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Gemspedia >> Gems >> Gemstone Glossary

Gemstone Glossary


Stones those have been sourced from alluvial deposits in river beds or transported by water and deposited in seas and lakes. Many gems, including diamonds, are found in alluvial deposits and Alluvial stones are usually of gem quality.

American Cut

Marcel Tolkowsky’s mathematically calculated ideal proportions and facet angles, to produce maximum brilliancy consistent with a high degree of fire in a round brilliant gemstone. This is known as American Cut or Ideal Cut.


Asterism is the star effect that appears on some gemstones. This star effect is a reflection that appears as two or more intersecting bands of light across the surface of a gem. Usually asterism is found in Ruby, Sapphire and Garnet.


Aventurescent gemstones are those which display a colorful play of sparkling reflections due to small metallic inclusions.


Baguette is a French word meaning ‘Rod’. It is a step cut for small rectangular shaped gemstones and diamonds.


Baroque is a term that refers to irregularly or oddly shaped stones mainly pearls. Baroque pearls can be natural or artificial.


The name beryl comes from ancient Greek word ‘beryllos’ which means precious blue-green color. This stone is available in a variety of colors including green, yellow, greenish-yellow, blue to blue-green, red, colorless and pink.


A birthstone is nothing but a stone, which is associated with the date of one’s birth and wearing of such birthstone is considered to bring good luck and health. Certain stones are believed to have Supernatural powers and their relationship with planets. Many cultures originally assigned a specific stone to signify birth during each sign of the zodiac but over the time this tradition has been shifted from the zodiac to calendar months. Following birthstones are assigned for every calendar month. January – Garnet, February – Amethyst, March – Aquamarine, April – Diamond, May – Emerald, June – Pearl / Alexandrite / Moonstone, July – Ruby, August – Peridot / Sardonyx, September – Sapphire, October – Opal / Pink Tourmaline, November – Citrine / Yellow Topaz, December – Turquoise / Tanzanite / Zircon / Blue Topaz.


Brilliance describes the reflections of white light returned to the eye from a gemstone. Brilliance is produced primarily when light enters through the table, reaches the pavilion facets, and is then reflected back out through the table. The major factors that affect the amount of brilliancy in a gem are refractive index, proportions, polish and transparency.

Brilliant Cut

Brilliant Cut is the most common style of gemstone cutting and it is called a brilliant cut because it is designed to maximize brilliance. The standard round brilliant cut consists of a total of 58 facets which covers 1 table, 8 bezel facets, 8 star facets and 16 upper-girdle facets on the crown; and 8 pavilion facets, 16 lower-girdle facets, and usually a culet on the pavilion, or base. Brilliant cut stones normally come in round shape, but there are modified variants in other shapes also.


This term is used for a long teardrop shaped gemstone with rose cut facets, which sometimes is also drilled to be used as a pendant.

Cabochon Cut

A cabochon shaped gemstone resembles a dome as it comes in round shape with no facets. Generally onyx stone is cut in a cabochon shape.


Cameo is a style of carving in which the design pattern is left and the surrounding surface is cut away leaving the design in relief. This is done to use the natural colors of the stone or shell to produce the different shadings of the carving.


The term Carat is used as a standard unit of measurement of the weight of most gemstones including diamond. The word comes from the carob beans which are known for its consistent weight and was used in ancient times to measure gemstones. One carat (ct.) equals 200 milligrams, or 0.2 grams (1/5 of a gram), or 1/142 of an ounce. There are 100 points in a carat. If all other factors are equal, the more a stone weighs, the more valuable it will be. It is sometimes incorrectly spelled ‘Karat’, but Karat refers only to the fineness of pure gold and gold alloys.


The term chatoyant is used for those stones that have ability to display or reflect a cat’s eye effect. This effect is caused by the precise occurrence of slight inclusions. A chatoyant gem exhibits a changeable silky luster as light is reflected within the thin, parallel, fibrous bands.


A curved break or absence of a tiny piece of a gemstone, caused by normal wear and tear, or by cutting.


Clarity is one of the main value factors of a gemstone which describes the absence or presence of flaws inside or on the surface of a gemstone. Gemstones are graded on a scale from Flawless (no inclusions or blemishes visible under 10x magnification) to Included (eye visible inclusions or blemishes). If other factors are equal, flawless stones are most valuable.


The tendency of crystalline minerals to break in one or more definite directions, producing more or less smooth surfaces. A cleavage may be caused by inherent internal strain or by a sharp blow. Cleavage is one of the two methods used by stone cutters to split gemstones in preparation for the cutting process. The other method is sawing.


A group of a number of extremely tiny white inclusions which gives a ‘cloudy’ or ‘milky’ appearance under 10X magnification. These clouds cannot be seen with the naked eye and generally does not significantly impact a gemstone’s clarity grade.


Color is the most important criteria in determining the value of a gemstone. Color is measured by tone and hue in a gemstone. In gemstones, color is more significant than clarity / cut and even subtle differences in hue can make a lot of difference in valuations.

Color Change

Few gemstones distinctly change their color when viewed under two different light sources. This feature is commonly found in Alexandrite, Sapphire and Color Change Garnet.

Color Grading

A system of grading gemstones color based on their hue or tone. Usually a well distributed hue is considered best for a gemstone.


Color Enhancement


Color enhancement is the improvement process of a gemstone’s color mainly by irradiation and HPHT (High Pressure, High Temperature).

Composite Gemstone

It refers to a gemstone which is assembled from several pieces, often used to imitate a gem.


Corundum is a hard mineral that exists in the form of colored crystals, such as Rubies and Sapphires.


This term is used for a mineral structure in which crystals are very small and due to that they are not even distinguishable through a microscope.


A crystal is a solid material that has a definite internal atomic structure. Its atomic stricture produces a characteristic external shape as well as physical and optical properties.

Crystal Structure

Crystals are divided in to seven groups on the basis of specific set of angular, geometrical and symmetrical specifications. All crystalline gems can be classified in one of seven groups based on the above specifications. These groups are cubic, tetragonal, hexagonal, trigonal, orthorhombic, monoclinic and triclinic.


The upper portion of a cut gemstone above the girdle which surrounds a large flat area on top known as table.

Cultured Pearl

A pearl cultivated by an artificial process that imitates the organic process by which a natural pearl is created. An irritant such as a bead, grain of sand, or piece of mantle tissue is inserted manually into the body of a mollusk and becomes the nucleus of a pearl, once that mollusk secretes nacre to cover the irritation.


A shape of gemstone, which ranges from square to rectangular and it has rounded corners and larger facets to increase its brilliance. Cushion Cut stones are also known as "pillow cut" stones.


The smallest facet, at the bottom of most round or brilliant cut stones, is known as culet. Its purpose is to protect the tip of the pavilion from being chipped or damaged. Most modern shapes have either no culet at all, or a small or very small culet.


Cut refers to the geometric proportions and finish of a gemstone. It is one of the most important factors in determining gemstone’s sparkle and brilliance. The stone should be symmetrical in all dimensions so that it will appear balanced, and so that its facets will reflect light evenly, which will provide good brilliance to stone.


The person who cuts and polishes rough gemstones and converts them into finished gemstones.


The process of cutting, grinding or polishing rough gemstones and converting them into finished ones.


This usually means a gemstone which has been cut too deep. This deep cut maximizes weight but sacrifices brilliance.


The height of a gemstone from the table to the culet which is measured in millimeters.

Depth Percentage

The depth percentage, which expresses how deep the gemstone is in comparison to how wide it is. In other words, the depth of the gemstone is divided by the average width. This depth percentage of a gemstone is important to its brilliance and value. The pavilion should be deep enough to allow light to bounce around inside the gemstone and be reflecting out to the eye at the proper angle.


The width of the gemstone, as measured across the widest part of the girdle.


This term refers to a gemstone that displays a different color or shade, which is other than the original gemstone’s color, when viewed from different directions or angles.


Dispersion is the ability of a gemstone, to separate white light into the colors of the spectrum. It is also called the stone’s fire.

Double Refraction

This term is used when each ray of light is split in two as it enters in a non-cubic mineral.


Doublet is a composite stone which is made of two components, usually cemented or glued together with a clear adhesive.

Drop Cut

A drop cut or briolette is a pear-shaped cut gemstone with triangular facets on top. This type of stone makes a nice pendant.

Emerald Cut

Emerald Cut gemstone is a square or rectangular shape stone with cut corners. This is also known as Step Cut because it has rows of facets, usually 48 to 50, that resemble a staircase. Due to its larger, more open table, this shape highlights the clarity of a gemstone but with fewer facets, this shape brings less brilliance than the other shapes.


Enamel is a powdered colored glass fused onto the surface of the piece of jewelry. It is a soft material and can be easily cracked or damaged. This should not be used on jewelry pieces, which are exposed to daily wear.


Engraving is a method of surface decoration in which a design is etched or engraved with a sharp tool.


Enhance or enhancement is the process to improve a gemstone’s color or clarity by using various methods like heating and oiling.

European Cut

A European version of ‘ideal’ cut which was used and preferred in Europe although it was never adopted as a common form of cutting. In this cut, gemstone‘s proportions were worked out mathematically for light falling perpendicularly on the crown.

Extra Facet

An additional facet placed onto a gemstone, usually to remove a small surface blemish. This extra facet is not required by the cutting style and symmetry.

Eye Clean

A term used in the jewelry industry to describe a gemstone with no blemishes or inclusions that are visible to the unaided eye.


A term used for flat or plane surface that make up the exterior form of a crystal.


A plane, polished surface on a gemstone which allows light to enter in a stone and reflect off through different angles.


Faceting is the process of placing facets on a gemstone. The shape and number of the facets give the stone its style of cut.

Fancy Cut, Fancy Shape

Any shape of gemstone other than the round brilliant shape is known as fancy cut or fancy shape. It includes marquise, emerald cut, heart shape, pear shape, etc.


A person with expertise in gemology is known as gemologist. There are many recognized courses available from various Gemological Institutes which offer study in gem identification, grading and pricing.

Gemological Institute of
America (GIA)

Gemological Institute of America (GIA) was established as a non-profit organization in 1931 by Roger Shipley. GIA maintains the highest standards for grading gemstones and it has one of the world’s most-respected and well-regarded gemological laboratories. GIA has developed and standardize the gemstone grading system that is used by nearly all other gem labs.


A gemstone is a mineral or rock, which can be used in jewelry after cutting or faceting and polishing. Gemstones are diverse in their beauty and many gems are available in a stunning variety of colors. Most gemstones have little beauty in the rough state and they may look like ordinary rocks or pebbles in their rough form. After a skilled cutting and polishing of a gem, full color and luster can be seen. Gemstones are classified into two categories, precious and semi-precious, on the basis of their characteristics. Precious stones include diamonds, emeralds, rubies, and sapphires whereas semi precious stones are Alexandrite, Amethyst, Aquamarine, Citrine, Garnet, Iolite, Onyx, Opal, Pearl, Peridot, Tanzanite, Topaz, Tourmaline etc.


Geode is a cavity within a rock which is a crystal line. It grows from inner surface to center in a gemstone. Usually geode found in Amethyst and Peridot stones.


Girdle is the widest part or outer edge of the gemstone and the dividing line between the crown and pavilion. The girdle can be rough (matt), faceted, polished or unpolished but a polished or faceted girdle doesn’t improve a gemstone’s grade. Most labs grade a girdle’s thickness, not its appearance and the descriptions of girdle thickness range as follows: extremely thin; thin; medium; slightly thick; thick; extremely thick.


Girdling is the process of giving a circular shape to a gemstone. In this process, a gemstone is held in a lathe, or in a cutting machine, and cut or shaped by another diamond or tool, called a sharp.


A recognized measure of an aspect of gemstone’s quality, mainly clarity, cut and color.


The process of evaluating a gemstone, and allocating grades to it.

Grading Report

A grading report or certificate is a statement, issued by an independent Gemological Laboratory, that at the time of evaluation, the gemstone in question has been examined, measured, and scrutinized by experienced gemologist and graders, using various gemological instruments, and determined to contain the characteristics as stated in the Report or Certificate. The grading report should accurately describe the proportions, weight, color, clarity, symmetry, polish and possible fluorescence seen in the gemstone.


The hardness of a gemstone refers it’s resistance to scratching on a smooth surface. Moh’s scale of hardness, which scales from 1 (very soft) to 10 (very hard), is useful for comparing the relative hardness of different gem materials. Diamond is the hardest known substance on Earth and it is graded 10 on Mohs’ scale of hardness. Hardness is directional in most gemstones.


Head refers part of the setting that holds the center stone or solitaire in place.

Heart Cut

The Heart shaped gemstone is essentially a pear-shaped with a cleft at the top and which typically contains 59 facets. Due to the complexity of the shape, skilled cutting is necessary to maintain the gemstone’s brilliance. Generally people prefer a heart shape stone for sentimental purposes. This shape is mostly used in pendants, but also suitable for most jewelry items.

Heat Treatment

Heat treatment is the process in which heat is offered to a gemstone for the purpose of improving its color.


Hue is an aspect of color which is a primary factor in viewing and grading gemstones.

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