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

Consisting of hydrocarbons (such as coal) and materials formed from them.

bituminous coal
A shiny black coal that develops from deeply buried lignite through heat and pressure, and that has a carbon content of 80% to 93%, which makes it a more efficient heating fuel than lignite.

blowpipe test
Complex, scientific test which is conducted to identify a mineral. A mineral fragment is placed in a cavity on a charcoal block, and a horizontal flame is sent towards the fragment on the charcoal using a blowpipe. Depending on the mineral, a different reaction takes place. Certain metals have a characteristic color when flamed, and if the mineral ...

body wave
A type of seismic wave that transmits energy from an earthquake's focus through the Earth's interior in all directions. See also surface wave.

boiling point
The temperature that it takes a substance to start boiling after being in a liquid state.

To combine, by means of chemical reaction, with another atom to form a compound. When an atom bonds with another, it either loses, gains, or shares electrons with the other atom. The link between atoms to form a secure molecule.

Group of minerals that are compounds of one or more metallic elements combined with the borate radical (B2O3). This group forms two sub-groups, the Hydrous borates and the Anhydrous borates.

Industrially used chemical which is an anhydrous form of sodium borate (Na2B4O7) used in the manufacture of glass and ceramics. It is interesting to note that there is a mineral Borax (Na2B4O7 � 10H2&l...

Aggregate resembling a cluster of grapes. Also known as globular. Rounded agglomerations of botryoidal aggregates are smaller than reniform agglomerations and considerably smaller than mammilary agglomerations.

Synthetic gems created from molten liquids placed in tear shaped molds to crystallize, leaving them with a tear-like form. Mostly applied to synthetic Rubies and Sapphires.

Bowen's reaction series
The sequence of igneous rocks formed from a mafic magma, assuming mineral crystals that have already formed continue to react with the liquid magma and so evolve into new minerals, thereby creating the next rock in the sequence.

braided stream
A network of converging and diverging streams separated from each other by narrow strips of sand and gravel.

Man-made alloy of copper and zinc. In the olden times, any alloy of copper was known as brass. Most brass of the olden days was an alloy of copper and tin. See also bronze.

A wall built seaward of a coast to intercept incoming waves and so protect a harbor or shore. Breakwaters are typically built parallel to the coast.

A clastic rock composed of particles more than 2 millimeters in diameter and marked by the angularity of its component grains and rock fragments.

breeder reactor
A nuclear reactor that manufactures more fissionable isotopes than it consumes. Breeder reactors use the widely available, non-fissionable uranium isotope U-238, together with small amounts of fissionable U-235, to produce a fissionable isotope of plutonium, Pu-239.

1. Referring to cut: A type of cut used for certain gemstones. 2. Referring to luster: Synonym of adamantine.

Form of tenacity which describes a mineral that gets hammered and results in a fine powder or small crumbs. Minerals that are not brittle are referred as Nonbrittle minerals. Brittle minerals leave a fine powder if scratched, which is the way to test a mineral to see if it is brittle

brittle failure
Rupture of rock, a type of permanent strain caused by relatively low stress.

Gem or stone without facets that is highly polished and has smooth, rounded edges. (See our How To Cab online guide)

Containing the compound calcium carbonate.

Containing calcium.

calcite (group)
Group of minerals belonging to the carbonate group that are isomorphous with one another and have the same properties, such as that they all: 1. Crystallize in the trigonal sect of the hexagonal system, and most commonly form rhombohedrons and scalenohedrons. 2. Have perfect rhombohedral cleavage 3. Exhibit a very strong double refraction in ...

A vast depression at the top of a volcanic cone, formed when an eruption substantially empties the reservoir of magma beneath the cone's summit. Eventually the summit collapses inward, creating a caldera. A caldera may be more than 15 kilometers in diameter and more than 1000 meters deep.

A white soil horizon consisting of calcium carbonate, typical of arid and semi-arid areas. Brief heavy rains dissolve calcium carbonate in the upper layers of soil and transport it downward; the rainwater then evaporates rapidly, leaving the calcium carbonate to form a new, solid layer of soil.

Gem with a design or figure carved out of the stone, and raised above the background layer

The ability of a given stream to carry sediment, measured as the maximum quantity it can transport past a given point on the channel bank in a given amount of time. See also competence.

Aggregate composed of tiny, thin, straight, long crystal strands; hair like.

capillary fringe
The lowest part of the zone of aeration, marked by the rising of water from the water table due to the attraction of the water molecules to mineral surfaces and other molecules, and to pressure from the zone of saturation below.

Weight measurement used in reference to gemstones in regard to their evaluation. A carat is .2 grams (or 200 milligrams), and this weight is used worldwide, even in the U.S. where the metric system isn't used. A point is the weight used only in reference to very small, precious gemstones, and represents 1/100th of a carat. The abbreviation for cara...

carbon-14 dating
A form of isotope dating that relies on the 5730-year half-life of radioactive carbon-14, which decays into nitrogen-14, to determine the age of rocks in which carbon-14 is present. Carbon-14 dating is used for rocks from 100 to 100,000 years old.

One of several minerals containing one central carbon atom with strong covalent bonds to three oxygen atoms and typically having ionic bonds to one or more positive ions.

carbonates (group)
Group of minerals that contain one or more metallic elements plus the carbonate radical (CO3). Most are lightly colored and transparent when pure. All carbonates are soft, brittle, and effervesce when exposed to warm hydrochloric acid. The carbonates are divided into Calcite Group and Aragonite Group. The Nitrates and Borates are sometimes co...

carlsbad twin
Form of penetration twinning where two Orthoclase crystals form interpenetrating twins as depicted in the figure below.

Ornamental figure, such as a stone lion, carved out of a rock or mineral. A piece of stone formed this way is described as carved.

The hypothesis that a series of immense, brief, worldwide upheavals changed the Earth's crust greatly and can account for the development of mountains, valleys, and other features of the Earth. See also uniformitarianism.

Neutral atom that loses an electron and becomes positively charged.

cave (cavern)
A naturally formed opening beneath the surface of the Earth, generally formed by dissolution of carbonate bedrock. Caves may also form by erosion of coastal bedrock, partial melting of glaciers, or solidification of lava into hollow tubes.

Hollow area in rock that develops because of some form of stress. Many cavities are lined with crystals. See also vug.

The diagenetic process by which sediment grains are bound together by precipitated minerals originally dissolved during the chemical weathering of preexisting rocks.

cementation zone
Underground area where certain elements are concentrated and can combine to form new, or primary, minerals.

Cenozoic Era
The latest era of the Phanerozoic Eon, following the Mesozoic Era and continuing to the present time, and marked by the presence of a wide variety of mammals, including the first hominids.

center of symmetry
Central area on a polyhedron where all the planes of symmetry intersect.

Phenomenon of certain cat's eye minerals which causes it to exhibit a concentrated narrow band of reflected light across the center of the mineral. Chatoyancy is usually only seen on polished cabochons. Chatoyant is the ability to exhibit chatoyancy.

A substance with a distinct molecular formation, produced by a chemical process.

chemical bond
A force by which atoms are bound in a molecule or crystal.

chemical formula
The scientific method of describing what elements a material is composed of.

chemical sediment
Sediment that is composed of previously dissolved minerals that have either precipitated from evaporated water or been extracted from water by living organisms and deposited when the organisms died or discarded their shells.

chemical structure
The atomic arrangement of a substance.

chemical weathering
The process by which chemical reactions alter the chemical composition of rocks and minerals that are unstable at the Earth's surface and convert them into more stable substances; weathering that changes the chemical makeup of a rock or mineral. See also mechanical weathering.

The study and science of the composition and structure of all substances.

A member of a group of sedimentary rocks that consist primarily of microscopic silica crystals. Chert may be either organic or inorganic, but the most common forms are inorganic.

Small nuggets of rocky material that exist in certain meteorites. These droplets of matter are believed to have condensed from our solar system's original nebula about five billion years ago. Their primary element is iron.

chromate (group)
Group of minerals that are compounds of one or more metallic elements combined with the chromate radical (CrO4). Minerals in this group are usually brightly colored and heavy. The chromates are rare minerals and are usually classified as a sub-group of the sulfates.

chrysoberyl twin
Form of contact twinning, in which six Chrysoberyl crystals join at the base, forming a six-pointed formation, as depicted in the figure below.

cinder cone
A pyroclastic cone composed primarily of cinders.

A deep, semi-circular basin eroded out of a mountain by an alpine glacier.

cirque glacier
A small alpine glacier that forms inside a cirque, typ-ically near the head of a valley.

Fragment of rock or mineral broken off from a large piece.

Being or pertaining to a sedimentary rock composed primarily from fragments of preexisting rocks or fossils.

A mixture of very fine grains of micaceous substances. Clay is plastic when wet and hardens when heated. It consists mainly of hydrous aluminum silicates.

The tendency of certain minerals to break along distinct planes in their crystal structures where the bonds are weakest. Cleavage is tested by striking or hammering a mineral, and is classified by the number of surfaces it produces and the angles between adjacent surfaces.

Type of cleavage exhibited on minerals of the isometric system that are crystallized as cubes. The method of cleavage is that small cubes break off of an existing cube.

Type of cleavage exhibited on some prismatic minerals in which the mineral cleaves by breaking off thin, vertical, prismatic crystals off of the original prism. Example is Acmite.

cleavage angle
The angle, or side, that exhibits or has exhibited cleavage.

cleavage fragment
Crystallized fragment that broke off of a mineral that exhibits cleavage.

cleaved surface
Broken surface of a mineral that has a flat surface where the mineral broke, proving that the mineral exhibits cleavage.

Describing an elongated crystal with a steep, slanted angle towards its top at the base. Minerals shaped this way are clinopinicoidal.

Dense agglomeration of crystals.

A member of a group of easily combustible, organic sedimentary rocks composed mostly of plant remains and containing a high proportion of carbon.

The area of dry land that borders on a body of water.

A thin layer of one mineral on the surface of another.

A high mountain pass that forms when part of an ar�te erodes.

The characteristic color or colors of a mineral.

Aggregate defining a mineral which has parallel, slender, compact, adjoining crystals.

The diagenetic process by which the volume or thickness of sediment is reduced due to pressure from overlying layers of sediment.

The ability of a given stream to carry sediment, measured as the diameter of the largest particle that the stream can transport. See also capacity.

composite cone
See stratovolcano.

The elements and the quantity of the elements a substance contains.

An electrically neutral substance that consists of two or more elements combined in specific, constant proportions. A compound typically has physical characteristics different from those of its constituent elements.

Stress that reduces the volume or length of a rock, as that produced by the convergence of plate margins.

Aggregate describing foliated masses that are somewhat spherical and rotate about a center; appearing like a rose (rosette). Also used to describe a form of banding where the bands are circular, forming rings about a central point.

conchoidal fracture
Mineral fracture in which the indentation resembles a shell.

Aggregate composed of a mass of small crystals that become cemented together, resulting in a rounded, odd form.

1) A substance capable of transmitting electricity, such as a metal. 2) Something that is able to retain a substance such as heat or pressure.

cone of depression
An area in a water table along which water has descended into a well to replace water drawn out, leaving a gap shaped like an inverted cone.

A clastic rock composed of particles more than 2 millimeters in diameter and marked by the roundness of its component grains and rock fragments.

contact metamorphism
Metamorphism which is caused from magma intrusion near the contact with the magma.

contact twinning
Form of twinning where two crystals join together at a base. Examples: japanese twin, spinel twin, and chrysoberyl twin.

continental collision
The convergence of two continental plates, resulting in the formation of mountain ranges.

continental drift
The hypothesis, proposed by Alfred Wegener, that today's continents broke off from a single supercontinent and then plowed through the ocean floors into their present positions. This explanation of the shapes and locations of Earth's current continents evolved into the theory of plate tectonics.

continental ice sheet
An unconfined glacier that covers much or all of a continent.

continental platform
Continental platforms are the regions adjacent to and surrounding the continental shields. They are typically a relatively thin veneer of sedimentary rock that buries the edges of the shields.

continental shield
Broad areas of exposed ancient crystalline rocks in the cores of the Earth's continents. These rocks are typically the oldest on the continentes, many more than 2.5 billion years old.

convection cell
The cycle of movement in the asthenosphere that causes the plates of the lithosphere to move. Heated material in the asthenosphere becomes less dense and rises toward the solid lithosphere, through which it cannot rise further. It therefore begins to move horizontally, dragging the lithosphere along with it and pushing forward the cooler, denser ma...

The coming together of two lithospheric plates. Convergence causes subduction when one or both plates is oceanic, and mountain formation when both plates are continental. See also divergence.

Fossilized animal excrement embedded in rock.

Marine polyp that secretes calcareous skeletons. The skeleton is also called coral, and is used as an ornamental stone.

The innermost layer of the Earth, consisting primarily of pure metals such as iron and nickel. The core is the densest layer of the Earth, and is divided into the outer core, which is believed to be liquid, and the inner core, which is believed to be solid. See also crust and mantle.

The process of determining that two or more geographically distant rocks or rock strata originated in the same time period.