Copy of `Inland Lapidary - Gem glossary`
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Inland Lapidary - Gem glossary
Category: General technical and industrial > Gems and Geology
Date & country: 27/10/2013, USA
Words: 1119
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pyramidal Shaped as a pyramid.
pyritohedraon Twelve sided polyhedron; all sides are equidimensional and pentagonal. Minerals shaped as pyritohedrons belong to the isometric system.
pyroclastic Being or pertaining to rock fragments formed in a volcanic eruption.
pyroclastic cone A usually steep, conic volcano composed almost entirely of an accumulation of loose pyroclastic material. Pyro-clastic cones are usually less than 450 meters high. Because no lava binds the pyroclastics, pyroclastic cones erode easily.
pyroclastic eruption A volcanic eruption of viscous, gas-rich magma. Pyroclastic eruptions tend to produce a great deal of solid volcanic fragments rather than fluid lava.
pyroclastic flow A rapid, extremely hot, downward stream of pyroclastics, air, gases, and ash ejected from an erupting volcano. A pyroclastic flow may be as hot as 800�C or more and may move at speeds exceeding 150 kilometers per hour.
pyroclastics (used only in the plural) Particles and chunks of igneous rock ejected from a volcanic vent during an eruption.
pyroelectric Substance that generates an electrical charge during a temperature change.
pyroelectricity Electricity generated when a pyroelectric substance is put under temperatures in which it will generate electricity.
pyrometallurgy The separation of metals from ore or from alloys through a process dependent on heat, or the forming of alloys and purification of metals through a process dependent on heat.
pyrosilicattes Synonym of sorosilicates
quarry Mine in which minerals or ore is blasted out of the side of a mountain or hill.
quartz group Synonym of Silica group
quartzite An extremely durable, nonfoliated metamorphic rock derived from pure sandstone and consisting primarily of quartz.
Quaternary ice age An ice age that began approximately 1.6 million years ago and continues to the present time.
radiating Aggregate composed of tiny, slender crystals compacted together radiating from a central point. The radiation can be flat or three dimensional. If three dimensional, this aggregate commonly occurs with circular, ball-like masses, and is known as spherulitic
radiation The emission of alpha, beta, or gamma rays.
radical Compounds that act as a single atom when combining with other elements to form minerals. Radicals contain one or more unpaired electrons.
radioactive 1) Term given to describe substances that contain atoms whose nuclei are are unstable, which causes the substance to slowly decay and emit radiation. Radioactive minerals usually take an extremely long time to decay if kept in proper settings. 2) (verb) - Emitting alpha, beta, and gamma rays.
radioactivity The effect of radioactive material, emitting alpha, beta, and gamma rays. Also used to describe in present tense the nature of radioactive material.
rain shadow effect The result of the process by which moist air on the windward side of a mountain rises and cools, causing precipitation and leaving the leeward side of the mountain dry.
rare earth (elements) 1) 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 known as the lanthanides.1) The rare earth elements. 2) Oxides of the rare earth elements.
recrystallization The diagenetic process by which unstable minerals in buried sediment are transformed into stable ones.
reflection The event occurring when light hits a material and bounces off of it. There are different degrees of reflection, the strongest being light rays bouncing off a smooth, flat, polished surface, such as a mirror, where they bounce off and form a reversed image on the surface. Polished Hematite is a great example describing a reflective mineral, wh...
refract Bend.
refraction The bending of white light upon entering a new dimension, such as from air to water or from air to a crystal, and splitting the white light into the colors of the spectrum.
refractive index The amount of refraction that takes place in a particular substance, which is a direct connection to the speed of light in that substance. The higher the refractive index, the greater the amount of dispersion, which increase the brilliance of a material. The refractive indices of gems are measured with a refractometer. Gems can be identified b...
refractometer Instrument that measures the refraction of light when it enters through a different dimension, such as from air to water or from air into a crystal.
regional metamorphism Metamorphism that affects rocks over vast geographic areas stretching for thousands of square kilometers.
relative dating The fixing of a geologic structure or event in a chronological sequence relative to other geologic structures or events. See also numerical dating.
relative density Synonym of specific gravity
reniform Aggregate describing smooth, rounded, kidney-like agglomerations. Rounded agglomerations of reniform aggregates are larger than botryoidal agglomerations but smaller than mammilary agglomerations.
repeated twinning Form of twinning where two or more crystals form a repeated pattern. Examples: cassiterite twin, rutile twin, plagioclase twin, and fishtail twin.
replace/replacement Having some or all the atoms being exchanged for atoms of a similar element. The process of one mineral taking the place of another mineral or material, with one or two atoms per molecule in the structure being exchanged with a different one with similar characteristics, thus creating a new mineral that retains the shape of the first mineral. ...
reserve A known resource that can be exploited for profit with available technology under existing political and economic conditions.
reservoir rock A permeable rock containing oil or gas.
resinous luster Luster describing yellow, dark orange, or brown minerals with slightly high refractive indices -- honey like, but not necessarily the same color.
resistance The unyielding of material to destructive acids and tough environments
resource A mineral or fuel deposit, known or not yet discovered, that may be or become available for human exploitation.
reticulated Aggregate composed of long crystals in a netting-like form, where all the crystals crisscross each other.
reverse fault A dip-slip fault marked by a hanging wall that has moved upward relative to the footwall. Reverse faults are often caused by the convergence of lithospheric plates.
rhomb-scalenohedron Mixture of a rhombohedron and a scalenohedron.
rhombic dodecahedron See dodecahedron
rhombohedral clevage Type of cleavage exhibited on minerals that crystallize in the hexagonal system and as rhombohedrons, in which small rhombohedrons cleave off of the existing rhombohedron. Example is Calcite.
rhombohedron Six sided polyhedron with each side shaped as a rhombus.
rhyolite Any of a group of felsic igneous rocks that are the extrusive equivalents of granite.
Richter scale A logarithmic scale that measures the amount of energy released during an earthquake on the basis of the amplitude of the highest peak recorded on a seismogram. Each unit increase in the Richter scale represents a 10-fold increase in the amplitude recorded on the seismogram and a 30-fold increase in energy released by the earthquake. Theoretic...
rift Crack in a rock. On a large scale it refers to the separation of plates on fault areas, forming a depression in the earth.
rifting The tearing apart of a plate to form a depression in the Earth's crust and often eventually separating the plate into two or more smaller plates.
ring silicates Same as 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.
rip current A strong, rapid, and brief current that flows out to sea, moving perpendicular to the shoreline.
ripple marks A pattern of wavy lines formed along the top of a bed by wind, water currents, or waves.
riprap A pile of large, angular boulders built seaward of the shoreline to prevent erosion by waves or currents. See also seawall.
rock A naturally formed aggregate of an indefinite mixture of naturally occurring substances, mainly minerals. Its composition may vary in containment of minerals and organic substances, and are never exact.
rock crystal Transparent, colorless, crystal of Quartz.
rock cycle A series of events through which a rock changes, over time, between igneous, sedimentary, and metamorphic forms.
rock shop Commercial store where minerals and rough gemstones can be purchased.
rock show Periodical show in a large, usually indoor arena where mineral and gem dealers come to sell their stock at wholesale prices.
rock-forming mineral One of the 20 or so minerals contained in the rock that composes the Earth's crust and mantle.
rosette Mineral with concentric aggregates resembling rose flowers.
rough Without any crystal faces. In regard to gemstones it refers to unfaceted material.
rubidium-strontium dating A form of radiometric dating that relies on the 47-billion-year half-life of radioactive isotopes of rubidium, which decay into isotopes of strontium, to determine the age of rocks in which strontium is present. Rubidium-strontium dating is used for rocks that are at least 10 million years old, deep-Earth plutonic rocks, and Moon rocks.
rust Powdery or crusty, brownish-yellow coating of iron oxides commonly see on iron materials after they come in contact with water.
rusting Developing a coat of rust on the surface, or containing a rust coating from a previous rusting.
rutilated Containing the needle like mineral Rutile as impurities.
S-wave shadow zone The region within an arc of 154� directly opposite an earthquake's epicenter that is marked by the absence of S waves. The S-wave shadow zone is due to the fact that S waves cannot penetrate the liquid outer core. See also P-wave shadow zone.
saccharroidal Composed of tiny, equi-dimensional crystals that resemble grains of sugar.
saline Containing salt.
saline deposit Mineral environment containing minerals formed through partial or full evaporation of a mineral-rich, saline lake.
saline lake Mineral-rich lake found in arid regions that contains a heavy salt content, and frequently contains evaporate minerals which form as the lake evaporates. Saline lakes may fully evaporate, in which they become dry lakes.
salinity Amount of salt present.
salt 1) Compound formed when a metal partially or fully takes the place of hydrogen in an acid. 2) The mineral Halite.
salt dome Separated fold in an anticline which is plugged up with a mass of salt.
sand Accumulation of small grains of rock, usually found at beaches and in desert regions.
sandstone A clastic rock composed of particles that range in diameter from 1/16 millimeter to 2 millimeters in diameter. Sandstones make up about 25% of all sedimentary rocks.
scalenohedron Six sided polyhedron, similar to a bipyramidal hexagon, but the adjoining area at the center is diagonal between every side as opposed to being level. Other modifications might be present. Minerals shape this way are scalenohedral.
scales Aggregate of small, flattened, overlapping crystals, as seen in fish scales.
scaly Describing an aggregate of scales.
scarp The steep cliff face that is formed by a slump.
scepter Crystal deformity where the top part of a prismatic crystal protrudes and is wider than the rest of the crystal.
schist A coarse-grained, strongly foliated metamorphic rock that develops from phyllite and splits easily into flat, parallel slabs. Type of metamorphic rock made up of parallel layers of flaky, micaceous minerals.
scientific law 1. A natural phenomenon that has been proven to occur invariably whenever certain conditions are met. 2. A formal statement describing such a phenomenon and the conditions under which it occurs. Also called law.
scientific methods Techniques that involve gathering all available data on a subject, forming a hypothesis to explain the data, conducting experiments to test the hypothesis, and modifying or confirming the hypothesis as necessary to account for the experimental results.
sclerometer Instrument used to determine the absolute hardness of a mineral. A mineral is locked into position , and a Diamond pin pushes down and slightly scratched the mineral. The amount of pressure needed for the Diamond pin to be pushed down to scratch the mineral determines its hardness.
sea arch A landform produced by coastal erosion of a prominent headland. Sea arches form when sea caves are excavated so deeply by crashing waves that two caves eroding on opposite sides of the headland become joined. The overlying rocky roof is left as an arch.
sea cave The notches in the sides of a prominent coastal rocky headland eroded by crahing waves.
sea stack A steep, isolated island of rock, separated from a headland by the action of waves, as when the overhanging section of a sea arch is eroded.
sea-floor spreading The formation and growth of oceans that occurs following rifting and is characterized by eruptions along mid-ocean ridges, forming new oceanic lithosphere, and expanding ocean basins. See also divergence.
seamount A conical underwater mountain formed by a volcano and rising 1000 meters or more from the sea floor.
seawall A wall of stone, concrete, or other sturdy material, built along the shoreline to prevent erosion even by the strongest and highest of waves. See also riprap.
secondary Altered to create a new mineral.
secondary coast A coast shaped primarily by erosion or deposition by sea currents and waves.
secondary enrichment The process by which a metal deposit becomes concentrated when other minerals are eliminated from the deposit, as through dissolution, precipitation, or weathering.
secondary mineral Mineral altered to a new form after undergoing a chemical change. An example is a mineral in the oxidation zone that transformed into another mineral through weathering.
secondary wave) A body wave that causes the rocks along which it passes to move up and down perpendicular to the direction of its own movement. See also P wave.
sectile Able to be cut into by a knife or other sharp object. A form of tenacity.
sediment A collection of transported fragments or precipitated materials that accumulate, typically in loose layers, as of sand or mud.
sedimentary environment The continental, oceanic, or coastal surroundings in which sediment accumulates.
sedimentary facies 1. A set of characteristics that distinguish a given section of sedimentary rock from nearby sections. Such characteristics include mineral content, grain size, shape, and density. 2. A section of sedimentary rock so characterized.
sedimentary rock A rock made from the consolidation of solid fragments, as of other rocks or organic remains, or by precipitation of minerals from solution.
