurring in igneous rocks. [AHDOS]

felsite: an aphanitic volcanic rock consisting chiefly of feldspar and quartz in minute crystals. [AHDOS]

ferrous: of or containig iron, especially divalent iron. [AHDOS]

ferruginous: of or containing iron; like that of iron. [AHDOS]

fiord or fjord: a long, narrow bay of a sea bordered by steep cliffs. [AHDOS]

fissile: (of a rock) that can be split or divided easily along close parallel planes. [ADHOS]

fission-track dating: a method of determining the age of rocks and other geological formations by counting the characteristic tracks left by spontaneous fission of uranium 238 during the lifetime of each sample. The number of tracks is proportional to the age of the sample. [AHDOS]

fissure: a long, narrow opening or crack in a rock; to form a fissure. [AHDOS]

floor: the bed or bottom of the ocean; seabed; a flat surface at the bottom; an underlying stratum on which a seam of coal or other rock lies; a large, level surface. [ADDOS]

flow line: (in igneous rocks) a band of color or an arrangement of crystals that indicates the differential flow of the molten mass before solidification. [AHDOS]

flow structure: the structure in igneous rock produced by the flow of the molten mass before solidification. [AHDOS]

fluorite: a transparent or translucent mineral, composed of calcium and fluorine, that occurs in many colors. It is used for fusing metals, making glass, etc., and is a source of fluorine. [AHDOS]

fluorspar: fluorite. [AHDOS]

fluvial: of, found in, or produced by a river. [AHDOS]

fluviatile: of or resulting from the action of a river. [AHDOS]

fluvioglacial: of or having to do with the combined action of rivers and glaciers. [AHDOS]

flysch: a partly Tertiary, partly Cretaceous formation, consisting chiefly of sandstone, soft marls, and sandy shales, and found in the Alps and other places. [AHDOS]

footwall: the side of rock under a fault, vein, lode, etc. [AHDOS]

fracture: an irregular breaking or cracking of a mineral; a break or crack in rocks due to faulting or folding; to break or crack irregularly. [AHDOS]

fragmental or fragmentary: formed from fragments of older rocks. [AHDOS]

friable: easily crumbled; crumbly. [AHDOS]

fringing reef: a coral reef formed close to the shoreline. [AHDOS]

frostline: the maximum depth to which frost penetrates into the ground in a given locality, as measured during winter. [AHDOS]

fulgurite: partially fused sand in the form of long, slender glass tubes formed by lightning striking unconsolidated sand or soil. [AHDOS]

fumarole: ahole or vent in the earth's crust in a volcanic region, from which steam and hot gases issue. [AHDOS]

fusain: a coal lithotype characterized by black color, silky luster, fibrous structure, and friability. It occurs in patches or strands, and is soft and dusty if not mineralized. [AHDOS]