Glossary

Alluvial Deposit

An alluvial deposit is clay, silt or gravel that was carried by a rushing stream and deposited in locations where the stream slowed down.

Carat
A carat is a measure of weight used when referring to gemstones. This is very different to the karat term used when referring to the purity of gold. A carat is defined as 200 milligrams. That means there are 5 carats to the gram. Each carat can be further divided into 100 points. This allows for small stones, generally those below 1 carat, being measured in points, rather than fractions of a carat.
Cardinal Gems
The Cardinal gems are a number of gemstones that were traditionally considered the most precious, above all others. This term is not generally used anymore. It started in antiquity and was based largely on religious use, and the perceived rarity of the stones at the time. Amethyst, one of the original Cardinal gems, was considered rare and thus highly valued, until large deposits were discovered in a number of areas.
Custom Cut
Custom cut gemstones are cut by professionals with the primary aim of achieving the best quality finished stone. These stones will demand higher prices, but there is usually no comparison between a custom cut gemstone and a production cut gemstone. With custom cut stones the meetpoints should meet, polishes should be perfect and the stone should be brilliant. If you are looking for an investment stone, it should be custom cut and should be amazing to see.
Deep Siberian
Deep Siberian is considered to be the ideal grade of Amethyst. It has a purple hue of about 75-80 % and blue and red tones of about 15-20%.
Dichroic
Dichroic referes to the ability of some materials to split visible light into defined beams of different colours (wavelengths). Dichroic material usually splits into two colours, though the term is used often even when the material produces several distinct colours.
Diffraction
Diffraction refers to the bending of light that occurs when a light wave encounters an obstacle or a slit. The light bends around the corners of an obstacle or aperture.
Facet
Gemstone facets are usually flat surfaces cut into the gemstone in a uniform and planned pattern. They generally cover all surfaces of a gemstone. In modern times gemstones can have curved surfaces, either concave or convex. The facets must be positioned accurately, according to specific angles, to best reflect the light back to the viewer, creating that wonderful brilliance we all love. The angles depend on the type of gemstone, each type of gemstone having a different refractive index.
Gemstone Crown
The crown of a gemstone is that part above the girdle. This is the top of the gemstone and thus the face you would normally view after the stone has been set in jewellery.
Gemstone Culet
The gemstone culet is the point at the bottom of the gemstone. To prevent chipping, in some gemstones the culet has a flat surface rather than a point.
Gemstone Girdle
The girdle of a gemstone is the widest part of the gemstone. It separates the crown from the pavilion. Looking from the top of the stone it defines its outline. Looking from the side the girdle is usually quite thin, though it needs to be thick enough so a jeweller can set the stone without breaking the girdle. A very thick girdle can be a good indication of a bad gemstone cut. To increase the weight of a stone some cutters cut a deep girdle. This can make the stone darker and harder to set, besides ruining the look of the stone generally.
Gemstone Keel
The gemstone keel is found on certain gemstone cuts, instead of a culet. Cuts such as the emerald cut and the oval cut can't have a point and instead have an edge called a keel.
Gemstone Pavilion
The pavilion of a gemstone is the bottom of the faceted stone. The area below the girdle.
Irradiation
Irradiation is the process used to expose an object to radiation, either by nature or artificially. If applied artificially it is done so to achieve a specific purpose, such as improving the colour of a gemstone. In the case of gemstones, the process mimics the process that can take place naturally, though over a much longer period.
Koine Greek
Koine Greek also known as Alexandrian dialect, common Attic, Hellenistic or Biblical Greek, was the common supra-regional form of Greek spoken and written during the Hellenistic period, the Roman Empire, and the early Byzantine Empire, or late antiquity. It evolved from the spread of Greek following the conquests of Alexander the Great in the fourth century BC, and served as the lingua franca of much of the Mediterranean region and the Middle East during the following centuries. It was based mainly on Attic and related Ionic speech forms, with various admixtures brought about through dialect leveling with other varieties. Wikipedia Koine Greek
Loupe
A loupe is a small magnifying glass used by jewellers and watchmakers.
Lustre
In mineralogy, lustre is the way light interacts with the surface of the mineral. Many terms are used to describe lustre. Terms such as adamantine, greasy, dull, vitreous and more. A common term is vitreous, which refers to a glassy lustre.
Meetpoint
A meetpoint is the point where three (3) or more facets meet.
Middle Ages
The Middle Ages in Europe (or medieval period) was a period that spanned the 5th to the 15th century. It started with the fall of the Western Roman Empire and continued through to the Renaissance. It is so named because it is the middle period of three traditional divisions of European and Western history. The three periods being Classical Antiquity, the Medieval Period and the Modern Period.
Mohs Scale of Mineral Hardness
The Mohs scale of hardness in minerals was created in 1812 by the German geologist and mineralogist Friedrich Mohs. It is a scale that characterises scratch resistance of minerals to other harder minerals.For example, how Sapphire is scratched by Diamond. While Mohs created this scale, the concept of observing how one mineral scratches another dates back to antiquity, being mentioned in the On Stones treatise by Theophrastus, c. 300BC.
Nacre
Nacre, the coating that appears on the inside of some mollusc shells, is an organic-inorganic compound. Nacre is also the natural coating applied to pearls by molluscs. It's a very resilient and strong surface that has beautiful iridescent appearance.
Prayer Beads
Prayer beads are used by the followers of various religions to count the repetitions of things like chants, devotions and prayers. These include the Bahá'í Faith, Buddhism, Christianity, Hinduism, Islam and Sikhism
Production Cut
Most gemstones in affordable jewellery today are generally produced in bulk, using a mass production cutting method. This may be by machines or low cost labour. This means that meetpoints may not meet, polishes may not be complete, brilliance may be less than desirable and so on. Production cut stones are cut for weight, because they are priced per carat, and not brilliance. This means that the correct angles may not have been used. You can see this in stones where the pavilion has been bellied out to give more weight. The table may also be higher than desirable. The alternative to a production cut stone is custom cut stone that has been cut to achieve the best looking stone, even at the cost of reducing the weight. However, custom cut stones demand a higher price per carat and thus the loss in weight is offset by the quality of the final stone.
Reflection
Reflection is the change in direction of a light wave at an interface between two different media, so that the light is returns back into the medium from which it originated.Your bathroom mirror being the perfect example.
Refraction
Refraction is the change in direction when a light wave passes from one medium into another. A common example can be seen when placing a stick into water and it appears to bend. In fact, the light from the stick is changing direction as it exits the water and enters the air.
Rose de France
Rose de France is a much lighter shade of purple Amethyst, more lavender or lilac. It has become very desirable in recent times.
Talisman
A talisman is an object, typically an inscribed ring or stone, that is thought to have magic powers and to bring good luck.
The Breastplate of Aaron
According to the Book of Exodus, this is The Priestly Breastplate worn by the High Priest of the Israelites. Sometimes called the Breastplate of Judgement. The breastplate contained four rows of three stones. One stone for each of Jacobs (Israels) twelve sons, set in their order of birth. Because Hebrew is a right to left script, the stones were probably ordered the same way on the breastplate.
Thermal Conductivity
The thermal conductivity of a material is a measure of its ability to conduct heat.
Trace Elements
A trace element is simply a chemical element that is present in an object, such as a gemstone, in a very low concentration (a trace amount). In gemstones, trace elements can alter the gemstone remarkably, such as changing its colour.

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