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


isotropic
Synonym of monotropic.

isotropization
Radioactive decaying that causes destruction to a minerals crystal lattice.

isotype
Synonym of isomorph.

isotypism
Synonym of isomorphism.

isotypous
Synonym of isomorphous.

jagged fracture
Synonym of hackly fracture: Type of fracture resembling broken metal, exhibiting sharp, jagged surfaces.

japanese twin or japanese law twin
Form of contact twinning where two single Quartz crystals are joined by the their base at an angle near 90�.

jet
Coal that can be polished and used for ornamental purposes.

jetty
A structure built along the bank of a stream channel or tidal outlet to direct the flow of a stream or tide and keep the sediment moving so that it cannot build up and fill the channel. Jetties are typically built in parallel pairs along both banks of the channel. Jetties that are built perpendicular to a coast tend to interrupt longshore drift and...

jewel
A gem, whether cut or uncut, capable of being used as an ornament.

jeweler
Individual whose trade is to buy and sell jewels and gemstones.

joint
A fracture dividing a rock into two sections that have not visibly moved relative to each other. See also fault.

K. or Kt.
Abbreviation of karat.

karat
Unit of measurement describing the content of gold in an ornament. The karat unit measures the percentage of gold in metallic objects made of gold (mainly jewelry). Since pure gold bends too easily, it is mixed with tougher metals when made into ornaments to form a tougher, although impurer, gold. The karat measurement determines the percentag...

karst
A topography characterized by caves, sinkholes, disappearing streams, and underground drainage. Karst forms when groundwater dissolves pockets of limestone, dolomite, or gypsum in bedrock.

labradorescence
Effect which causes dark, metallic-like color shimmers, commonly blue and green, to be displayed on a few minerals. The name is derived from Labradorite, a mineral which is the best example of this effect.

laccolith
A large concordant pluton that is shaped like a dome or a mushroom. Laccoliths tend to form at relatively shallow depths and are typically composed of granite. The country rock above them often erodes away completely.

lahar
A flow of pyroclastic material mixed with water. A lahar is often produced when a snow-capped volcano erupts and hot pyroclastics melt a large amount of snow or ice.

lamellar
Synonym of scaly: Aggregate of small, flattened, overlapping crystals, as seen in fish scales.

laminated rock
Sedimentary rocks consisting of many thin layers.

lanthanides
Group of elements, very similar in chemical properties, once thought to be extremely rare. They take up numbers 57 through 71 on the periodical table. Also called rare earth elements.

lapidary
An individual who facets gemstones as a trade, and the shop of such an individual. Also used in adjective form when relating to gems.

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

lava
Magma that comes to the Earth's surface through a volcano or fissure.

leach
To dissolve from a rock. For example, when acidic water passes through fractured rocks, soluble minerals leach, or dissolve, from the rocks.

lenticular
Lens shaped. When applied to minerals it refers to concretions or nodules that have a flattened, lens-like shape.

levee
A protective barrier built along the banks of a stream to prevent flooding. See also natural levee.

lichen
Plant-like colonies of fungi and algae that grow on the exposed surface of rocks. Lichen grow at a constant rate within a single geographic area.

lichenometry
A method of numerical dating that uses the size of lichen colonies on a rock surface to determine the surface's age. Lich-enometry is used for rock surfaces less than about 9000 years old.

light
Type of electromagnetic radiation that oscillates between electric and magnetic fields, and can be detected by the human eye.

lignite
A soft, brownish coal that develops from peat through bacterial action, is rich in kerogen, and has a carbon content of 70%, which makes it a more efficient heating fuel than peat.

limestone
A sedimentary rock composed primarily of calcium carbonate. Some 10% to 15% of all sedimentary rocks are limestones. Limestone is usually organic, but it may also be inorganic.

liquefaction
The conversion of moderately cohesive, unconsolidated sediment into a fluid, water-saturated mass.

lithification
The conversion of loose sediment into solid sedimentary rock.

lithosphere
A layer of solid, brittle rock making up the outer 100 kilometers of the Earth, encompassing both the crust and the outermost part of the upper mantle. See also asthenosphere.

lithostatic pressure
The force exerted on a rock buried deep within the Earth by overlying rocks. Because lithostatic pressure is exerted equally from all sides of a rock, it compresses the rock into a smaller, denser form without altering the rock's shape.

litmus paper
Paper with powder extracted from certain plants that tests the pH of a substance. Acid turns red while base turns blue; neutral remains white. The stronger the acid or base, the more intense red or blue the color of the litmus paper turns.

locality
Area where a specific mineral was found or occurs.

lode
Vein of precious metal.

loess
A load of silt that is produced by the erosion of outwash and transported by wind. Much loess found in the Mississippi Valley, China, and Europe is believed to have been deposited during the Pleistocene Epoch.

longitudinal dune
One of a series of long, narrow dunes lying parallel both to each other and to the prevailing wind direction. Longi-tudinal dunes range from 60 meters to 100 kilometers in length and from 3 to 50 meters in height.

longshore current
An ocean current that flows close and almost parallel to the shoreline and is caused by the rush of waves toward the shore.

longshore drift
1. The process by which a current moves sediments along a surf zone. 2. The sediments so moved. Longshore drift typically consists of sand, gravel, shell fragments, and pebbles. See also beach drift.

longwave
A wavelength of ultraviolet light. Some minerals display fluorescence when exposed to longwave ultraviolet light. Commonly abbreviated as LW.

lopolith
A saucer-shaped intrusive body of igneous rock. Lopoliths are typically mafic in composition.

loupe
Small magnifying lens used to observe certain aspects of a gemstone. Loupes usually have a magnification level of 10x.

low-velocity zone
An area within the Earth's upper mantle in which both P waves and S waves travel at markedly slower velocities than in the outermost part of the upper mantle. The low-velocity zone occurs in the range between 100 and 350 kilometers of depth.

lubricant
Material that can reduce friction. Used as a coating on objects that are subject to friction.

luminesce
To give off light under certain conditions.

luminescence
General term describing the capability of a mineral with a habit of giving off light when put under certain conditions. Three examples of luminescence are fluorescence, triboluminescence, and thermoluminescence.

luminescent
General term describing any mineral capable of giving off light when put under certain conditions. Three examples of minerals that are luminescent are minerals that exhibit fluorescence, triboluminescence, and thermoluminescence.

luster
Luster of opaque to nearly opaque minerals with very good reflective properties.

m�lange
A body of rock that forms along the inner wall of an ocean trench and is made up of fragments of lithosphere and oceanic sediment that have undergone metamorphism.

macrocrystalline
Having crystals large enough to be seen with an unaided eye.

mafic
Describing dark colored rocks or minerals that are composed particularly of magnesium and iron.

magma
Molten (melted) rock that forms naturally within the Earth. Magma may be either a liquid or a fluid mixture of liquid, crystals, and dissolved gases.

magmatic
Igneous

magmatite
Term describing any igneous rock.

magnesia
1) Industrial material made of magnesium oxide. 2) Describing a mineral that is composed of magnesium oxide.

magnet
An object that is surrounded by a magnetic field, causing iron or steel materials to be attracted to it.

magnetic field
The region within which the magnetism of a given substance or particle affects other substances.

magnetic field
Area encompassing a magnet or electric current which has the ability to attract or repel certain objects anywhere in the field. Points in the magnetic field closer to the magnet or electrical current are stronger, and points further away are weaker.

magnetic reversal
The process by which the Earth's magnetic north pole and its magnetic south pole reverse their positions over time.

magnetism
The property, possessed by certain materials, to attract or repel similar materials. Magnetism is associated with moving electricity.

malleable
Ability of a certain minerals that are able to be pounded into thin sheets.

mammilary
Aggregate describing smooth, rounded, agglomerations. Rounded agglomerations of mammilary aggregates are larger than reniform agglomerations and considerably larger than botryoidal agglomerations.

mantle
The middle layer of the Earth, lying just below the crust and consisting of relatively dense rocks. The mantle is divided into two sections, the upper mantle and the lower mantle; the lower mantle has greater density than the upper mantle. See also core and crust.

marble
A coarse-grained, nonfoliated metamorphic rock derived from limestone or dolostone.

marine magnetic anomaly
An irregularity in magnetic strength along the ocean floor that reflects sea-floor spreading during periods of magnetic reversal.

massive
Term used to describe a rock or mineral that has no particular shape, either because it is non-crystalline; it is composed of tiny, unorganized crystals; it is a shapeless fragment of a crystal. A massive sulfide deposit is an unusually large deposit of sulfide minerals.

matrix
A material that has an embedded crystal inside or emerging from it.

meandering stream
A stream that traverses relatively flat land in fairly evenly spaced loops and separated from each other by narrow strips of floodplain.

mechanical exfoliation
A form of mechanical weathering in which successive layers of a large plutonic rock break loose and fall when the erosion of overlying material permits the rock to expand upward. The thin slabs of rock that break off fall parallel to the exposed surface of the rock, creating the long, broad steps that can be found on many mountains.

mechanical weathering
The process by which a rock or mineral is broken down into smaller fragments without altering its chemical makeup; weathering that affects only physical characteristics. See also chemical weathering.

melting point
The temperature it takes a certain material to change from a solid to liquid state.

Mercalli intensity scale
A scale designed to measure the degree of intensity of earthquakes, ranging from I for the lowest intensity to XII for the highest. The classifications are based on human perceptions.

mesothermal vein
Vein created due to intense heat (in range from around 390� to 570� F [200� to 300� C] ).

Mesozoic Era
The intermediate era of the Phanerozoic Eon, following the Paleozoic Era and preceding the Cenozoic Era, and marked by the dominance of marine and terrestrial reptiles, and the appearance of birds, mammals, and flowering plants.

metal
Any of a category of electropositive (positively charged) elements or combinations of them in the form of minerals that exhibit a metallic luster, malleability, ductility, and conductivity.

metallic
Having the attributes of a metal. Sometimes can be used to describe a mineral with a metallic luster even though it is not a true metal.

metallic bonding
The act or process by which two or more atoms of electron-donating elements pack so closely together that some of their electrons begin to wander among the nuclei rather than orbiting the nucleus of a single atom. Metallic bonding is responsible for the distinctive properties of metals.

metallic elements
The metallic elements are minerals belonging to the native elements group. They consist of minerals that are pure elements or metallic alloys. They are all true metals, that is they have a metallic luster, are malleable and ductile, and are good conductors of electricity.

metallic luster
Exhibiting the luster of a metal, which is opaque and reflective. Some minerals exhibit a metallic luster even though they are not true metals.

metallurgy
The science and procedures involved in extracting metals from ore, refining the metals, blending them into alloys, and fashioning useful objects from them. Three forms of metallurgy are hydrometallurgy, electrometallurgy, and pyrometallurgy.

metamic
Crystalline minerals that lose their crystal structure due to radioactive destruction.

metamorphic differentiation
The process by which minerals from a chemically uniform rock separate from each other during metamorphism and form individual layers within a new metamorphic rock.

metamorphic grade
A measure used to identify the degree to which a metamorphic rock has changed from its parent rock. A metamorphic grade provides some indication of the circumstances under which the metamorphism took place.

metamorphic index mineral
One of a set of minerals found in metamorphic rocks and used as indicators of the temperature and pressure conditions at which the metamorphism occurred. A metamorphic index mineral is stable only within a narrow range of temperatures and pressures, and the metamorphism that produces it must take place within that range.

metamorphic rock
A rock that has undergone chemical or structural changes. Heat, pressure, or a chemical reaction may cause such changes.

metamorphism
The process by which conditions within the Earth, below the zone of diagenesis, alter the mineral content, chemical composition, and structure of solid rock without melting it. Igneous, sedimentary, and metamorphic rocks may all undergo metamorphism.

metasilicate chains
Synonym of inosilicates: Group of silicate minerals that have their tetrahedrons form single or multiple chains, with two oxygen atoms of each tetrahedron part of its neighboring tetrahedron forming long, thin, chains.

metasilicate rings
Synonym of cyclosilicates: 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.

metasilicates
This term either refers to the metasilicate chains (inosilicates), the metasilicate rings (cyclosilicates), are both the metasilicate chains and rings.

metasomatism
The chemical alteration of rocks or minerals by interaction with liquids. The alteration must only take place if the rock or mineral was not in a molten state in order for it to be metasomatism.

metastable
Describing the condition of radioactive minerals which cannot withstand their composition and begin to decay. Also refers to minerals that crystallize at a certain temperature and can only retain the initial crystal structure at certain temperatures. Synonym of unstable.

meteoric water
The precipitation of condensed water from clouds as rain, snow, sleet, or hail.

meteorite
Meteor that did not fully burn up in the atmosphere and landed on the earth.

meteoroid
Solid mass suspended in outer space that revolves around the sun. Meteoroids are smaller than asteroids.

micaceous
Aggregate of compact, flat, parallel, flexible, and peelable sheets, or describing minerals that occur in such aggregates.

microcontinent
A section of continental lithosphere that has broken off from a larger, distant continent, as by rifting.