Glossary of Colored Stones

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What is a group?
Family of gems from several closely related mineral species
What is an atom?
The basic structural unit of all matter.
What is a chemical element?
A substance that consists of atoms of only one kind.
What is a chemical composition?
Kinds and relative quantities of atoms that make up a material.
What is a mineral?
A natural, inorganic substance with a characteristic chemical composition and usually characteristic crystal structure.
What is amorphous?
Lacking a regular crystal structure.
Which is an organic gem?
A substance that consists of atoms of only one kind is a
unit cell
gem species
chemical element
Chemical element
What is a rock?
A natural material that's made up of a mass of one or more kinds of mineral crystals.
Where do the world's finest rubies come from?
Mogok, Myanmar region
When were tanzanite's extremely expensive?
What is a gem?
A mineral that is beautiful, durable and rare.
What is the number one colored stone imported into the US?
What group does almandite belong to?
What is a gem variety?
A subcategory of species based on color, transparency or phenomenon.
The US market for natural, unset, non-diamond gems is?
less than a tenth of the size of the diamond market.
Most gems form in the:
oceanic crust
continental crust
Continental crust
Metamorphic rocks?
Altered by heat and pressure.
What gem can crystallize in volcanic rock from gases released by magma?
REd beryl
What is a key locality for hydrothermal gems?
Ouro Preto, Brazil.
What gems form by metamorphism?
Heat and pressure transform limestone into?
A deposit where gems are found in the rock that carried them to the earth's surface?
Which type of deposit is usually the most profitable for colored stones?
Which is a deposit where gems eroded from the source rock and remained in place nearby?
Which is a workable alluvial deposit of gem minerals with economic potential?
Kunzite is most often found in association with?
Tourmaline and beryl in pegmatite.
Myanmar's famous Mogok ruby deposits were formed by
Regional metamorphism
Pegmatite gems are rich in volatile elements like?
Beryllium, boron, and lithium
MOst of the gems in Tanzania's Umba river valley are found in?
Placer deposits.
Emeralds are rarely found in placer deposits because they're?
Unable to withstand much abrasion.
What is igneous rock?
Rock formed by the crystalliztion of molten material.
What is sedimentary rock?
Rock produced from the eroded and weathered remains of existing rock.
Name some igneous rocks:
Red Beryl
Name some metamorphic rocks:
What is a pegmatite?
An igneous rock formed from cooling once molten granite that follows fractures in its surrounding rock.
What is hydrothermal fluid?
Mineral rich pressurized hot water
What is formed when acidic copper rich solutions seep through and react with volcanic rock that contains aluminum and phosphorous?
What forms when acidic copper rich solutions seep through and react with volcanic rocks that contain limestone?
The oceanic crust is made of?
What is an eluvial deposit?
A deposit where gems are eroded from the source rock but remain in place close to the source.
What is an alluvial deposit?
A deposit where gems are eroded from their source rock, then transported away from the source and further concentrated.
What is a unit cell?
A unit cell is a minerals "signature"-it's basic identity. It is the smallest group of atoms with both the characteristic chemical composition and crystal structure of a mineral.
What is an aggregate?
A mass of tiny, randomly oriented crystals.
Where does Imperial Topaz come from?
Ouro Preto mine in Brazil. It is a hydrothermal gem.
What is flux?
Flux is a growth medium.
What is microcrystalline?
Crystals visible under magnification.
What is cryptocrystalline?
Only the highest power magnification can detect individual crystal.
What is triclinic?
The least symmetrical structure.
What is isometric?
A cubic crystal system. i.e.diamond and garnet. It has the highest symmetry
What is twinning?
Change in a gem's crystal direction during or after growth.
what is a twinning plane?
Location of a change in crystal growth direction.
What is an inclusion?
A characteristic enclosed within a gemstone or reaching it's surface from the interior.
What is a liquid inclusion?
Small pocket in a gem that's filled with fluids and sometimes gas bubbles and tiny crystal.
What is a two phase inclusion?
A hollow cavity in a gem usually filled with a liquid and a gas.
What is a three phase inclusion?
A hollow cavity in a gem filled with a liquid, a gas and one or more crystals.
What is a trace element?
Atoms in a gem that aren't part of its essential chemical composition.
What is a habit?
The characteristic external crystal shape or form of a mineral.
What is anhedral?
Crystals without obvious crystal faces.
What is density?
How heavy an object is in relation to its size.
What is specific gravity?
Ratio of the weight of a material to the weight of an equal volume of water.
What is durability?
A gemstone's ability to withstand wear, heat and chemicals.
What is hardness?
How well a gemstone resists scratches.
What is toughness?
How well a gemstone resists breaking and chipping.
What is cleavage?
A smooth, flat break in a gemstone parallel to planes of atomic weakness, caused by weak or fewer bonds between atoms or both.
What is parting?
A flat break in a gemstone caused by concentrated included minerals parallel to a twinning plane.
What is a fracture?
Any break in a gem other than cleavage or parting.
What is a conchoidal fracture?
A curved and ridged fracture in a gemstone extending from the surface inward.
What is stability?
How well a gemstone resists light, heat and chemicals.
What is thermal shock?
Damage caused by sudden extreme temperature changes.
What is cyclic twinning?
when the twinning planes aren't parallel and it results in a wheel shaped crystal.
What is penetration twinning?
When twinned crystals looks as though two crystals have grown through one another.
What is polysynthetic or lamellar twinning?
Crystals that might start out untwinned, but become twinned when the rocks they formed in are altered by pressure during metamorphism.
What is selective absorption?
The light you see-the color of the gem-represents the light that was returned to your eye without being absorbed.
What is absorption spectrum?
A pattern of dark lines or bands shown by certain colored gems when viewed through a spectroscope.
What is allochromatic?
A gem colored by trace elements in its crytal structure.
What is idiochromatic?
A gem colored by an element that is an essential part of its chemical composition.
What are transition elements?
Elements that can selectively absorb some wave lengths of visible light and produce color in gems.
What is vanadium?
A trace element that can produce brilliant greens
What transition element causes the most different gem colors?
What is florescence?
Emission of visible light by a material when it's stimulated by ultraviolet radiation.i.e. rubies display fluorescence.
What is charge transfer?
A process where the electrons that selectively absorb light are passed back and forth between neighboring impurity ions.
What is intervalence charge transfer?
A process where two impurity atoms separated by another atom can still exchange electrons to selectively absorb light.
What is a color center?
A small defect in the atomic structure of a material that can absorb light and cause rise to a color.
What is refraction?
The change in direction and speed of light as it travels from one material to another.
What is double refraction?
When a gems crystal structure splits light into two rays that each travel at a slightly different speed and direction.
What is an optic axis?
Direction of single refraction in a doubly refractive gen. i.e. zircon
What is pleochroism?
When a gem shows different bodycolors from different crystal directions.
What is phenomenon?
An unusual optic effect displayed by a gem.
What is interference?
Interaction of two light rays traveling in the same path.
What is play of color?
The flashing rainbow colors in opal.
What is diffraction?
A special kind of interference phenomenon that breaks up white light into its spectral hues.
What is labradorescence?
A broad flash of color in labradorite feldspar that disappears when the gem is moved.
What is iridescence?
a rainbow effect created when light is broken up into spectral hues by thin layers.
What is Orient?
Iridescence seen in some natural and cultured pearls and mother of pearl.
What is adularescence?
the cloudy bluish white light in a moonstone caused by scattering of light.
What is chatoyancy?
Bands of light in certain gems, caused by reflection of light from many parallel, needle-like inclusions or hollow tubes.
What is milk and honey?
A two-toned effect seen when a chatoyant gem is positioned at right angles to a light source.
What is asterism?
Crossing of chatoyant bands, creating a star in the dome of a cabochon.
What is aventurescence?
A glittery effect caused by light relecting from small flat inclusions within a gemstone.
what is color change?
A distinct change in gem color under different types of lighting.
What is melt process?
A synthetic crystal growth method in which the chemical mixture is melted, then recrystallized.
i.e.flame fusion, pulling
What is a solution process?
A synthetic growth method in which the crystal grows from a dissolved chemical mixture, sometimes at high temperature and pressure.
what is flame fusion?
A process in which powdered chemicals are dropped through a high temperature flame onto a rotating pedestal to produce a synthetic crystal.
What is pulling?
A process in which the synthetic crystal grows from a seed that is dipped into a chemical melt, then pulled away as it gathers material.
What is a seed crystal?
A tiny crystal used as a template to control the size speed or direction of growth and the shape of a growing synthetic crystal.
What is a floating zone?
A melt process where a heating unit passes over a rotating solid rod of chemicals until it forms a synthetic crystal.Used by Seiko in 1980's
What is skull melt?
A synthetic crystal growth method that uses colling pipes around an interior of melted chemical ingredients.
What is flux growth?
A process in which nutrients dissolve in chemicals to form synthetic crystals.
Used for quartz and emerald.This solution method is high cost, low volumn.
What is hydrothermal growth?
A process in which nutrients dissolve in an acidic water solution at high temperature and pressure to form synthetic crystal.Imitates conditions deep in the earth that result in the formation of natural crystal.
What is spontaneous nucleation?
A synthetic crystal growth method that starts without a seed crystal.
What is a ceramic process?
A process in which finely ground powder is heated, sometimes under pressure to produce a fine grained solid material.
What is a doublet?
Two separate pieces of material fused or cemented together to form a single assembled stone.
What is a treatment?
Any human-controlled process beyond cutting and polishing, that improves the appearance, durability or value of a gem.
What is fracture filling?
Using a filler to conceal fractures and improve the apparent clarity of a gem.
What is disclosure?
Clearly and accurately informing people about the nature of the goods they buy.
What is a heat treatment?
Exposing a gem to rising temperatures for the purpose of changing its appearance
What gems are commonly heat treated?
What is an oxidizing environment?
An oxygen-rich environment that surrounds a gem during heat treatment, causing it to absorb oxygen.
What is a reducing environment?
An oxygen-poor environment that surrounds a gem during heat treatment, causing it to lose oxygen.
What is quench crackling?
A rapid heating and cooling process that produces fractures in a stone so it will accept dye.
What is surface diffusion?
A treatment in which a gem is exposed to high temperatures and chemicals to allow color-causing elements to penetrate its surface.
How deep is the layer of surface diffusion?
The layer is only 0.01mm to 0.50 mm deep.
What is resin?
Resin is a clear, viscous substance that's used to fill fractures in gemstones.
What is polymer?
A liquid filling material that's very durable when it dries.
What is a hardener?
A chemical that treaters mix with some resins to cause them to harden.
What is irradiation?
Exposing a gem to radiation to change or improve its color.
What are some commonly irradiated gems?
cultured pearls
What is bleaching?
A treatment that uses chemicals to lighten or remove color.
What is colorless impregnation?
Filling of pores or other openings with melted wax, resin, polymer, or plastic to improve appearance and stability.
What is the Zachary method?
Atreatment used on turquoise in the late 1980's to give the turquoise better color, less porosity and the ability to take a better polish.
What is dyeing?
A treatment that adds color or affects color by deepening it, making it more even, or changing it.
What gem is often treated with a combination of bleaching and impregnation?
What are some commonly dyed gems?
What is surface modification?
Altering a gem's appearance by applying backings, coatings, or coloring agents like paint.
What is a sugar treatment?
Soaking an opal in a hot sugar solution and then in sulfuric acid to darken it and bring out its play-of-color.
What is a smoke treatment?
Heating a wrapped opal until smoke or ash penetrates its surface to darken it and bring out its play-of-color.
What is aqua aura?
It is an iridescent blue-green color that comes from an extremely thin coating of gold. It is commonly used on colorless or near-colorless quartz and topaz.
What is a source?
A gem-producing area, or a particular mine in that area.
Where are the finest rubies from?
The Mogok area of Thailand.
What is a mine lot?
A mixture of gem qualities that represents unsorted production from a particular mine.
What is a grade?
A specific rough gemstone quality range, usually determined by color, size, clarity, and price.
What is a facet grade?
Gemstone rough that's transparent enough and of high enough quality to produce faceted gems.
What region do most mass market rubies come from?
Mong Hsu
What is high grading?
In mining terms, theft of a mine's production by its workers.
What is a parcel?
A quantity of stones sometimes of similar size and quality, perhaps from a single mine, but often from various sources, that's offered for sale together.
What is the origin?
The geographical place where a gem was mined.
What is a cutting center?
A city, region or country with a laarge number of gemstone maufacturers.
What is a cutter?
A manufacturer who produces faceted stone, cabochons, or carvings.
What is free-size?
Non-standard cutting, usually applied to large, important stones for use in expensive jewelry where standard size is not a consideration.
What are calibrated sizes?
Gemstones sizes cut to fit standard mountings.
What is the commercial market?
Market sector where average-quality gemstones are used in mass market jewelry.
What is the middle market?
Market sector where better-quality gemstones are used in well-finished, moderately price jewerlry pieces.
What is the high-end market?
Market sector where fine-quality, expensive gemstones are used in unique, handcrafted jewelry pieces.
What is a "cut"?
A gem dealer's term for a random sample from a parcel of gemstones often used to assess the parcels overall quality.
What is a lot price?
A price for buying the entire parcel, or a substantial part of it.
What is the pick price?
A premium price for selecting stones from a parcel.
What is hue?
The first impression of an object's basic color.
What is tone?
Degree of darkness or lightness of a color.
What is saturation?
A colors strength or intensity.
What is bodycolor?
A gemstone's basic color, determined by the gem's selective absorption of light.
What is extinction?
Unattractive dark areas in a faceted transparent colored stone.
What is color zoning?
Areas of different color in a gem, caused by variation in growth conditions.
What is a preform?
Rough ground to the approx shape of the finished stone.
What is a dopstick?
Wooden or metal stick that holds the preform during faceting.
What is a lap?
Horizontal spinning metal disk used to grind or polish a gem's facets.
What is a cameo?
A gem carving style in which the design, often a woman's profile, projects slightly from a flat or curved surface.
What is intaglio?
A design engraved into the surface of a gemstone.
What is a fantasy cut?
A free-form cut that can feature alternating curved or flat surfaces.
What are designer cuts?
Artisic gem cuts that aren't limited to specific proportions or shapes.
What are the five factors that determine the influence of clarity characteristics on marketability:
What is a cloud?
Any hazy or milky area that cannot be described as a feather, fingerprint or group of included crystals or needles.
What is a feather?
A general term for a break in a stone.
What is a fingerprint?
Inclusions that form a pattern that often resembles a human fingerprint.
What is silk?
Group of fine, needle-like inclusions that can create phenomena such as cat's eye and stars.
What is a negative crystal?
An angular, hollow space within a gem that resembles a mineral inclusion.
What trace element causes ruby to be red?
The finest rubies usually form in what kind of deposits?
In ancient Sanskrit, ruby is called ratnaraj or?
king of precious stones.
The most valuable tone and saturation for ruby are?
medium to medium dark tone and vivid saturation.
Rubies that come from marble deposits are typically low in?
Rubies deposits in Thailand, Cambodia, and Madagascar are associated with
The world's largest corundum marketing center is ?
In the 1980's, the major source of rubies was?
What rubies are the finest-quality stones regardless of origin?
Burmese rubies.
What are "Thai" or "Pailin" rubies?
Rubies that come from an area between Thailand and Cambodia. They are generally brownish red to purplish red hue and have a meium-dark to dark tone.
What are "Sri Lankan" rubies?
Rubies that range from purplish red to pinkish red and are medium to very light in tone.They tend to look like pink sapphires.
What is a common sapphire characteristic?
Color zoning
What is geuda?
A milky grayish or brownish corundum that can be treated to a fine blue color.
What is Dhun?
a smoky corundum that turns blue when treated.
Where are sapphires found?
Southeast Asia, Australia, and Africa.
What are the most coveted colors of star corundum?
Rich reds and vivid blues of faceted rubies and sapphires.
What is the most valued star corundum?
Star ruby.
Where are 90% of the star rubies and star sapphires found?
In alluvial deposits in Sri Lanka.
What causes most fancy sapphire colors?
Trace elements of iron, titanium and chromium.
What causes sapphire's color change?
When were the first flame-fusion star rubies produced?
What is a major source of black sapphire?
Which color of star sapphire is usually cut shallow due to parting?
What color sapphire is readily available, but its color isn't very marketable?
What do iolite, chrysberyl,andalusite and tanzanite have in common?
They are all pleochroic.
Where is tanzanite mined?
Merelani, an area of northern Tanzania in eastern Africa.
Who named Tanzanite?
Tiffany& Co.
What is the best tanzanite color?
Strongly saturated pure blue or violetish blue.
Most Tanzanite is heat treated from what color?
What is the most convincing tanzanite imitation to date?
Synthetic fosterite.
What is thulite?
A translucent to opaque pink zoisite streaked or mottled with gray or white.
What is Purple Coranite?
It is the trade name for a purple synthetic yttrium aluminum garnet.(YAG)
What is iolite's most dominant feature?
It's pleochroism
Is iolite treated?
Where is iolite primarily from?
Sri Lanka.
What are the 2 most rare and desirable gems on earth?
Alexandrite and cat's eye chrsoberyl.
Where was alexandrite discovered?
The Ural mountains of Russia in 1830.
What is alexandrite's defining characteristic?
It's color change
What is "the alexandrite effect"?
The color change phenomenon.
What color is alexandrite in the day?
Saturated bluish green through yellowish green.
What color is alexandrite by night?
orangy red through purple-red with meium to medium dark tone and moderately strong saturation.
Where was alexandrite discovered in 1980's to increase availability?
What synthetic is often used to imitate natural alexandrite?
Synthetic spinel and synthetic corundum with color change.
What is cymophane?
A Greek name for cat's eye chrsoberyl.
What is the most prized chatoyant gemstone?
Cat's eye chrysoberyl.
Where are the finest deposits of cats eye chrysoberyl?
Sri Lanka.
Where is andalusite from?
What are the most prized colors of andalusite?
Yellowish green and orange.
What is chiastolite?
Opaque material with a distinctive cross-shaped marking.
What is the finest color of lapis?
Violetish blue, med to dark in tone, and highly saturated. No visible calcite.
In order of value, what grades of lapis or on the market today?
Persian or Afghan-Intense, uniform, med-dark blue
Russian or Siberian- various intensities of blue
Chilean- often tinted with green
What produces lapis lazuli's prized color?
What is the world's major source of lapis?
What is asmani?
Mid-quality light blue lapis marketed as denim lapis.
what is Gilson?
Imitation lapis. It has a hardness of 3 and its luster is dull.
What is turquoise's most prized color?
An intense, uniform, medium blue.
What causes the bluer shades of turquoise?
Where do turquoise deposits form?
Limonite or Sandstone
What causes turquoise to appear greenish blue?
What is spiderweb turquoise?
turquoise that contains matrix in thin, delicate, web-like patterns across the face of the gemstone.
What is stabilized turqoise?
Polymer-impregnated turquoise.
Who is the largest producer of turquoise?
Southwest US
Where does the top color turquoise come from?
China's Hubai province
What is reconstructed turqoise?
A turquoise imitation made of a mixture of powdered minerals, dyed and bonded with plastic or epozy resin.
What is chrysocolla chalcedony?
A blue variety of chalcedony which resembles turquoise. It is translucent to semitranslucent. It is an intense light blue to blue-green.
Where does sugilite get its red-purple to bluish purple hue?
What is blue john?
A bluish violet to purple fluorite with curved or angular bands.
Where is the sole source for charoite?
What is the material know as marcasite in today's jewelry?

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