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

A form of mechanical weathering that occurs when loose fragments or particles of rocks and minerals that are being transported, as by water or air, collide with each other or scrape the surfaces of stationary rocks.

Hard, tough material used to smooth out rough surfaces; a common abrasive is sandpaper.

absolute hardness
Scale for measuring the hardness of a mineral. The Mohs scale also measures hardness, except the absolute hardness scale has its numbers in proportion. Only scientists use the absolute hardness scale; mineral collectors measure hardness using the Mohs scale.

absorption spectrum
The specific bands of light that pass through and those that get absorbed in a gem or mineral and disperse into the colors of the spectrum. Different gems have different absorption spectra, meaning they are all unique in regard to which colors are absorbed and which pass through. This plays a major role in identifying gems, and can easily distingui...

wedge A mass of sediment and oceanic lithosphere that is transferred from a subducting plate to the less dense, overriding plate with which it converges.

Any of a group of chemicals containing a free hydrogen element. Certain acids are used to clean minerals, and tests can be performed on some minerals with certain acids.

(HF) Corrosive acid used for the production of glass(, since it dissolves glass). It is a very destructive liquid and will some many minerals.

acid rain
Rain that contains such acidic compounds as sulfuric acid and nitric acid, which are produced by the combination of atmospheric water with oxides released when hydrocarbons are burned. Acid rain is widely considered responsible for damaging forests, crops, and human-made structures, and for killing aqua-tic life.

acid test
Procedure performed to help identify a mineral. Certain acids (usually hydrochloric acid and nitric acid) are placed in contact with the mineral or its powder, and, depending on the mineral, it dissolves, effervesces, or remains inactive.

Particle in a fluorescent substance that causes the substance to glow when exposed to ultraviolet light.

Pertaining to luster. Transparent minerals with a very high luster are said to have an adamantine luster.

An effect seen on certain minerals which causes it to display a billowy, rounded, ghost-like reflection with a bluish-whitish color emanating from the surface when the mineral is cut into a cabochon. It is caused by structural anomalies or build up of water in the mineral. The minerals most famous for exhibiting adularescence are Opal and Moonstone...

The effect caused by small inclusions of a mineral with a highly reflective surface (commonly Hematite, Pyrite, or Goethite) which causes it to exhibit a glistening effect, as if it is pasted with glitter, when rotated or looked at different points. The name is derived from Aventurine, a green variety of Quartz that exhibits this effect.

A ground tremor caused by the repositioning of rocks after an earthquake. Aftershocks may continue to occur for as long as two years after the initial earthquake. The intensity of an earthquake's aftershocks decreases over time.

The process by which a stream's gradient steepens due to increased deposition of sediment.

A grouping of crystals. Aggregates are defined by the ways crystals are clustered together.

Describing a chemical substance that is either a hydroxide, carbonate, or metal oxide that has the ability to turn litmus paper blue, and the ability to react with acids to form salts.

A metal that is manufactured by combining two or more molten metals. An alloy is always harder than its component metals. Bronze is an alloy of copper and tin.

Mixed with another metal to form an alloy.

alluvial fan
A triangular deposit of sediment left by a stream that has lost velocity upon entering a broad, relatively flat valley.

alluvium (alluvial)
Eroded material that gets carried downstream by the current of the stream or river. Alluvial deposits are areas in streams or rivers where alluvium does not continue flowing downstream, thus forming a deposit.

alpine cavity
synonym of vug, a cavity in rock that is lined with long, slender crystals. A vug forms when air pockets form in cooling magma and allow crystals to form in the hollow area

alpine glacier
A mountain glacier that is confined by highlands.

To physically transform from one mineral into another. Process is alteration

Any alloy of mercury and another metal. Some amalgams occur naturally. Note: There is a mineral known as Amalgam, and, although it is an amalgam, should not be confused with the term amalgam.

Fossilized pine resin, many times used for ornamental purposes.

Without a crystalline shape.

amphibole group (amphibole)
Group of minerals that contain iron, magnesium, silicon, oxygen, and hydroxyl (OH). They may also contain calcium, sodium, and lithium. The amphiboles have prismatic cleavage, and one can note the angle of 56� and 124�, which distinguishes it pyroxenes, which are at 87� and 93� (almost perpendicular). The amphiboles are very similar to the pyroxene...

A small, bubble-like mass formed from volcanic igneous rock that solidified and a bubble of gas got trapped in the interior.

The dark, aphanitic, extrusive rock that has a silica content of about 60% and is the second most abundant volcanic rock. Andesites are found in large quantities in the Andes Mountains

angle of repose
The maximum angle at which a pile of unconsolidated material can remain stable.

Without water. Anhydrous minerals contain no water in their chemical structure. The term anhydrous is usually used in reference to an anhydrous mineral belonging to a group which contains many hydrous minerals.

Neutral atom that gains an electron and becomes negatively charged.

Lacking consistent hardness on all surfaces. For example, the hardness of Kyanite on the Mohs scale is between 6 and 7 lengthwise, and between 4 and 4� crosswise

A hard, jet-black coal that develops from lignite and bituminous coal through metamorphism, has a carbon content of 92% to 98%, and contains little or no gas. Anthracite burns with an extremely hot, blue flame and very little smoke, but it is difficult to ignite and both difficult and dangerous to mine.

A convex fold in rock, the central part of which contains the oldest section of rock. See also syncline.

Group of sulfides that contain one or more true metals combined with the semi-metal antimony.

aqua fortis
Synonym of nitric acid

aqua regia
HCl),(HNO3) Mixture of hydrochloric and nitric acids. It is an extremely destructive mixture and can dissolve gold and platinum, as well as many other minerals.

Formed from precipitating hard water. Stalagmites and stalactites are common examples.

An impermeable body of rock that may absorb water slowly but does not transmit it.

A permeable body of rock or regolith that both stores and transports groundwater.

A layer of rock having low permeability that stores groundwater but delays its flow.

A sharp ridge of erosion-resistant rock formed between adjacent cirque glaciers.

Synonym to dendritic: 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 (sing...

Containing silver.

Composed mostly of clay.

A dry, desert region. Many minerals that exist only in arid regions are usually the result of evaporation.

index The ratio of a region's potential annual evaporation, as determined by its receipt of solar radiation, to its average annual precipitation.

arragonite group
Group of minerals belonging to the carbonate group that are isomorphous with one another. They all crystallize in the orthorhombic system, exhibit good cleavage (although not as good as the members of the calcite group), have a weak double refraction in transparent specimens, and commonly intergrow in three individuals forming six sided trillings. ...

A small, deep, usually dry channel eroded by a short-lived or intermittent desert stream.

Group of minerals that are compounds of one or more metallic elements associated with the arsenate radical (AsO4). The arsenates, together with the related vanadates, are classified in the phosphate group. Most arsenates are heavy, and none are hard. They are usually brittle and occur in small crystals or compact aggregates.

(subgroup) Group of sulfides that contain one or more true metals combined with the semi-metal arsenic.

Of, being, or concerning an aquifer in which water rises to the surface due to pressure from overlying water.

Fibrous minerals of the amphibole group, as well as fibrous Serpentine, are known as asbestos.

asbestos amphibole
Any extremely fibrous mineral of the amphibole group

Effect exhibited on some minerals (usually only in polished cabochons) causing it to reflect a billowy, star-like formation of concentrated light which moves around when the mineral is rotated. Asterism is caused by dense inclusions of tiny, parallel, slender, fibers in the mineral which cause the light to reflect in such an interesting manner. Min...

Large solid mass suspended in outer space that revolves around the sun. Asteroids are larger than meteoroids.

A layer of soft but solid, mobile rock comprising the lower part of the upper mantle from about 100 to 350 kilometers beneath the Earth's surface. See also lithosphere.

Not containing perfect symmetry.

A circular reef that encloses a relatively shallow lagoon and extends from a very great depth to the sea surface. An atoll forms when an oceanic island ringed by a barrier reef sinks below sea level.

The smallest particle that retains all the chemical properties of a given element.

atomic mass
1. The sum of protons and neutrons in an atom's nucleus. 2. The combined mass of all the particles in a given atom.

atomic number
The number of protons in the nucleus of a given atom. Elements are distinguished from each other by their atomic numbers.

atomic structure
The arrangement and the type of atoms that exist in a particular substance.

Containing gold.

Describing a rock or mineral that formed in the same location where it was found.

The effect caused by small inclusions of a mineral with a highly reflective surface (commonly Hematite, Pyrite, or Goethite) which causes it to exhibit a glistening effect, as if it is pasted with glitter, when rotated or looked at different points. The name is derived from Aventurine, a green variety of Quartz that exhibits this effect.

Imaginary line drawn through the center of an object, either horizontally or vertically. In the case of minerals, it is used to determine if and how mineral has symmetry. The horizontal axis is known as the x axis, the vertical axis as the y axis. Axis lines are usually drawn as dotted lines. Plural is axes.

backarc basin
A depression landward of a volcanic arc in a subduction zone, which is lined with trapped sediment from the volcanic arc and the plate interior. See also forearc basin.

backarc spreading
The process by which the overriding plate in a subduction zone becomes stretched to the point of rifting, so that magma can then rise into the gap created by the rift. Backarc spreading typically occurs when the subducting plate sinks more rapidly than the overriding plate moves forward.

The portion of a beach that extends from the high-tide line inland to the sea cliff or vegetation line. Swash reaches the backshore only during major storms.

The section of a floodplain where deposits of fine silts and clays settle after a flood. Backswamps usually lie behind a stream's natural levees.

banded iron formation
A rock that is made up of alternating light silica-rich layers and dark-colored layers of iron-rich minerals, which were deposited in marine basins on every continent about 2 billion years ago.

barchan dune
A crescent-shaped dune that forms around a small patch of vegetation, lies perpendicular to the prevailing wind direction, and has a gentle, convex windward slope and a steep, concave leeward slope. Barchan dunes typically form in arid, inland deserts with stable wind direction and relatively little sand.

barrier island
A ridge of sand that runs parallel to the main coast but is separated from it by a bay or lagoon. Barrier islands range from 10 to 100 kilometers in length and from 2 to 5 kilometers in width. A barrier island may be as high as 6 meters above sea level. barrier reef A long, narrow reef that runs parallel to the main coast but is separated from it b...

Having to do with the base.

basal sliding
The process by which a glacier undergoes thawing at its base, producing a film of water along which the glacier then flows. Basal sliding primarily affects glaciers in warm climates or mid-latitude mountain ranges.

The dark, dense, aphanitic, extrusive rock that has a silica content of 40% to 50% and makes up most of the ocean floor. Basalt is the most abundant volcanic rock in the Earth's crust.

base level
The lowest level to which a stream can erode the channel through which it flows, generally equal to the prevailing global sea level.

Constructed of alkaline components. When seen in the composition of a mineral, it refers to the hydroxyl radical.

A round or oval depression in the Earth's surface, containing the youngest section of rock in its lowest, central part.

A massive discordant pluton with a surface area greater than 100 square kilometers, typically having a depth of about 30 kilometers. Batholiths are generally found in elongated mountain ranges after the country rock above them has eroded.

baymouth bar
A narrow ridge of sand that stretches completely across the mouth of a bay. (Also called bay bar and bay barrier.)

The part of a coast that is washed by waves or tides, which cover it with sediments of various sizes and composition, such as sand or pebbles.

beach drift
1. The process by which swash and backwash move sediments along a beach face. 2. The sediments so moved. Beach drift typically consists of sand, gravel, shell fragments, and pebbles. See also longshore drift.

beach face
The portion of a foreshore that lies nearest to the sea and regularly receives the swash of breaking waves. The beach face is the steepest part of the foreshore.

bead test
Complex, scientific test which is conducted to identify a mineral. A mineral is crushed and mixed into a borax flux, and is heated until a glassy bead forms. The bead is then touched by the crushed mineral powder and one of several colors appears on the bead, depending on the metallic elements of the mineral. The colors are different in most cases ...

1) Rock mass of one type surrounded by a different type of rock. 2) A deposit of granular rock caused from erosion of solid rock.

bed load
A body of coarse particles that move along the bottom of a stream.

bed rock
Layer of solid rock underneath the soil.

The division of sediment or sedimentary rock into parallel layers (beds) that can be distinguished from each other by such features as chemical composition and grain size.

Benioff-Wadati zone
A region where the subduction of oceanic plates causes earthquakes, the foci of which are deeper the farther inland they are.

A low, narrow layer or mound of sediment deposited on a backshore by storm waves.

beta rays
Form of electromagnetic radiation in which the electromagnetic waves are composed of uncombined electrons

biogenic chemical sediment
Sedimentary rocks derived from living organisms. Common examples include fossiliferous limestones and coal.

biomass fuel
A renewable fuel derived from a living organism or the by product of a living organism. Biomass fuels include wood, dung, methane gas, and grain alcohol.

Crystal shape in form with a plane dividing a crystal into two pyramids base to base. Crystals exhibiting this are described as bipyramidal.

bipyramidal hexagon
Six sided polyhedron with all sides protruding out of the top and bottom points, forming a wide center. A bipyramidal hexagonal prism has a straight center. Crystals of this shape are a bypyramid hexagon.

Any of a group of solid and semi-solid hydrocarbons that can be converted into liquid form by heating. Bitumens can be refined to produce such commercial products as gasoline, fuel oil, and asphalt.