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Inland Lapidary - Gem glossary
Category: General technical and industrial > Gems and Geology
Date & country: 27/10/2013, USA
Words: 1119

covalent bond
The combination of two or more atoms by sharing electrons so as to achieve chemical stability under the octet rule. Atoms that form covalent bonds generally have outer energy levels containing three, four, or five electrons. Covalent bonds are generally stronger than other bonds.

Aggregate composed of flaky or tabular crystals that seem adjoined from a base; with grooves between long, slender, arc-like crystals.

A hole that was created in the earth or celestial body from the impact of a meteor.

The segment of the Earth's continents that have remained tectonically stable and relatively earthquake-free for a vast period of time. The craton is composed of the continental shield and the surrounding continental platform.

Condition in opal that causes it to form small, internal cracks, and in some severe cases will eventually disintegrate the opal.

The slowest form of mass movement, measured in millimeters or centimeters per year and occurring on virtually all slopes. cross bed A bed made up of particles dropped from a moving current, as of wind or water, and marked by a downward slope that indicates the direction of the current that deposited them.

1. The outermost layer of the Earth, consisting of relatively low-density rocks. See also core and mantle. 2. A disorganized, crusty, mineral coating that can be thin or thick. 3. Type of aggregate.

Aggregate of a crust coating on a rock or mineral.

Composed of tiny, microscopic crystals.

A mineral in which the systematic internal arrangement of atoms is outwardly reflected as a latticework of repeated three-dimensional units that form a geometric solid with a surface consisting of symmetrical planes.

crystal angle
The sum of the angles on a crystal edge that are characteristic to a crystal set.

crystal face
The side of a crystal. The number of faces varies with the crystal's structure.

crystal form
The shape and habit of a particular crystal.

crystal habit
The habitual form that a mineral forms it crystallizes.

crystal lattice
The arrangement of atoms in a crystal, giving each crystal its distinct shape. See also crystal structure.

crystal structure
1. The geometric pattern created by the systematic internal arrangement of atoms in a mineral. 2. The systematic internal arrangement of atoms in a mineral.

crystal system
The primary method of classification of crystals. The Crystal system classifies crystals in six groups. They are: Isometric, Tetragonal, Hexagonal (which includes Trigonal), Orthorhombic, Monoclinic, and Triclinic. The crystal class, which classifies crystals into 32 crystal types, is a more precise classification of crystal groupings.

1) Having a crystal structure. 2) Composed of visible crystals.

The forming of crystals or to assume a crystal shape.

To form a crystal shape, or to have crystals in a particular group.

Containing a crystal form. May also be referred to molten rock that solidifies and forms a crystal shape.

The science and study of crystal structure. Person who studies crystallography is a crystallographer.

Abbreviation for carat

Six sided polyhedron; all sides are equi-dimensional and bisect at 90�. Minerals shaped as cubes belong to the isometric system.


cubic crystal system
Synonym of isometric system.

1. n A description of the type of facet. 2. v Meaning faceted.

cyclosilicates group
Group of silicate minerals that have their tetrahedrons linked into rings. Each silicon atom is bound by two oxygen atoms that are part of another tetrahedron. Each ring consists of three, four, or six linked tetrahedrons.

daughter isotope
An isotope that forms from the radioactive decay of a parent isotope. A daughter isotope may or may not be of the same element as its parent. If the daughter isotope is radioactive, it will eventually become the parent isotope of a new daughter isotope. The last daughter isotope to form from this process will be stable and nonradioactive.

debris flow
1. The rapid, downward mass movement of particles coarser than sand, often including boulders one meter or more in diameter, at a rate ranging from 2 to 40 kilometers per hour. Debris flows occur along fairly steep slopes. 2. The material that descends in such a flow. deflation The process by which wind erodes bedrock by picking up and transporting...

The molecular breakdown of certain minerals which cause a mineral to disintegrate.

An explosive shattering of minerals, usually through tube tests or blowpipe tests.

The process by which a stream's gradient becomes less steep, due to the erosion of sediment from the stream bed. Such erosion generally follows a sharp reduction in the amount of sediment entering the stream.

The removal of water from a substance. Many minerals naturally lose water in their structure at normal conditions, and the mineral transforms into another mineral.

An alluvial fan having its apex at the mouth of a stream.

Aggregate composed of skeletal or tree-like formations. May be a single entity, or a formation that forms from mineral-rich solutions that deposit the mineral in rock and form a tree or plant structure embedded in rock. There sometimes is a distinction noted between the two aggregates; in some guides the former aggregate (single entity) is known as...

A method of numerical dating that uses the number of tree rings found in a cross section of a tree trunk or branch to determine the age of the tree.

An accumulation of certain minerals within a rock formation.

A region with an average annual rainfall of 10 inches or less and sparse vegetation, typically having thin, dry, and crumbly soil. A desert has an aridity index greater than 4.0.

desert pavement
A closely packed layer of rock fragments concentrated in a layer along the Earth's surface by the deflation of finer particles.

desert varnish
A thin, shiny red-brown or black layer, principally composed of iron manganese oxides, that coats the surfaces of many exposed desert rocks.

The process through which a desert takes over a formerly non-desert area. When a region begins to undergo desertification, the new conditions typically include a significantly lowered water table, a reduced supply of surface water, increased salinity in natural waters and soils, progressive destruction of native vegetation, and an accelerated rate ...

detrital sediment
Sediment that is composed of transported solid fragments of preexisting igneous, sedimentary, or metamorphic rocks.

Minerals or rock fragments that eroded and end up in a different region from natural causes, such as downstream currents.

The set of processes that cause physical and chemical changes in sediment after it has been deposited and buried under another layer of sediment. Diagenesis may culminate in lithification.

Repelled by magnetic fields. Diamagnetism is the property which causes a mineral to be repelled from magnetic fields.

The quality of of a substance to be seen through. In regard to minerals, it is variable with transparency.

Able to be seen through, being either transparent or translucent.

The bending of light when it enters from one medium into another. For example, light bends as it travels from air into another substance, such as water. Diffraction also occurs when light enters from the air into a mineral, and the amount of diffraction varies among minerals.

A discordant pluton that is substantially wider than it is thick. Dikes are often steeply inclined or nearly vertical. See also sill. dilatancy The expansion of a rock's volume caused by stress and deformation.

Any of a group of dark, phaneritic, intrusive rocks that are the plutonic equivalents of andesite.

The angle formed by the inclined plane of a geological structure and the horizontal plane of the Earth's surface.

dip-slip fault
A fault in which two sections of rock have moved apart vertically, parallel to the dip of the fault plane.

In form with a plane dividing a crystal into two pyramids base to base. Synonym of bipyramid.

directed pressure
Force exerted on a rock along one plane, flattening the rock in that plane and lengthening it in the perpendicular plane.

disappearing stream
A surface stream that drains rapidly and completely into a sinkhole.

Synonym of phyllosilicates.

displaced terrane
A fault-bounded body of rock - sometimes thousands of square kilometers in area - that originated elsewhere geographically and has then moved, perhaps long distances, by plate motion.

A form of chemical weathering in which water molecules, sometimes in combination with acid or another compound in the environment, attract and remove oppositely charged ions or ion groups from a mineral or rock.

dissolved load
A body of sediment carried by a stream in the form of ions that have dissolved in the water.

One of a network of small streams carrying water and sediment from a trunk stream into an ocean.

The process by which two lithospheric plates separated by rifting move farther apart, with soft mantle rock rising between them and forming new oceanic lithosphere. See also convergence.

Changing over from a natural glass to a mineral with a crystalline structure. To devitrify is the process of a natural glass to lose its glassy nature and crystallize.

Twelve sided polyhedron; all sides are equidimensional and either rhombic or pentagonal. If the dodecahedron is composed of rhombs, it is known as a rhombic dodecahedron, or simply as a dodecahedron. If it is composed of pentagons, it is known as a pentagonal dodecahedron or pyritohedron. Minerals shaped as dodecahedrons belong to the isometric sys...

Flat, spherical disc of radiating crystals. Also a variety of Pyrite / Marcasite.

A sedimentary rock composed primarily of dolomite, a mineral made up of calcium, magnesium, carbon, and oxygen. Dolostone is thought to form when magnesium ions replace some of the calcium ions in limestone, to which dolostone is similar in both appearance and chemical structure.

A round or oval bulge on the Earth's surface, containing the oldest section of rock in its raised, central part. See also basin. drainage basin The area from which water flows into a stream. Also called a watershed.

double refraction
Phenomenon exhibited on all non-opaque minerals except for amorphous ones and ones that crystallize in the isometric system. A light ray enters the crystal and splits up into two separate rays, making anything observed through the crystal appear as double. The double refraction on most minerals is so weak that it cannot be observed without special ...

One of the many gem fakes in which a thin, flat section of a real gem is pasted atop a thick base of glass or rock crystal.

doubly terminated
Exhibiting a pinched crystal figure on both bases.

drainage divide
An area of raised, dry land separating two adjacent drainage basins.

drainage pattern
The arrangement in which a stream erodes the channels of its network of tributaries.

A long, spoon-shaped hill that develops when pressure from an overriding glacier reshapes a moraine. Drumlins range in height from 5 to 50 meters and in length from 400 to 2000 meters. They slope down in the direction of the ice flow.

Cavity in a mineral or rock filled with protruding crystals. The hole is either completely filled with crystals or just partially.

Aggregate composed of prismatic crystals protruding from a cavity or wall.

dry lake
Saline lake that evaporated or was drained. Dry lakes leave many evaporite minerals, including salts, borates, and nitrates.

dry lake deposit
Deposit containing an accumulation of evaporite minerals from the evaporation or drainage of a saline lake. As the water gets exhausted, the minerals it is rich in remain, increasing in content, and eventually all that is left is accumulation of the mineral that was once present in the water.

Capable of being stretched into a thin wire. A form of tenacity. Ductility is the capability of being able to stretched into a thin wire.

dull luster
The luster of minerals with very poor optical properties.

Area where left over material is placed after being extracted from a mine.

A usually asymmetrical mound or ridge of sand that has been transported and deposited by wind. Dunes form in both arid and humid climates.

Very thin coating of one mineral on another mineral; a very thin sprinkling.

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 m...

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

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.

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.

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 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.

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.

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

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 r...

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 ...