Absolute hardness
It is a scale to measure the hardness of a mineral. It is used by scientists as it has its numbers in proportion. Mineral collectors measure hardness using the Mohs scale.

Absorption spectrum
It is the absorbed light in a gem or mineral when bands of light passes through. Different gems have different absorption spectra. All are unique about which colors are absorbed and which pass through. This plays a major role in identifying gems and it is easily distinguished between an imitation gem to the real thing. To determine the absorption spectra of a mineral, a spectroscope is used.

Acicular
It is an aggregate of long, slender, crystals i.e. Natrolite. The term is also used for the crystal habit of a single long, thin, slender crystals.

Agate
It is a type of chalcedony which is found in many different patterns and colors, often with varying color layers.

Aggregate
It is a term given to the grouping of crystals. It is defined by the way crystals are clustered together.

Amethyst
It is a crystallized and transparent quartz, found typically in violet or purple. It is the birthstone for the month of February.

Aquamarine
It is a semiprecious blue colored stone from the beryl family. It is the birth stone for the month of March.

Artificial stone
A look alike gem material which is either a manmade imitation or a synthetic.

Baguette
It is a rectangular style of a step cut and used for small gem materials.

Baroque
It is a term used for irregular in shape, like baroque pearls, tumble-polished stones, or freedom shaped gem materials.

Bead
It is a small stone which has been cut into a sphere shape.

Beryl
It is a lightly colored mineral, called emerald when transparent and dark green and known as aquamarine if the color is blue.

Birthstones
Each month of the year has a particular gemstone associated to it. They are as follows:
January - Garnet
February - Amethyst
March - Aquamarine
April - Diamond
May - Emerald
June - Pearl, Alexandrite
July - Ruby
August - Peridot
September - Sapphire
October - Opal, Rose
November - Yellow Topaz, Citrine
December - Blue Topaz

Blemish
It is a term used to any surface imperfection on the surface of a gemstone. As for example of a diamond, one would be referring to a nick, knot, scratch, abrasion, minor crack or fissure (cavity), or a poor polish.

"Blue-White"
For many years, this term was used in trading of a diamond without its distinctive body color. Now, according to the Federal Trade Commission, diamonds with a distinct blue body color will be trades as "blue-white."

Boule
It is a synthetic gem which is created from molten liquids placed in a tear shaped molds to crystallize, leaving them with a tear-like form. It is mostly applied for synthetic Rubies and Sapphires.

Brilliance
It is the term used for the total amount of white light returned to the eye from a diamond or any colored stone as the result of internal and external reflections. The factors which affect the amount of brilliancy in a gem are the refractive index, proportions, polish and transparency.

Brilliant cut
It is the most common style of diamond and many other gemstones cutting that consists of a combination of triangular and kite shaped facets. There are 57 or 58 facets in a round brilliant cut.

Cabochon
It is an unfaceted cut stone of a domed form, having a convex surfact. It is often also called as "cab."

Cameo
It is a carved gem or shell where the outer layers are cut away in such a way that the design stands out in relief against a background of a different color.

Canary
It is a term which refers to diamonds with an intense yellow hue. If the yellow make the stone very distinctive, then the term "fancy yellow" is also often used.

Capillary
The aggregate which is composed of tiny, thin, straight, long crystal strands; hairlike. Example: Millerite.

Carat
It is a unit of metric measurement used for gems. It is abbreviated with 'ct.' One carat is equal to 100 points, 200 milligrams, 1/5 of a gram.

Carbon spots
It is a black-appearing inclusions in diamonds, which is caused by the addition of graphite or homblende minerals.

Carbonates group
It is a group of minerals which contain one or more metallic elements along with the carbonate radical (CO₃). Most of them are lightly colored and transparent in pure form. All the carbonates are soft, brittle, and effervesce when they are exposed to warm hydrochloric acid. The carbonates are divided as Calcite group, Aragonite group. Sometimes, the Nitrates and Borates are also considered as a category of the carbonates.

Carlsbad twin
It is form of penetration twinning where the two Orthoclase crystals form interpenetrating twins.

Cassiterite twin
Two crystals which twin in a repeated pattern. It is also known as "repeated twinning."

Change of color (color change)
It is a phenomenon, only in some colored stones, where the gem material appears in different color in different types of light. This is usually caused by selective absorption and/or transmission of specific type of light to which the gemstone is exposed.

Chalcedony
It is a term which refers to the various types of colored stone, including milky, carnelian, agate, cat's eye and also jasper.

Chrysoberyl twin
It is a form of contact twinning where six Chrysoberyl crystals join at the base to form a six-pointed formation.

Citrine
It is a brownish-orange quartz variety. It is the birthstone for the month of November.

Clarity enhanced
It is also sometimes called "fracture filled." It is a term used for a gemstone which has been treated for the improvement of its appearance by filling fissures or fractures with a transparent substance.

Clarity grade
Diamonds are ranked on a scale from flawless, which is no inclusions visible under 10x magnification, to included i.e. eye visible inclusions. Clarity grade is one of the such four value factors.

Cleavage
It is the tendency of a crystalline mineral to break in a certain definite directions called cleavage planes. The breakage of such cleavage is done by cleaving. Cleaving is a process where a stone is studied in order to define the plane and divide it with a swift blow. The swift blow splits the stone into proportions quickly as opposed to sawing.

Colored stone
It is a name given to all natural gemstones, leaving diamonds or colored diamonds.

Color grade
Diamonds are ranked on a scale from "D" to "Z." "D" for colorless and "Z" for noticeable tint of color, typically yellow or brown. Diamonds with saturation greater than "Z" color are considered to be Fancy Colored Diamonds and are graded on a separate scale. Color grade is referred to one of the four value factors of the diamond.

Color origin
It is a term used for the determination of the cause of color in fancy colored diamonds. Diamonds which are naturally colored are very rare and expensive. The two common ways that enhance the color of diamonds are irradiation and the high pressure and high temperature (HPHT) process.

Corundum
It is a crystallized aluminum and oxygen gem mineral. The most valuable type of corundum are ruby and sapphire.

Crown
It is the part of any faceted gemstone above the girdle.

Culet
It is the small facet polished across a stone, otherwise it would have been a sharp point or tip of the pavilion of a faceted stone, especially a round brilliant cut. The main purpose of this cut is to avoid breakage of this tip.

Cultured pearl
It is a pearl which is being produced by implanting a shell bead or mantle tissue into the body of a pearl which bears mollusk. The leading cultured pearl producing countries in the world are Japan, China, Tahiti, Australia, the U.S., and the Persian Gulf.

Diamond
It is a mineral which crystallizes in the cubic system and is composed of carbon with a hardness of 10 on Mohs scale. Its refractive index is 2.417 and specific gravity, 3.52.

Dispersion
It is a term used for the separation of white light into its component spectral colors. (also see fire).

Double refraction
It is a term given to the phenomenon which is exhibited on all non-opaque minerals, leaving amorphous ones and those that crystallize in the isometric system. When a ray of light enters the crystal, it splits up into two separate rays and makes everything observed through the crystal appear as double. In many minerals it is very weak and is observed only through special instruments but in some minerals like Iceland Spar variety of Calcite is strongly visible. Double refraction differs from mineral to mineral. This property is used in identifying gems. It is measured with a refractometer.

Doublet
There are many gem fakes, one of them is this. In it a thin, flat section of a real gem is pasted atop a thick base of glass or rock crystal.

Doubly terminated
It is a term for exhibiting a pinched crystal figure on both bases.

Durability
It is a combination of hardness, toughness and stability which describes the specific gemstone's ability to resist wear.

Emerald
It is the green colored beryl and among gemstone it is one of the most valuable one. It is the birthstone for the month of May.

Emerald cut
It is a style of cutting a gemstone where the outline is of rectangular shape with cut corners and the shape of the facets are rectangular and trapezoid.

Engrave
It is a term used to carve letters or image out of a gemstone.

Erosion
It is a process in which rocks are worn away from natural procedures, like water and wind.

Face
It is a term for an individual flat section of a faceted gem.

Facet
It is one of the small and flat surfaces of a gemstone which is polished to increase its brilliancy and beauty. A round brilliant cut gemstone has a total of 57 or 58 facets.

Faceted
It is the gem of plane faces or facets.

Faceted girdle
It is a girdle of a stone which is lapped and polished for its maximum surface reflection. It has many flat planes around the circumference of the stone.

Feather
It is a fracture or break in a gemstone which is typically white and feathery in appearance.

Finish
It is a term which refers to the quality of fashioning a gemstone, including the polish and symmetry.

Fire
It is the flashes of spectral colors which are seen in a gemstone as a result of dispersion.

Flaw
It is an inclusion or a crack in gemstones which generally demotes its value.

Fluorescence
It is the process of a material which emits visible light when it is subject to ultraviolet light. As an example, diamonds under UV light often emits a visible light of a blue hue.

Four C's
It is cut, color, clarity, and carat weight. This phrase is used to describe a diamond's value characteristics.

Fracture
It is a break within a gemstone.

Freshwater pearl
It is term given to a pearl which forms in a freshwater living mollusk.

Full cut diamond
It is a description of a brilliant cut, a round stone with 57 to 58 facets.

Garnet
It is a semi-precious stone and a family of crystal, generally in reddish-brown color but even ranges from true red to violet or blackish red. The name has been derived from its resemblance to red pomegranate seeds. The red garnet is the birthstone for the month of January.

Garnet paper
It is a sandpaper which is composed of tiny, hard, garnet crystals, glued on it for the use of an abrasive.

Gem or Gemstone
It is a precious or semi-precious stone that is cut and polished for the use in jewelry.

Gemology
It is the science and procedures being involved in mining, faceting, and also marketing of gemstones.

Gemologist
It is a term for an individual who is practicing in the subject of gemology.

Genuine pearl
It is a smooth and round growth formed within the mollusk shell due to an irritant. It is used as gem.

Girdle
It is the narrow band around the widest part of a polished or faceted gemstone, which divides the crown and pavilion facets.

Habit
It is the attributes of crystal's or aggregate's appearance.

Hardness
It is the ability of a gem to resist scratching.

Heat treated
It is in reference to a mineral or a gem which is put under intense heat to enhance color or remove flaws.

Hemimorphic
It is in reference of a doubly terminated crystal which has two differently shaped ends.

Hexagon
It is a term for polyhedron with six sides and a top and bottom base.

Hexagonal (crystal system)
It is for any of the mineral that has four axes out of which three are equal in length and lie at an angle of 120° from each other. The fourth one may be long or short but at right angle toward the other corners.

High polish
It is a surface which has been polished to a mirror-like finish.

Hopper
It is a form of crystal which exhibits an indenting, terraced, structure penetrating towards the center.

Hue
It is the primary impression of color like red, green or blue.

Inclusion
It is the internal characteristics present in gemstones. The common inclusions in diamond includes feathers, crystals, fractures, graining, pinpoints, cavities, etc.

Iolite
It is a mineral which is used as a gemstone. It occurs in deep blue, purple, light blue-gray, and yellow-white.

Iridescence
It is the prismatic colors inside or on the surface of a material which is caused by light interference from thin layers of differing refractive indices. The layers may be thin films of liquid, gas or solid. Pearls are best known for their exhibiting iridescence.

Japanese twin
It is a type of contact twinning where two single quartz crystals are joined from their base at an angle near 90°.

Lapidary
It is a term used for an individual who facets gemstones as a trade. The shop of such individual is also called such. It is even sometimes used in adjective form relating to gems, like lapidary equipment.

Loupe
It is a small magnifying lens which is used to observe certain aspects of gemstone. It commonly have a magnification level of 10x.

Luster
It is the quality of the reflected and refracted light from the surface of a gemstone or pearl.

Macrocrystalline
It is a term for having large crystals which can be easily seen with a naked eye.

Mafic
It is a term used for describing the dark colored rocks or minerals which is composed of magnesium and iron.

Make
It is the trade term which refers to the proportions, symmetry, and polish of a gemstone.

Marquise
It is a term used for the fashioning style for gemstones which has the girdle outline in an elliptical shape with pointed ends.

Matrix
It is a material which has an embedded crystal inside or emerging from it.

Matte
It is a term which refers to a non-shiny, frosted surface.

Melee
It is a term used generally to describe small, round faceted diamonds or the colored stones of approximately 0.18 carat or less.

Mohs scale
It is a loose scale of hardness devised by a German mineralogist, Friedrich Mohs in the 19th century. It is used for field collecting, which allows for identification of specimens. The comparative scale of hardness is as follows:
1) talc
2) gypsum
3) calcite
4) fluorite
5) apatite
6) moonstone
7) quartz
8) topaz and beryl
9) corundum
10) diamond

Mollusk
It is a family of marine creatures having soft fleshy body surrounded by a calcareous shell. It includes the oyster and snail.

Moonstone
It is a translucent stone which is often bluish in color, yet sometimes white.

Mother-of-pearl
It is a term for the iridescent inside of a mollusk shell that is used as an ornament. It is different from pearl.

Mounting
It is a trade term for particular portion of a piece of jewellery in which a gem or other object is set.

Multicolored
It is term for exhibiting two or more of colors on a single specimen.

Nacre
It is the secretion of iridescent substance by a mollusk during the formation of a pearl. It consists of layers of aragonite and calcite crystals.

Natural
It is a trade term for a particular portion of the original surface of a rough diamond left by the cutter while polishing and faceting a diamond. Naturals are generally found near the girdle of a diamond and are represented in green on a plotting diagram.

Natural pearl
It is a name given to a pearl which originates naturally in a mollusk. It is distinguished from cultured or imitation pearls.

Nick
It is a minor chip on the surface of a diamond which is generally found near or on the girdle of the stone.

Onyx
It is a semi-precious stone which is composed of chalcedony and is found naturally in white or gray. The white variety of the onyx is generally dyed black.

Opal
It is a non-crystalline, iridescent silica. It is the birthstone for the month of October.

Opaque
It is term which refers to the transparency of a gemstone. Opaque materials do not transmit light.

Orient
It is the soft iridescent glow on or just below the surface of a pearl or cultured pearl. Orient is caused due to the interference and diffraction of light from the minute crystals comprising the pearl's nacre.

Oval cut
It is a fashioning style for gemstones which has the girdle outline in an elliptical or oval shape.

Pave
It is a style of setting of small stones to the maximum possible closeness in two or more rows.

Pavilion
It is that portion of a faceted diamond or any other gem material which lies below the girdle.

Pear shaped cut
It is the fashioning style fo gemstones with the girdle outline in the shape of a tear drop or pear.

Peridot
It is a transparent gem which is olive green in color. It is the birthstone for the month of August.

Plotting diagram
It is a schematic diagram included on the EGL USA Diamond Certificate. It illustrates the facets, printed in black, of a diamond and the approximate location and type of internal and external characteristics, printed in red and green.

Point
It is a measurement in the weight of a diamond. One point is equal to 1/100 of a carat. Hence, 0.50 carats is equal to 50 points.

Polish
It is the smoothness of the surface of a fashioned gem. On it the optical reflection is maximized and it shows no visible wheel or burn marks.

Polished girdle
It is a girdle which has been lapped or polished to yield a uniform and a highly reflective surface.

Precious stones
It is rare and costly gems like diamonds, emeralds, sapphires, and rubies.

Princess cut
It is a modification of a brilliant square-cut gemstone. It is generally square-shaped in diamonds.

Quart
It is a crystalline mineral which is used for gems, including amethyst and rock crystals. It is available in variety of colors.

Radiant cut
It is a type of cut which is usually found in diamonds.

Reflection
It is the return of light after striking the surface of stone.

Refraction
It is the change in the direction of a ray of light which enters a gemstone.

Rhodolite
It is a variety of garnet which ranges from rose-red to pale violet.

Rough
It is any of the uncut or unpolished gem material.

Ruby
It is a precious stone which is highly valued. The most common color of the stone is red. Red colored ruby is the birthstone for the month of July.

Sapphire
It is a precious stone from the family of corundum. It is highly valued and the most common color seen is blue. The blue colored sapphire is the birth stone for the month of September.

Satin finish
It is a matte finish which is made by sandblasting, brushing with a stiff wire brush or then by chemically altering a high shine surface. Satin finish has a soft, pearl-like luster instead of bright polish.

Scintillation
It is a mirror-like reflections from the facets of a gemstone as it turns in the light.

Semi-precious stones
Any stone which is suitable for use in jewelry but is not a diamond, ruby, sapphire, or emerald. Few examples of semi-precious stones are amethyst, aventurine, carnelian, garnet, opal, and rose quartzes. Semi-precious stones are quite costly.

Simulated stones
It is any substance which is fashioned to imitate the appearance of a gemstone.

Single cut
It is a brilliant round cut which has 17 or 18 facets: 8 bezel, 8 pavilions, a table and a culet facet.

Smoky quartz
It is the quartz which are brownish in color, with a smoky appearance.

Solitaire
It is a term used to refer to a ring containing a single diamond or any other gem.

Star facets
It is the eight triangular facets which surround the table facet of a round and brilliant cut diamond.

Step-cut
It is a type of gem cut with a varying number of sloping parallel rows of four-sided facets which give the impression of harder.

Symmetry
It is a term used to refer to the quality of the fashioning of a gemstone. In symmetry grade the consideration is the balance of the outline shape and the precision of the facet arrangement.

Synthetic
It is a man made gem material with same physical, optical and chemical properties as that of its natural counterpart.It is a man made gem material with same physical, optical and chemical properties as that of its natural counterpart.

Table
It is the horizontal and top flat facet on the crown of a faceted gemstone. The percentage of the table is a comparison of the table facet size to that of the width of the stone at the girdle.

Tone
It is an attribute of color which determines its lightness or darkness of shading.

Topaz
It is a transparent gem. Wine-yellow colored topaz is the most precious one. Other colors which exists in topaz are white, blue, brown, orange, and pink. Blue colored topaz is the birthstone for the month of December.

Toughness
It is the breakage (fracturing) resistance ability of a mineral or gemstone. The toughness is different from the hardness of a stone.

Tourmaline
It is a crystalline mineral that is used as a gemstone. It comes in variety of colors but the most common of them are pink and green.

Transparency
It is the ability of a substance to transmit light.

Treated gems
It is a general term used in describing gemstones which have been artificially modified to improve their color or clarity. The techniques which are included are laser drilling, fracture filling (clarity enhancement), high pressure high temperature (HPHT) annealing, irradiation and surface coloration. The gemological laboratories have the equipment and experience to detect more difficult treatments.

Trillion
It is a term used for a triangular shaped and faceted gemstone. To be more specific, the term is used for a gemstone that has an arched shaped triangle cut with 25 facets of the crown and 19 facets on the pavilion.

Twin crystals
It is the two or more mineral crystals which have been grown together in a symmetrical nature, generally non-parallel. It is sometimes also known as twinned crystals.

Troy ounce
It is a weight unit practiced in England and the U.S. for precious metals. 20 pennyweights (dwt) is equal to one troy ounce, and 12 troy ounces is equal to one troy pound.

Ultraviolet light
It is the light that is invisible to the naked eye as it consists of shorter wavelengths than those of visible light.