Precious and Semi-Precious Gemstone and Mineral Glossary
Demantoid Garnet with Adamantine Lustermoonstone. Interference phenomena of the layered structure is the cause of this effect.
Amorphous GemstoneGemstones without a crystal structure are referred to as amorphous. These include gems such as amber, coral, opal and pearl. sapphires or rubies, for example. This is usually caused by tiny silk rutile inclusions in the stone. The effect can be four- or six- rayed. A long rectangular gemstone shape, somewhat similar in shape to a loaf of French bread, hence the name.
Baroque Cut (Diamond-Cut)A round shaped stone cut with a minimum of fifty-eight facets. An old faceting technique intended to maximize brilliance featuring eight-square symmetry often seen in modern-day diamond-cuts. drilled gemstone, usually round but can be foud in various other shapes, designed to be strung and hung. A form of heat treatment for sapphire that adds the element beryllium to the heating process. Beryllium is an element well known in the gem world, since it is an essential constituent in many gemstones, including emerald, beryl, and aquamarine. When sapphires are heated with beryllium, the result is a reduction in blue tones. Thus bright yellow or orange sapphire can be produced from weak yellow or greenish gems. Some stunning colors have been produced using this method. A gemstone exhibiting two color zones, such as ametrine or many tourmalines. diamond, spinel and garnet. A gem that is cut round without facets into the shape of a smooth polished dome. It lacks the facets that are on most faceted stones. See Chatoyancy. The center stone is the prominent center piece in a jewelry setting that has multiple gemstones. See also Side Stone. Thai Gems trading. Chanthaburi is also famous for its weekend gemstone market.
chrysoberyl, apatite and tourmaline is known by the technical name of chatoyancy. The effect is caused by tiny parallel inclusions that give the appearance of a narrow line similar to a cat's eye. Often a gemstone needs to be viewed in natural light to see the chatoyancy effect. color. color zoning) A term that describes the uneven distribution of color in a gemstone. Zoning is best seen when looking at the stone through the top table facet. Color zoning examples can be very easily seen within bicolor ametrine; exhibiting both golden citrine and violet or purple amethyst in a single crystal.
Color Change (gemstones)Color change gems change color due to changing light conditions (such as alexandrite or color change sapphire) or when viewed from different angles (such as andalusite or iolite). Traditional gem facets are flat or two-dimensional. Concave cutting creates facets that are curved or three-dimensional. These curved facets refract more of the ambient light and return it to the eye as brilliance. Concave cutting is a recent innovation dating back to the early 1990s. It requires considerable expertise and results in higher weight loss to the rough stone, since more material must be cut away to create the curved facets.
Corn Flower Blue (sapphire)The best Sri Lankan sapphire is descriped as being a rich 'cornflower blue' - said to rival that of fineÂ Kashmir SapphireÂ and Burmese sapphires. Cornflower blue is described as light and bright, rather than deep and inky blue. Gemstones that contain traces of copper are very rare and typically have a intense blue, blue-green or violet color. There was considerable excitement in the gem world when the first copper-bearing gemstones were discovered in 1989. See also Paraiba. ruby and sapphire. It is naturally clear, but can have different colors when impurities are present. Corundum is much admired for its hardness (9.0 on the Mohs scale), brilliance and excellent wearability. the Mohs scale of hardness, CZ is harder than other gemstones except for diamond, ruby, sapphire and chrysoberyl. Not to be confused with zircon, a natural gemstone. Copper-bearing. Learn about copper-bearing gemstones.
Ceylon Blue (sapphire)A light to medium blue color of gem-quality corundum originating from Ceylon (Sri Lanka). Sri Lanka is now one of the world's leading producers of fine sapphire. andradite garnet. It exhibits a range of greens from dull to bright emerald green and on rare occasions displays yellow. On the Mohs scale of hardness, demantoid is relatively soft at 6.5. It has an adamantine luster. Also known as the brilliant cut, the style of cutting a stone with multiple facets to maximize brilliance. Modern round brilliant cuts have 58 facets. A form of heat treatment that adds one or more chemicals to the heating process to change the color of a gemstone. Typically the treatment does not penetrate deep into the stone, so gems treated in this way cannot be recut. Diffusion treatment is a standard treatment to increase the asterism in star sapphire. Diamond has a very high dispersion, hence its high amount of "fire".
Double RefractionThe ability of most gems to split rays of light into two unequally refracted rays. Also called 'birefringence'.
DoubletA doublet is a gemstone composed of valuable gemstone material in combination with other materials. It is found most often seen in gem types such as ammolite or opal; an opal doublet contains a slice of opal glued to common opal, glass or other material. A triplet contains a slice of opal glued between a base and a crystal or a glass top. Triplets are usually less expensive than doublets, and both are less expensive than natural opals. Doublets may occasionally be found with sapphire or other expensive gemstones. inclusions or imperfections to the naked eye. Compare Loupe Clean. facets on a stone. dispersion. fracture filled. emerald, turquoise and ruby. cleavage are likely to break when being cut or faceted.
Gemstone Point (measurement)A gemstone unit of weight equal to 1/100 of a carat, often used in reference to diamond weight; e.g., a 5 point diamond is equal to a 0.05 carat diamond.
Gemstone RoughIn gemology, this refers to the raw, natural state in which gems are found, before they are cut. luster of a gemstone. Jadeite is an example of a gem with a greasy luster.
Heat TreatmentThe application of high heat to a gemstone in order to improve its color and clarity.
HueRefers to the position of a color on the color wheel, or the dominant wavelength of color attributed to a gemstone. There are six primary hues: violet, blue, green, yellow, orange, and red. In between these primary hues are secondary hues, such as blue-green. See also tone and saturation. inclusions and they are important visual clues for identifying the type of gemstone and for identifying the origin of the stone. Blue tourmaline. From bright blue hues to bluish green colors, indicolite tourmaline is one of the rarer tourmaline colors. topaz is always irradiated, for example. Karat (as distinguished from Carat) is a measure of the purity of gold. Most gold jewelry is actually made from a gold alloy containing gold and another metal or metals. 18K gold, for example, is 75% pure gold.
Lab created (synthetic)Refers to gemstones created in a laboratory rather than by nature. A lab created gemstone is typically the same material chemically as its natural counterpart, as in the case of corundum produced by flame fusion or quartz grown using the hydrothermal method. See also Eye Clean.
LusterThe outward appearance of a gem or organic material. The quantity and quality of light that is reflected from the surface of a stone. Luster is important especially when evaluating the quality of pearls.
Metallic LusterOne of the technical terms used to refer to the luster of a gemstone. A gemstone that is reflective like polished metal is said to have a metallic luster. Hematite and labradorite are some of the better examples. A numerical scale ranging from 1 to 10 developed by Friedrich Mohs that assigns a rating to a gem according to its ability to resist scratching. The hardest is 10 (diamond) and the softest is 1 (talc). the Mohs scale of hardness, moissanite is 9.5. It has more brilliance, fire and luster than any hard jewel on earth, including diamond.
Oiling TreatmentOiling infuses colorless oils, resins or waxes into tiny surface-breaking fissures to hide them and give certain gemstones a cleaner appearance. This long-practiced clarity enhancement is used mainly for emerald and jade. The oils used are either natural or have a natural counterpart. If coloring agents are added to the oil, the stones are classified as dyed rather than oiled. Lapis lazuli and malachite examples of opaque gemstones. See also Amorphous gemstones. padparadscha refers to a lush pink and orange sapphire resembling the color of the lotus. Padparadscha is also sometimes used to refer to other types of gemstones, such as topaz and tourmaline, with this unique coloration. See also Copper-bearing. optical properties such as color change, chatoyancy, asterism or iridescence. rubies. Pigeon's blood red is thought to be a pure red with a hint of blue. It is associated most with rubies from Burma, though any ruby could be this color. The classic precious 4 gemstones are diamond, emerald, ruby and sapphire. However, new precious gems are being added, such as precious coral, opal and topaz. emerald. But other gems have also been labelled precious at times, including opal and amethyst. Today, the distinction between precious and semi-precious gems has been rejected by some gem trade associations. See also Semi-Precious gemstones. View Refractive Index Chart. A process using a refractometer to measure the speed and angle of light entering a gemstone. Very important for gem identification. Used to refer to the red variety of tourmaline, including the color range from pink to red. More of a marketing than a gemological term; these days gemologists tend to use simply "red tourmaline." Needle-like inclusions (or foreign matter) within stones. These can produce some gem phenomena such as asterism (star) or cat's eye (chatoyancy). Saturation is one of three characteristics used to describe the appearance of color. Saturation (also known as intensity) refers to the brightness or vividness of a color. See also hue and tone. precious gemstones are diamond, ruby, sapphire and emerald. Semi-precious gemstones include everything else. But other gems have also been labelled precious at times, including opal, amethyst and pearl. Today, the distinction between precious and semi-precious gems has been rejected by some gem trade associations. See also Precious gemstones. spinel and garnet. See also Birefringence. Center Stone and Side Stone. sapphire and ruby. The quartz family contains amethyst, citrine, and chalcedony, to name a few. see density -- View specific gravity chart. heat or irradiation are not classified as synthetic. See also Saturation and Hue.
TranslucentA quality of a gemstone transmitting light imperfectly so that one cannot see through the stone clearly. Star sapphire is an example of this quality. See also Translucent and Opaque.
Treated stoneA stone that has been heated, dyed, irradiated, or stained in order to improve the color or the clarity. Also pertains to gems that have their cracks or fractures concealed by filling the material.
Vitreous LusterA technical term referring to the luster of a gemstone; vitreous luster is synonymous with glass-like luster. Gemstones with a vitreous or glassy luster are by far the most common in the gems world.
WaxyOne of the technical terms used to refer to the luster of a gemstone. Turquoise is an example of a gem with a waxy luster.
- First Published: October-23-2006
- Last Updated: November-08-2018
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