Glossary of Terms Tips

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What is faceting?


Cutting and polishing of the surfaces of a gemstone into facets. The number and shape of the facets give the stone its style of cut.

What does trichroic mean?


Refers to a gem that appears three different colors or shades when viewed from different directions.

What is a secondary deposit?

Secondary Deposit

Gems or minerals that have been separated from their original rock and redeposited elsewhere.

What is placer deposit?

Placer Deposit

Concentrated (secondary) deposit of minerals, usually in rivers or seas.

What is a geode?


Cavity within a rock, in which crystals line the inner surface and grow toward the center.

What does amorphous mean?


Without a regular internal atomic structure or external shape. Examples are glass, opal, or amber.

What is a spectroscope?


Instrument used to view the absorption spectra of gemstones.

What is schiller?


A form of platy iridescence.

What is opalescence?


Milky blue form of iridescence.

What is Moh´s scale of hardness?

Moh's Scale of Hardness

Measure of a mineral's hardness in relation to other minerals, based on its ability to resist scratching.

What is birefraction?


The difference between the highest and lowest refractive indices in doubly refractive gems.

What does allochromatic mean?


Refers to gems colored by impurities, without which the gem would be colorless.

What is annealing?


A heat treatment of metal that realigns its crystalline structure to its natural, more malleable state. Annealing removes stresses created in manipulation during the work process.

What is refraction?


Bending of light as it passes from air into a different medium.

What is fancy cut?

Fancy Cut

Name applied to a stone given an unconventional shape when cut.

What is an alloy?


The result of combining two or more metals, or a metal and a chemical element. For example, sterling silver is an alloy composed of pure silver and copper.

What is a drawplate?


A plate of hardened steel with holes of graduated sizes through which wire is pulled to alter its dimension.

What is centrifugal casting?

Centrifugal Casting

A casting technique whereby molten metal is thrust into a mold by centrifugal force. The most common method is by means of a spring driven arm supporting a crucible and a mold flask.

What is a species?


Individual gems that have distinct characteristics which may be defined and verified.

What is a sedimentary rock?

Sedimentary Rock

Rocks formed by the consolidation and hardening of rock fragments, organic remains, or other material.

What is metamict?


Refers to material that is breaking down from a crystalling to amorphous state, due to the presence of radioactive elements.

What is luster?


Shine or "look" of a gemstone due to reflection of light off the surface.

What are buffs?


Buffs are usually layered cotton, muslin, felt or leather layered and mounted on a motor driven spindle. Buffs are charged with abrasive compounds and spun against surfaces to cut and polish and buff the metal.

What is a synthetic gemstone?

Synthetic Gemstone

Laboratory made stone whose chemical composition and optical properties are similar to those of its natural equivalent.

What is a stone?


Term used for any gemstone.

What is a doublet?


Composite stone made of two pieces cemented or glued together.

What is primary deposit?

Primary Deposit

Material still in its original rock.

What is intergrown?


When two or more minerals grow together and become interlocked.

What is habit?


Shape in which a crystal naturally occurs.

What is an intaglio?


Design in which the subject is cut lower than the background.

What are inclusions?


Markings or foreign bodies found within a stone. Some can be used to identify a particular species.

What is a composite stone?

Composite Stone

Stone assembled from several pieces, often to imitate a gem.

What is a cabochon?


Gem cut and polished to have a domed outer surface. Such stones are said to be cut en cabochon.

What is the axis of symmetry?

Axis of Symmetry

Imaginary line through a crystal. If the crystal were rotated about its axis, it would present an identical aspect two or more times in a rotation of 360 degrees.

What is a carat?


A unit of measure used to determine the weight of gemstones - one carat equals 200 milligrams.

What is a refractometer?


Apparatus used to measure the refractive indices of gems.

What is an imitation gemstone?

Imitation Gemstone

Material that has the outward appearance of the gem it is intended to imitate, but which has different physical properties.

What is an alluvial deposit?

Alluvial Deposits

Concentrations of material that have been separated by weathering from the host rock, then deposited by rivers or streams.

What is chasing?


A surface embellishment technique applied to the front of a form. Chasing punches are commonly used to refine or delineate the front of cast or repousse` decorated work.

What is pavilion?


Lower part of a cut stone, below the girdle.

What is paste?


Glass made to imitate gems.

What does hydrothermal mean?


Refers to processes that involve the alteration or deposition of minerals by water heated by igneous activity.

What is a dapping punch?

Dapping Punch

A punch with a spherical work tip. It is used to form domed pieces from discs of flat sheet metal. The metal is tapped into a steel dapping block that has hemispherical recesses.

What is intrusive?


Igneous rock that has solidified within other rocks, below the Earth's surface.

What is cryptocrystalline?


Mineral structure in which crystals are so small they are not distinguishable with a microscope.

What is a conchoidal fracture?

Conchoidal Fracture

Shell like fracture.

What is an annealing booth?

Annealing Booth

An enclosed area designed to keep light off the workpiece during the annealing process. The metal's color or annealing point can be seen much sooner in a darkened area.

What is refractive index?

Refractive Index

Measure of the slowing down and bending of light rays as they enter a gemstone. May be used to identify individual gem species.

What is an organic gem?

Organic Gem

Gem made by or derived from living organisms.

What is granite?


Coarse grained igneous rock comprising mainly quartz, feldspar, and mica.

What are igneous rocks?

Igneous Rocks

Rocks formed from eurpted volcanic lava or solidified magma.

What are metamorphic rocks?

Metamorphic Rocks

Rocks that have been changed by heat and/or pressure to form new rocks consisting of new minerals.

What is mineral?


Inorganic, naturally occuring materials with a constant chemical composition and regular internal atomic structure.

What is cleavage?


Breaking, or tendency to break, of a stone along lines of weakness related to the internal atomic structure.

What is asbestos?


A natural rock fiber that is flame-resistant. It has been used to make insulation, protective gloves, solder pads, flask liners, etc.

What is multicolored?


Used to describe single crystals made of different colored parts.

What is a basal pinacoid?

Basal Pinacoid

Feature relating to crystal symmetry. A columnar or prismatic crystal with flat ends may be referred to as having a basal pinacoid.

What is polycrystalline?


Refers to a mineral made of many small crystals.

What does columnar mean?


Type of habit in which crystals form in the shape of columns.

What is chatoyancy?


The cat's eye effect shown by some stones when cut en cabochon.

What is heat treatment?

Heat Treatment

Application of heat to a gem with the purpose of enhancing the color or clarity.

What are faces?


Flat surfaces that make up the external shape of a crystal.

What is cut?


Term used to describe the way in which a stone is faceted.

What is a bezel?


A metal collar fitting around a stone to secure it into the jewelry piece.

What is lava?


Molten rock erupted from volcanoes.

What is dispersion?


The splitting of white light into its constituent spectral colors - the rainbow of colors - when it passes through inclined surfaces, such as those on a prism or faceted gem. Dispersion in a gem is called fire.

What is a binding wire?

Binding Wire

Soft iron used to hold joints and pieces of metal in the desired position while being soldered.

What does dichroic mean?


Refers to a gem that appears two different colors or shades when viewed from different directions.

What is crystal structure?

Crystal Structure

The internal atomic structure of a crystal. All crystalline gems may be classified in one of seven groups according to the symmetry of their structure: cubic, tetragonal, hexagonal, trigonal, orthorhombic, monoclinic, and triclinic.

What is a girdle?


Band around the widest part of a cut stone where the crown meets the pavilion.

What is asterism?


Star effect seen on some stones when cut en cabochon.

What is a damascus steel?

Damascus Steel

Pattern welded, laminated steel originally popularized in Damascus. Today's process is a modification of the original technique.

What is specific gravity?

Specific Gravity (sg)

Density, measured as the weight of the material, compared with that of an equal volume of water.

What is schist?


Metamorphic rock in which the crystals are in parallel arrangements.

What is rough?


Term used to describe a rock or crystal still in its natural state, before faceting or polishing.

What is massive?


Used to describe minerals that have an indefinite shape or that consist of small crystals in masses.

What is a gemstone?


Decorative material, usually a mineral, prized for some or all of the qualities of beauty, durability, and rarity. It is used synonymously with gem, stone and jewel.

What is a cameo?


Design in low relief, around which the background has been cut away. The result is a design that protrudes from the base of the stone.

What does botryoidal mean?


Shape similar to a bunch of grapes. An example of this habit is malachite.

What is ductility?


A metal's capacity to be drawn into wire. A good indicator of a metal's ability to stretch.

What is a crucible?


A ceramic or graphite container in which metal is melted.

What is a burr?


A rotary steel cutting tool used in a flexible shaft machine.

What is pegmatite?


An igneous rock formed as residual liquids from magma cool, often forming large crystals.

What is mammillated?


Smooth rounded shape.

Who is a lapidary?


Craftsman who cuts and polishes gemstones.

What is a facet?


Surface of a cut and polished gem.

What is the crown of a stone?


The angled facets on a gem just above the girdle.

What is a rhomb?


A shape much like a skewed cube.

What is platy?


Habit characterized by flat, thin, platelike crystals.

What is a crystal?


A solid that has a definite internal atomis structure, producing a characteristic external shape and physical and optical properties.

What is an anvil?


Usually a heavy supporting surface over which metal is hammered. Anvils have a traditional form composed of a squarish base, flat face, and tapered horn.

What is a carat?

Carat (ct)

Unit of weight for gems. A carat is one fifth of a gram.

What is an absorption spectrum?

Absorption Spectrum

Pattern of dark lines or bands seen when a gem is viewed through a spectroscope.

What is diffraction?


The splitting of white light into its constituent spectral colors - the colors of the rainbow - when it passes through a hole or grating.

What is matrix?


The rock in which a gem is found. Also known as host rock or parent rock.

What is iridescence?


Reflection of light off internal features in a gem, giving rise to a rainbow like play of colors.

What is idiochromatic?


Describes gems whose color is due to elements that are an essential part of their chemical composition.

What is pleochroic?


Term used to describe a gem that appears two or more different colors or shades when viewed from different directions.

What is a mixed cut?

Mixed Cut

Cut in which the facets above and below the girdle are styled in a different way. These are usually brilliant cut above and step cut below.

What is karat?

Karat (kt)

A unit of measure to denote the purity of gold.

What is chatoyance?


A fibrous, satin like sheen appearing on the surface of some polished stones.

What is anodizing?


The electrochemical application of an oxide film layer over aluminum causing its surface to become harder, abrasion and corrosion resistant, and chemically color absorbent.

What is double refraction?

Double Refraction

Phenomenon in which each ray of light is split in two as it enters a noncubic mineral. Each ray travels at a different speed and has its own refractive index.

What is ore?


Rock that contains metals capable of being extracted commercially.

What is microcrystalline?


Mineral structure in which crystals are too small to be detected by the naked eye.

What does vitreous mean?


Glasslike luster.

What is a casting?


The pouring or introduction of a molten material into a mold.

What is a table facet?

Table Facet

The central and top facet on a gem.

What is magma?


Rock in a molten state below the earth's surface.

What is an evaporite deposit?

Evaporite Deposit

Sedimentary rock or mineral resulting from the evaporation of water from mineral-bearing fluids, usually seawater.

What is rock?


Material made up of one or more minerals.

What are associated minerals?

Associated Minerals

Minerals found growing together, though not necessarily intergrown.

What is pseudomorph?


One mineral occuring in the crystal shape of another.

What is a step cut?

Step Cut

Cut characterized by a rectangular table facet and girdle, with rectangular facets parallel to these.

What is burnishing?


Smoothing and polishing of metal but rubbing with a hardened steel or stone burnisher.

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