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Gemstone Terms for Jewelers
Expand your gemstone vocabulary with this glossary of terms and definitions.
Last edited: 10/31/2019
What is the difference between a cabochon and a faceted gemstone and why are there so many different cuts? Gemstones and pearls add another layer of specific terminology that is used in jewelry making. Bookmark this gemstone glossary for the next time you come across a term you’re unfamiliar with.
Cultured in the Akoya pearl oyster (pinctada fucata martensii) and primarily found in Japan and China, they are lustrous and are generally white or cream colored with overtones of rose, silver or cream. Akoya pearls are renowned for their incredible luster and are considered the classic pearl. They are more smooth and round than Freshwater pearls.
Any stone that has been changed in appearance, particularly in color, by artificial process.
The term "artificial" is a catch-all for any manmade, imitation, simulated or lab-created gemstone. Simulated gems with no natural counterparts fall into the category of artificial and are used as simulants. Artificial gems that have the same chemical, optical and physical properties as their natural counterparts are more accurately described as synthetic or lab-grown.
A gem constructed of two or more parts. Includes foil-backed stones.
A thin film of metal, nitrides and oxides applied to gemstones by vapor deposition. Gemstones with this coating require special care; do not use harsh detergents and never steam or ultrasonically clean.
A small gem cut in a long rectangular shape, usually used as accents to larger stones.
A nick, scratch or other mark on the surface of a stone, as opposed to an inclusion, which exists in (or reaches into) the stone's interior. Blemishes should have little impact on a stone's value and beauty because they can usually be removed easily by polishing.
The reflection and refraction of light displayed through a stone. Brilliance is generally applied to diamonds but can also refer to colored gemstones.
The style of cutting a stone with multiple facets in a particular way to maximize the gem's brilliance. Modern round brilliant-cut stones have 58 facets.
A three-dimensional stone with triangular facets cut across the surface. Briolettes differ from most other gemstone shapes in that they appear the same from every direction—without a table and pavilion—making them ideal for dangling earrings or pendants.
A figure or scene carved in relief by cutting away background material in stone or shell. In many cases, these materials offer alternating bands of color, or shades of color that provide contrast to the raised portion of the cameo. A cameo artist takes advantage of different layers and faults in the material to enhance the design as they carve.
A unit of weight for precious stones. Abbreviated as "ct."
Gemstones can contain a wide variety of inclusions. In faceted gems, inclusions are defined as anything that will interfere with the free passage of light. These can include little bits of minerals, hollow areas, and fractures. Clarity gemstone grading addresses the visual and structural impact of these things.
Gemologists describe gemstone color by referring to three properties: hue, tone and saturation. The highest values go to stones with pure hues and strong, rich colors.
An extremely hard mineral composed of aluminum oxide, sometimes in addition to iron, magnesium or silica, that occurs in gem varieties such as ruby and sapphire. Corundum comes in all color of the rainbow, plus black and white.
The upper portion of a gemstone that begins just above the girdle and surrounds the table of the stone.
The cubic crystalline form of zirconium dioxide. The synthesized material is hard and optically flawless. Clear (or white) cubic zirconia are usually colorless and are economical alternative to diamond. CZ are available in a variety of different colors. It should not be confused with zircon, which is a zirconium silicate.
The bottommost facet on the pavilion of a round gemstone. It is cut parallel to the table and is generally the smallest facet on a stone.
The only gemstone composed of a single element—carbon. It is also the hardest natural gemstone, holding the position of 10 on the Mohs hardness scale. Diamonds come in all colors of the rainbow. Those not represented on the normal diamond color-grading scale are known as fancies, the rarest being red diamond. Color in diamond is caused by structural irregularities or trace elements.
A gemstone with crown and pavilion facets like diamonds.
The separation of white light into spectral colors in diamonds and gemstones. In simple terms, dispersion is the sparkle that you see when you turn or tilt a gemstone.
Any assembled gemstone that is manufactured from two components held together by a transparent bonding agent. The types of materials used for doublets vary considerably. A triplet is created from three components.
A combination of hardness, toughness and stability.
Enhancement is a process that improves a natural gemstone's appearance or durability by an accepted industry practice. Gemstones that undergo one of these processes are called enhanced gemstones. Rio Grande discloses all enhancement using American Gem Trade Association (AGTA) standards.
The art of cutting facets, or flat faces, on the geometric shapes of precious and semi-precious gemstones. Faceting improves the appearance of gemstones by facilitating and enhancing the stone’s ability to reflect light, creating a dazzling and brilliant sparkling effect.
A fancy cut is any shape other than the traditional round. It is synonymous with fancy shape. Examples of fancy cuts include marquise, pear, oval, heart, square and cushion.
The result of an optical property known as dispersion. The term is used to describe the rainbow-like flashes of color that are commonly seen in diamonds and other gemstones. Each color represents a wavelength within the spectrum of visible light—red, orange, yellow, green, blue and violet. Fire is best seen in colorless or lightly colored gemstones, since deeper, richer colors tend to mask the effect.
A fracture that reaches the surface of the gemstone.
Four Cs of Gemstones
The 4 Cs for diamonds and gemstones are: cut, color, clarity and carat.
Pearls that are cultivated in ponds, lakes and rivers, as opposed to saltwater environments.
The widest point of the circumference of a gemstone. It is the perimeter of the stone that separates the gem's pavilion from its crown.
The ability of the gemstone to resist scratching.
A stone with natural and artificial components, where the two cannot be separated. In most cases, undesirable elements of a natural material are removed and replaced by added artificial gem material, such as lead glass, polymers or synthetic material. Some require special care.
See simulant. The term imitation is used to describe any material that mimics the appearance of a natural or more expensive gemstone. Imitations may be manmade or natural. Examples: red glass (imitation ruby), white YAG (imitation diamond), red garnet (imitation ruby)
A manmade look-alike that may be produced from glass, plastic or some other inexpensive material. It is sometimes called a faux pearl.
An internal characteristic of a mineral or gemstone. Its external counterpart is called a blemish. Inclusions take many forms and often provide important information about the formation and/or origin of the gemstone. Inclusions may be large and visible to the naked eye (macroscopic) or extremely small (microscopic), requiring some form of magnification.
Gemstones that are custom-cut to fit recessed areas within the jewelry piece. A bonding agent is used to hold the gem materials in place.
Stones grown in a lab that have the same mineral content as their natural counterpoints. They are chemically, physically and optically identical to those mined from the ground—but they have fewer inclusions and cost less. These stones are sometimes difficult to distinguish from the natural stones in gemological identification tests.
The Mohs hardness scale was developed in 1822 by Frederich Mohs. This scale is a chart of relative hardness of the various minerals (1 being softest and 10 being hardest). The Mohs scale of mineral hardness characterizes scratch resistance of various minerals through the ability of harder material to scratch softer material.
A natural gemstone is formed in the earth and can be enhanced to improve the appearance or durability of the stone.
A silky substance secreted over a nucleus or other irritant during the formation of a pearl. Layer after layer of nacre builds up to form the pearl.
The lower portion of a gemstone that begins just below the girdle.
Refractive index, or RI, is one of the most important signatures of a gemstone. Refraction is the bending of light as it passes in or out of a gemstone. The angle of refraction in the stone determines its refractive index. Gemstones with a high refractive index are more brilliant than those with a low RI.
Historically, rock crystal that was faceted into beads from the Rhine River. Now rhinestone is made from crystal glass.
The rose cut features a flat base (no pavilion) and a crown made up of triangular facets symmetrically arranged in a circle and rising to form a point at the top of the stone.
The area of a cabochon where the straight sides start to round to create the head of the stone. This is the area where a bezel locks the stone into a setting. Shoulder is also used to describe the upper part of oval and pear-shaped faceted gemstones.
The term "simulant" is synonymous with substitute or imitation. A simulant only mimics the visual appearance of a more expensive gemstone. A simulant usually indicates a manmade material but may be natural. Simulated gemstones carry a relatively low value due to the inexpensive costs of materials and production. Some of the higher-end simulants use synthetic moissanite, or silicon carbide, which features crystalline properties similar to quartz.
A way to express the relative density of a gemstone. Abbreviated as “S.G.”
The ability to remain unchanged in the presence of heat, light and/or chemicals.
Standard Pearl Processing
Routine cleaning and bleaching of cultured pearls.