E

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.

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.

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.

Effervescent

Describing a mineral that effervesces in acid.

Effloresce

To lose water and develop a white powered. (See efflorescence)

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. (i.e. Kernite)

Efflorescent

Describing a mineral that effloresces.

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.

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. See also metallurgy.

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. For example, the mineral Copper, which is made up of 100% the element copper (and no other substances), is known as an element. The periodical table of the elements is a layout of all the elements.

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.

Encrustation

A crusty coating.

Encrusting

Forming a crust.

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.

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.

Erosion

Process where rock is worn away from natural procedures, such as water and wind.

Even (fracture)

Mineral fracture forming a smooth, flat surface. (See Fracture in mineral properties for more information.)

Extraterrestrial

Originating off of the earth. Meteorites are extraterrestrial.