Glossary of Rock and Mineral Terms - E

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

earthquake

A movement within the Earth's crust or mantle, caused by the sudden rupture or repositioning of underground rocks as they release stress.

earth science

Type of geological science dealing with the physical aspects of the earth, such as its formation, structure, and phenomenons, which include the subjects of rocks and minerals.

earth systems

The Earth is made up of four basic systems: the lithosphere (the rocks of the earth); the hydrosphere (the waters of the Earth); the atmosphere (the gases that surround the Earth); and, the biosphere (the life on Earth). These systems interact to produce most of the geological processes that occur on Earth. An event involving one of these systems may affect some or all of the others.

earthy fracture

Minerals that crumble like loose sandstone when exposed to stress are said be earthy. This term may also be used to describe this crumbling property as a type of fracture.

earthy luster

Luster describing minerals that are microcrystalline or amorphous and have very poor reflective surfaces.

ebb tide

A tide that lowers the water surface of an ocean and moves the shoreline farther seaward.

echo-sounding sonar

The mapping of ocean topography based on the time required for sound waves to reach the sea floor and return to the research ship that emits them.

effervescence

A chemical reaction where bubbles of gas escape a from a liquid, which is caused by two incompatible substances. Carbonate minerals effervesce if they come into contact with hydrochloric acid.

efflorescence

The phenomenon of certain minerals that when exposed to air, lose water from their chemical structure, and develop a white powder on the crystal faces.

elastic

The tenacity of certain minerals that when put under stress will bend, and will return to their original positions when the stress is released. This term is sometimes referred to as "flexible and elastic". The difference between flexible and elastic minerals is that flexible minerals will not return to their original positions after stress is released, but will develop a new position, whereas elastic minerals will return back to their original position.

elastic deformation

A temporary stress-induced change in the shape or volume of a rock, after which the rock returns to its original shape and volume.

elastic limit

See yield point.

electromagnetic radiation

Energy waves produced by the motion of an electric charge.

electrometallurgy

The separation of metals from ore or from alloys through an electrical process, or the forming of alloys and purification of metals through an electrical process.

electron

A negatively charged particle that orbits rapidly around the nucleus of an atom. See also proton.

element

 The classification of atoms. The different atoms are grouped as elements, which distinguishable properties are specified for each one. An element can also refers to a substance whose structure is made up of only a single type of atom. A form of matter that cannot be broken down into a chemically simpler form by heating, cooling, or chemical reactions. There are 115 known elements, 92 of them natural and 23 man-made. Elements are represented by one- or two-letter abbreviations.  The periodical table of the elements is a layout of all the elements.

elongated

Describing a crystal with a lengthened side, meaning that one side is far longer than the other sides which are about equal.

embedded crystal

Crystal that is implanted in rock and can only be extracted if part of the rock is removed.

empirical formula

Chemical formula that has been reduced by means of division. For example, (Si₃O₁₂) can be reduced to (SiO₄) by using the lowest common divisor, which is three. Three divided by three is one {so the second formula contains one silicon (Si) molecule}, and twelve divided by three is four {so the second formula contains four oxygen (O) molecules}. See The Chemical Properties of Minerals for more information.

enaniotropic

Describing a mineral that does not have a consistent crystal structure, meaning that it can transform back and forth into its paramorph when conditions are suitable. Monotropic minerals cannot transform back and forth into their paramorphs. Once they change, they cannot change back without the crystal structure being destroyed.

encrust

To form a coating over.

encrustation

A crusty coating.

energy level

The path of a given electron's orbit around a nucleus, marked by a constant distance from the nucleus.

engrave

To carve letters or an image out of a gemstone.

environment

Area or region conducive for the development of a mineral. Certain minerals only develop in certain environments.

epicenter

The point on the Earth's surface that is located directly above the focus of an earthquake.

epitaxy

The growth of a crystal of one mineral on or around a crystal of another mineral.

epithermal vein

Vein formed at shallow depths from unstable hot solutions.

epsom salts

Salt made of magnesium sulfate (MgSO₄ ·7H₂O) used for stomach medications. Epsom salt is extracted from the mineral Epsomite.

equant

Synonym of equidimensional

equidimensional

Equal in length, width, height, and angles.

equilibrium line

The point in a glacier where overall gain in volume equals overall loss, so that the net volume remains stable. The equilibrium line marks the border between the zone of accumulation and the zone of ablation.

eroded

Having gone through the process of erosion.

erosion

The process by which particles of rock and soil are loosened, as by weathering, and then transported elsewhere, as by wind, water, ice, or gravity.

esker

A ridge of sediment that forms under a glacier's zone of ablation, made up of sand and gravel deposited by meltwater. An esker may be less than 100 meters or more than 500 kilometers long, and may be anywhere from 3 to over 300 meters high.

evaporate

Going through the process of evaporation.

evaporation

The process in which water and moisture rises up to the air and forms vapor.

evaporite

An inorganic chemical sediment that precipitates when the salty water in which it had dissolved evaporates.

even fracture

Mineral fracture forming a smooth, flat surface.

extract

To separate a valuable constituent from its ore.

extraterrestrial

Originating off of the earth. Meteorites are extraterrestrial.

extrusive rock

An igneous rock formed from lava that has flowed out onto the Earth's surface, characterized by rapid solidification and grains that are so small as to be barely visible to the naked eye.