Glossary of Terms

~ A ~

Agate ~ Multi-coloured microscopically crystalline, variegated chalcedony. It may be banded, irregularly clouded or have visible impurities as in moss agate. It is a very common variety of quartz principally found in Brazil

Alexandrite ~ A variety of chrysoberyl which changes colour in different lights due to its unusual absorption. Green in daylight and wine-red in most artificial lights, but the colour changes will vary in different stones. It was originally found in the Ural Mountains and named in honour of Alexander II of Russia. It has since been found in Ceylon, Brazil and Tanzania.

Alloy ~ 1. A Metal that is to be melted with another to form a compound metal with qualities suitable for some particular use.  2. The resulting compound metal from melting two or more metals together, whose properties may differ from those of its components.

Aluminum Oxide ~ A hard abrasive available in various grades and grain sizes.

Amber ~ Fossilized resin. It is the preserved gum of coniferous trees. Often insects which were entrapped in the gum when it was exuded are seen preserved within the stone.

Amethyst ~ An ornament of gold, silver or other material worn around the ankle in the same manner as a bracelet is on the wrist.

Anklet ~ An ornament of gold, silver or other material worn around the ankle in the same manner as a bracelet is on the wrist.

Annealing ~ The toughening or softening of metal by heating, making it more malleable.

Anniversary Band ~ See eternity band

Anode ~ The term in electroplating for the positive pole in the plating bath. A piece of metal (also called an anode) is attached to the anode. Metal from this anode is electro-deposited onto the item being plated (cathode).

Anti-flux ~ A chemical which retards the flow of melted solders.

Anvil ~ A fixed, solid base which may be struck.

Aqua Regia ~ A mixture of nitric acid and hydrochloric acid, used for testing high karat golds by the touchstone (stone and needle) method. Also used to dissolve gold and platinum. An average proportion is three parts hydrochloric acid to one part nitric acid. Care must be taken in mixing acids, and not to breathe the chlorine that is created. It was named aqua regia by medieval alchemists because it would attack the royal metals, platinum and gold.

Aquamarine ~ Sky-blue to greenish blue gem stone.

Arbor ~ A part of a mechanism that rotates or that turns in pivot bearings while holding something that turns. An example would be the mini mandrels when in a flexshaft handpiece.

Arkansas Stone ~ A grayish-white stone used primarily for preparing gravers and pivots for polishing.

Assaying ~ Testing alloys, bullion and ores to determine the proportions of precious metal content.


~ B ~

B & S Gauge ~ Standard American gauge used to measure the thickness of wire and sheet.

Baguette ~ 1. A rectangular shaped small diamond or gemstone.  2. A very small rectangular bracelet watch.

Bail ~ A loop of sheet metal or heavy wire attached to a pendant, used as the hanging device to connect the pendant to a necklace.

Band ~ 1. A wedding ring.  2. A watch strap or bracelet.

Bangle ~ A solid or hollow, non-flexible bracelet. A wire bracelet.

Barrette File ~ A file with teeth cut on the lower side, its back uncut with a ridge. Also known as a safety back file.

Bastard File ~ A rough, coarse cut file.

Battery Strap ~ A metallic piece used to secure the battery to the watch movement.

Beading ~ A style of gemstone setting where the prongs are formed over the edge of the stone by pressing metal (usually with a graver) into a “bead.”

Beeswax ~ Wax produced in beehives used as a lubricant for wire-drawing, sawing, drilling, and bead stringing.

Bezel ~ 1. The upper part of a gem, the crown facets, namely those above the girdle.  2. A continuous groove of a form to fit a stone in a piece of jewellery, with metal at the top of the groove burnished over the edge of the stone to form a setting.  3. The grooved ring forming part of a watch case around the dial into which the watch crystal is fitted.  4. A metal ring fitted around a coin or token allowing the piece to be worn as a pendant.

Birefringence ~ A technical term for the separation by a doubly refracting crystal of a single light ray into two rays moving at different speeds. If the difference is too small to be seen with the eye, a dichroscope may be used.

Black Chrome ~ A black chromium finish applied to gold by electroplating.

Black Onyx ~ Almost unknown in nature, it is produced by warming chalcedony in a sugar solution for several days or weeks. The stone in then placed in warm sulphuric acid. The acid reacts with the sugar, precipitating the free carbon. The colour is permanent.

Bobbing Compound ~ A tripoli-like compound that is used as an abrasive before polishing.

Boley Gauge ~ A Vernier slide gauge of light construction convenient for use by watchmakers and jewellers

Borax ~ A chemical substance used as a flux in soldering precious metals. Borax is dissolved in water and applied to the joint and pieces of the solder before heat is applied to melt the solder.

Bow Opening Pliers ~ Pliers with a long nose whose ends open when the plier is squeezed. Used to spread open bow pendants, bails, jump rings, etc.

Brass ~ An alloy composed of various proportions of brass and zinc. A common formula is 65% copper, 35% zinc.

Brazing ~ Welding with brass alloy rods.

Bright Finish ~ The finish that imparts to silver or gold a highly polished, mirror-like surface.

Brilliance ~ When used in reference to a gem, it refers to the brightness of the stone, which is related to the surface polish and the internal reflection of light from the back facets.

Brittleness ~ The tendency for a metal to crack or break with deformation.

Broach ~ A tool used for enlarging or finishing holes. Cutting broaches have faces on them lengthwise and slightly tapered. Polishing broaches have no cutting edges but the round surface is slightly scored lengthwise.

Bronze ~ 1. A reddish-brown alloy of copper and tine.  2. An artistic reproduction in bronze as a stature for example.

Bronzing ~ Painting with metallic powder mixed with a transparent varnish. A cheap process used where electroplating is inadvisable.

Brooch ~ A piece of jewellery that is worn pinned to clothing at the neck, shoulder, breast or hat. Can also be worn in the hair.

Buff ~ A piece of quilted material (felt, muslin, leather, etc) used with abrasive materials. Buffs are both circular for used on polishing machines and flat for use by hand.

Bullion ~ Gold or silver in bar, ingot or other form, as distinguished from coins.

Burn Out ~ The elimination of wax from a mould in a furnace or kiln.

Burnisher ~ A tool for polishing metal.

Burnishing ~ To produce a polished surface on metal by rubbing it with a hard, smooth, highly polished steel tool. No metal is removed.

Burnout Furnace ~ An electric or gas powered oven used to eliminate, by burning out, the wax from investment moulds.

Butt Joint ~ The joining of two sheets of metal edge to edge in the same plane.


~ C ~

Cable ~ String or cord of twisted material typically metal wire when referring to jewellery.

Cabochon ~ An unfaceted form of cutting generally used on opaque and translucent stones. The stone is given a rounded, convex shape.

Cadmium ~ A metal that is used as an alloy in solders to promote easy flowing under heat.

Cameo ~ A stone, usually composed of two different coloured layers, which has been carved so that a raised image in one colour stands on a background of the other colour. Cameos are principally cut from a variety of agate. Shells are another common material.

Carat ~ A unit of weight for gemstones. Now generally accepted as one-fifth of a gram (200 milligrams).

Casting ~ The process of forming an object by pouring melted metal into a hollow mould. This process in often used to duplicate a piece of jewellery by using the original piece as a pattern for making the mould. Today most casting processes involve forcing molten metal into an investment mould from which a wax pattern has been burned out. Centrifugal or vacuum casting machines are the most common units used.

Cathode ~ The negative pole in an electric circuit. In an electroplating bath, the object being plated is the cathode.

Center Punch ~ A steel punch that has a v-shaped tip used to mark a point on metal and for starting a hole for drilling. An automatic centre punch is spring loaded thus marking the metal without the use of a hammer or mallet.

Centrifugal Casting ~ A method of casting metal where metal is forced in a mould by the centrifugal force of a spinning machine. The force “packs” the metal into the smallest spaces producing sharp detail. Synonymous with lost wax casting.

Channel Setting ~ A type of stone setting often used in mounting a number of small stones of uniform size in a row as in a diamond wedding ring. Instead of each stone being held by its individual set of prongs, the stones are fitted into the channel and held into place on each side by a continuous strip of metal.

Chasing ~ A method of surface decoration in sheet metal without removing any metal. The design is created with a hammer and punches that are worked over the front of the metal. The result is a low relief embossed into the sheet.

Chatham-Created Emeralds ~ The term given to synthetic emeralds made by Carroll F. Chatham. They were approved by the Federal Trade Commission in 1963. The FTC found that the term imputes “that this product is not a creation of nature, that is man-made, and that it is artificial or synthetic.”

Chinese White ~ An oxide of zinc used in a cake or paste form. It is used to coat gold and silver with a white substance on which jewellers and engravers can draw a design that they will engrave.

Chip ~ Common term for a small, single cut diamond

Choker ~ A short necklace usually 14″, just long enough to go around the neck. Often applies to a string of pearls or beads.

Chuck ~ A work holding device used in lathes consisting of a steel cylindrical piece with slits radiating from a hole to form a spring-jaws to clamp the work.

Citrine ~ A yellow to brownish variety of quartz. Almost all “so-called” topaz in the trade is actually citrine quartz. In those cases the use of the word topaz, without the word quartz, constitutes unfair trade practices.

Clasp ~ The fastener used to connect the ends of a necklace, bracelet, or other such piece of jewellery. Clasps take on a great variety of forms such as lobster claws, spring rings, box catches, etc. Fine pieces of jewellery may have decorated clasps or clasps set with gemstones.

Class Ring ~ A ring bearing a school insignia and date of graduation.

Coddington Magnifier ~ An optical lens used for inspecting diamonds and other gemstones. It is usually mounted in a loupe casing and comes in strengths ranging from 7x to 20x.

Coin Gold ~ United States gold coins were made of an alloy consisting of 9 parts pure gold and 1 part copper.

Crocus ~ An abrasive material consisting of coarse grains of iron oxide that is used for grinding metal before polishing. Finer grains are called rouge.

Crucible ~ A vessel made of a refractory material such as silica or carbon in which metals are melted. They are available in varying shapes and sizes for different purposes.


~ D ~

Dapping Die ~ A cube made of iron and steel with various hemispherical indentations on its faces that are used with corresponding punches to make cup shaped forms in metal sheet.

Dewaxer ~ A device that eliminates a large amount of wax from the investment mould before burnout. The dewaxer uses steam to melt out the wax. This increases burnout efficiency, eliminates much of the burnout fumes, and allows those so inclined to reuse the steamed out wax.

Diamond Bur ~ An abrasive wheel, bur, or drill with embedded diamond particles mounted on a metal form. They are used to drill and grind hard substances.

Diamond Tweezers ~ Tweezers that have rounded points, corrugated tips, and a somewhat weak spring used to grip diamonds and other gemstones.

Dichroism ~ The property possessed by a stone of transmitting (or absorbing) different colours of light in different directions through the crystal.

Dichroscope ~ An instrument consisting of a calcite rhomb (crystal), used to detect dichroism in gemstones.

Die Casting ~ The method of casting in a metal mould.

Die Forming ~ The act of forcing sheet metal into a die.

Die Striking ~ A die struck object is created by striking gold sheet or tubing on one or two dies. The gold is forced, under tremendous pressure, into every crevice of the die with sharp, high detail. The metal is compressed, strengthened, and hardened. It takes on a high polish, is easier to solder, and weighs more than an identical piece made of cast gold because the molecules are squeezed tightly together.

Divider ~ A tool for drawing circles, or spacing units of length. It is made up of two arms joined at a pivot. The tips are hard enough to mark soft metal such as gold and silver.

Draw Plate ~ A steel plate with a series of graduate holes through which softer metals are pulled or drawn to form wire with a diameter of the hole. Some draw plates have tungsten-carbide inserts in the holes for more durability and a long life for the plate.

Drawing ~ Pulling a rod or thick wire through a series of conically shaped holes, progressively smaller in size, to reshape or narrow its width.

Drill ~ A boring tool used to make holes. The twist drill is the most common type in jewelry work, so named for the spiral of “twist” pattern of the cutting edge.

Ductility ~ The ability for a metal to be drawn into wire.


~ E ~

Ear Nut ~ First referred to the tapped earring back used with threaded earring posts, but now refers to any earring back whether for threaded posts or friction posts.

Electroforming ~ A process developed by J. S. Electro-Plating Co., Ltd. of London in the 1960’s. A negative mould that is fitted with electrical contacts is placed into a specially prepared gold or silver bath. Metal builds up on the inside of the mold to any desired thickness, preserving the detail. Another method of electroforming involves coating an object such as a leaf, insect, etc. with a conductive coating and allowing metal to build up on the outside while in the bath. The object on the inside is then dissolved.

Electroplating ~ The process of covering a metal article with a film of another metal. The item is immersed in a chemical solution, a direct electric current is passed through the solution from a piece of metal (anode) to the item to be plated (cathode), and metal from the chemical solution is deposited on the item by electrolysis.

Electrum ~ An alloy that is 20% gold and 80% silver.

Emerald ~ A variety of beryl with a green colour caused by chromium or vanadium. There are some foreign gemmologists that will only call a stone an emerald if the stone is coloured by chromium.

Emery ~ A common abrasive material that consists of a naturally occurring mixture of corundum and magnetite, the magnetic oxide of iron.

Emery Paper Or Cloth ~ Stiff paper or cloth that have various grades of emery glued on its surface. It is used for grinding and polishing. They can be held by hand or wrapped around sticks or dowels. Grits vary from 4/0 or 0000 for the finest to 4 which is the coarsest. NEVER fold your emery paper on itself grit-to-grit. This will just wear away the paper you are not using at the time.

Etching ~ The chemical removal of metal usually with an acid or a chloride.

Eternity Ring Or Band ~ Sometimes called an anniversary band. A narrow band usually of gold or platinum with a set of stones (diamonds or coloured gems) encircling the band (or almost nearly). Usually given by a husband to a wife as a token of continued love to mark an event such as an anniversary or the birth of a child. This custom began in England in the 1930’s and spread to America in the 1970’s.


~ F ~

Felt Wheel ~ a wheel used for polishing and smoothing that is made of compressed felt to insure uniform shape, texture, and density. Available in hardnesses of soft, medium, hard, rock hard, flint hard, and diamond hard. The harder the felt wheel, the better it maintains its shape.

File ~ A hand tool used to cut and shape metal or wax (two commonly used materials by jewelers). They are usually made of steel with teeth that cover its surface. Files are available in a variety of shapes, sizes, and cuts or coarseness.

File Card ~ A brush with steel bristles for cleaning the teeth of a file. Eliminating material and dirt from the teeth of a file will make it cut better and more uniformly.

Fire Coat ~ See fire scale

Fire Scale ~ The layer of oxidized metal on the surface of gold or silver. It may extend below the surface. Caused by heating an item during soldering.

Flask ~ A metal frame which holds the form for casting and commonly looks like a section of steel pipe.

Flux ~ A substance used to promote fusion by preventing oxidation at the point of soldering, thus enabling the solder to flow. When soldering gold and silver, a solution of borax or “self-pickling flux” is used.

Forging ~ The method of shaping a piece of metal with repeated blows of a hammer.


~ G ~

Graver ~ The steel tool used by a hand engraver to cut a design into metal.

Grinding ~ The removal of metal with a rotating, abrasive charged or stone wheel.


~ H ~

Hallmark ~ Today it refers to the mark placed on a piece of jewellery by the maker.


Hard Platinum ~ See iridium

Hardening ~ The process of heating and working metal to reduce its malleability.


~ I ~

Illusion Setting ~ A setting that has a metal surface that surrounds the stone and that is cut or shaped to appear to be part of the stone, often used to enhance the size of small diamonds.

Imperial Jade ~ A popular name given to the fine quality, translucent, emerald green jadeite.

Ingot ~ A bar or cast block of metal.

Investment ~ A fine-grained, heat resistant plaster used to make molds for casting.

Iridium ~ A hard white metallic element of the platinum group, the most corrosion-resistant and one of the densest elements known. In the massive form it is unaffected by acids, including aqua regia. It has a melting point of 2454C and a specific gravity of 22.5. The chemical symbol is ” Ir “. Its main use is as a hardener for platinum. Platinum/iridium alloy contains 10% iridium and is known as “hard platinum.” The 5% alloy is known as “medium hard platinum.”

Iron Oxide ~ Ferric oxide; iron dust; when pulverized, washed and decanted, it is turned into rouge for polishing metal.


~ K ~

Karat ~ A measure of the fineness of gold. One karat is equal to one part in twenty-four in gold alloy.


~ L ~

Liver Of Sulfur ~ Potassium sulfurated, a chemical used when dissolved in water to oxidize silver and other metals, particularly copper alloys such as gold, to produce varying shades of brown to black, for a finish. To make a liver of sulfur solution, mix 64oz. of water with 12oz. of liver of sulfur. You can optionally add 1/8oz. of ammonia for improved blackening. If ammonia is added, proper ventilation is a must. Be sure to wear rubber gloves and an apron. A warm solution facilitates better results. Also be sure to clean and rinse the item before applying the liver of sulfur solution and rinse thoroughly afterwards.

Lost Wax Casting ~ See centrifugal casting.

Loupe ~ A hand-held magnifying instrument used to view gemstones. The industry standard for loupes is a 10x magnification.


~ M ~

Malleability ~ The capacity of a metal to have its shaped changed without loosing its physical integrity (breaking, tearing, shearing, etc.).

Metallurgy ~ The study of the physical and chemical properties of metals.


~ O ~

Oxide ~ Formed when the molecules of a metal combine with oxygen from the surrounding air. The result is a darkening of the metal.

Oxidizing ~ The process that forms oxides on the surface of metal. This is often done purposefully by applying heat or chemicals to a metal to achieve a desired darkening of metal.

Oxidizing Flame ~ A torch flame that contains an excess of oxygen in proportion to the flammable gas (fuel).


~ P ~

Pave ~ Small stones set as close together as possible on the surface of metal.

Peen ~ A domed or curved striking face of a hammer.

Pickle ~ A mild acidic solution used to remove surface oxidation. Sparex is a common brand name of pickle.

Polariscope ~ A gemmologist’s tool that generates a polarized light field for the viewing of gemstones. Viewing gems through polarized light may be used to distinguish one gem from another.

Prong ~ A narrow piece of metal that is folded over the girdle of a stone to secure it in a setting.

Pumice ~ A light weight, glassy volcanic rock that is crushed into a powder for use in jewelry work for producing non-polished finishes on metal. It should always be used with water for lubrication. It should also be rinsed frequently.


~ Q ~

Quenching ~ The reduction of the temperature of a heated metal by submersion in water.


~ R ~

Raising ~ The process of making a hollow form from a metal sheet by gradually bringing up the sides with the blows of a hammer.

Rectifier ~ A device that changes alternating current to direct current. The main tool required in electroplating (plating machine).

Reducing Flame ~ A torch flame that has an excess of flammable gas (fuel) in proportion to the oxygen.

Refining ~ The process of purifying metal.

Rolling ~ The process of changing the thickness of metal sheet by passing it between hardened steel rollers under great pressure.

Rouge ~ A product of iron oxide, pulverized and graded, used in jewellery work. Darker-coloured, coarser grains are called crocus and are used for grinding. The finer grains are called rouge (French for “red”) and are used for polishing steel and precious metals. Rouge is often mixed with a binder and caked into a bar form for easy application to a buffing wheel.


~ S ~

Shank ~ The part of a ring that surrounds the finger, excluding the decorative top or setting.

Smelting ~ The process of separating metals from non-metallic components or other metals.

Smithing ~ The shaping of metal, particularly sheet, with hammer blows.

Solder ~ A metal alloy with reduced melting and flowing temperatures. It is used to join metals by fusing the surfaces of the metals by capillary action.

Solitaire ~ A ring with a single gemstone as its prominent feature.

Stripping ~ The process of removing a thin layer of metal from a surface. This can be done by immersion in acid or by reverse electroplating.

Sweeps ~ The metal filings and scraps collected after working, almost always mixed with waste materials such as abrasives, polishing compounds, buff fibres, etc.


~ T ~

Tarnish ~ The build up of surface oxidation over a period of time.

Touchstone ~ A black siliceous stone on which a metal is rubbed to make a visible streak of metal. Acid is applied to the streak, and the rate at which the streak disappears or the amount of the streak that is left is used to determine the purity.

Tripoli ~ A porous, decomposed siliceous rock which results from the weathering of chert and siliceous limestone. It is used as an abrasive for preparing jewellery work for polishing. The powdered stone is usually mixed with a binder and moulded into cakes for easy application to buffing wheels.

Troy System ~ a method used to weigh precious metals. The name is derived form Troyes, France where the system was used prior to its introduction to England in the 15th century. The smallest unit is a grain (gn.), the same as in the avoirdupois system.

24 grains = 1 pennyweight

20 pennyweights = 1 troy ounce

12 troy ounces = 1 troy pound

 Tsavorite ~ A transparent, nearly emerald green variety of grossular garnet found in mid Africa particularly Kenya (the Tsavo National Game Preserve). It was named Tsavorite by Tiffany & Co. in 1974. It has a hardness of 7 and a refractive index of 1.744.

Tumbling ~ A method of polishing large quantities of jewelryof certain shapes (no sharp corners) by rotating them in a barrel or vibrating them in a tub. Special polishing agents and abrasives are used. The pieces are polished as they rub against the abrasives or each other.

Tungsten Carbide ~ Carbonized tungsten that is used in a powder form as an abrasive. It can also be formed into a solid form with a binder making a hard substance for tools for cutting metal.

Turquoise ~ A hydrous copper aluminium phosphate that always occurs in fine-grained, compact masses in a light blue colour often with bits of brown or grey. This opaque stone is almost always cabochon cut. It has a hardness of 5 to 6, a refractive index of 1.61 to 1.65, and a specific gravity of 2.6 to 2.9. It is commonly found in the arid south west United States and Mexico.

Tweezer ~ A tool for picking up small items such as watch parts, stones, findings, or small jewellery pieces. It is usually two pieces that are attached at one end that acts as the pivot for the pieces to turn on each other. In this way the tweezer is open unless squeezed closed with the fingers. They can have different jaws or be made of different materials for different uses.


~ V ~

Vermeil ~ Though it has had several meanings throughout its usage, it has generally come to mean heavy gold electroplating over sterling silver.

Vibrator ~ In jewellery casting it is a table that shakes at a significant intensity to cause air bubbles to rise out of an investment slurry before the burnout cycle is begun. Bubbles in the investment slurry can stick to the wax pattern inside and cause a poor finish on a final casting.

Vibrograf ~ The trade name for a watch timing machine.

Vincenza ~ An Italian jewellery-making centre located about 40 miles west of Venice.

Vulcanizer ~ A heated press used to melt layers of rubber in a mould into one solid piece. After the vulcanization process, the rubber mould is cut apart to remove the”original” piece from inside and to create a way for molten wax to enter to make a wax pattern.


~ W ~

Watch Cleaning Machine ~ Composed of a set of jars that contain cleaning and rinsing solutions and with electric-motor driven receptacles for watch parts immersion. The machine usually has a heater for drying parts after rinsing.

Watchmaker ~ The current usage is for anyone who repairs watches. This person presumably is skilled in making or improvising the use of parts for any watch. This term does not describe the person who assembles one part of a watch on an assembly line.

Water Resistant ~ A term allowed by the Federal Trade Commission when a watch has passed a test in which it is immersed in water at normal pressure (15psi) for five minutes and then for an additional 5 minutes at a pressure of 35psi without showing indications of moisture intrusion.

Waterproof ~ A term that is disallowed by the Federal Trade Commission to describe a watch whose case is impervious to moisture.

Wax ~ A generic term used to describe a group of specifically formulated waxes each for a specific purpose such as casting, filing, shaping, etc. Also a colloquial term for a wax pattern.

Wax Injector ~ A device designed to force molten wax into a rubber or metal mold in order to make a wax pattern. Pressure for the wax injector is supplied by compressed air from hydraulic pressure.

Wax Pattern ~ A three dimensional pattern either carved from a block of wax, formed from various wax components, or created by a mould injected with molten wax. The wax pattern is then used to form the casting pattern in lost wax casting.

White Metal ~ A metal that is a mixture of tin, antimony, and copper in various proportions. It is sometimes used as a base for expensive electroplated jewellery.

Wire Gauge ~ A flat plate of metal with holes and slots for graduated sizes used to measure the thickness or gauge of a piece of metal wire or sheet.

Works ~ A colloquial term for the movement of a watch.


~ Y ~

YAG ~ Abbreviation for yttrium aluminium garnet.

Yellow Ochre ~ A yellow, powdery, clay-like material that when mixed with water forms a paint that will inhibit the flow of solder.

Yttrium Aluminium Garnet ~ An incorrect term for the synthetically grown compound of yttria and alumina. It forms cubic crystals similar to spinel. Its internal structure is like that of garnet, but garnet contains silica not alumina. It has also been found to occur naturally. This compound has a refractive index of 1.833, a hardness of 8½, and a specific gravity of 4½.


~ Z ~

Zircon ~ A gemstone characterized by very high refractive indices of 1.93 to 1.99. It has a hardness of about 7½ and a specific gravity of 4.68. The stone has natural colors of yellow, brown, red and green. Heat can create blue, clear and greenish stones. Zircon has high dispersion and a well cut stone has good fire.