What is Gemmology?
Gemmology is the science of gemstones. GemExpert is confined to a scientific understanding of gemmology. This science is considered an interdisciplinary branch and has its roots in mineralogy, geology physics, chemistry and biology. Today gemmology is a renowned science with findings published in international journals (Journal of Gemmology, Gems&Gemology, Gemmologie).
Adding a name tag
Targets of gemmology are the identification of gemstones, the confirmation of authenticity, the evaluation of quality, the detection of origin, and the disclosure of treatment. First priority is the distinction between natural stones and synthetic counterparts and imitations. Whereas in the past the identification of synthetic crystals represented a major problem, today the difficult task is the identification of treatment. In most cases natural gemstones undergo artificial improvements. For this purpose the stones are subjected to different, mostly physical and chemical processes. As natural beauty is more rare than made up one, different prices apply to the two categories.
Origin is like a brand name
A special skill of gemmology is the identification of the geographical origin of stone. This is closely linked to the geological frame and origin. The host rock usually coins its formation, and the gemstone crystal contains a number of characteristics typical for its source. The consumers show a different appreciation for certain origin, as e.g. emeralds from Colombia, rubies from Burma or alexandrites from Russia. Such branded stones cost considerably more than similar gemstones from other localities. This branding requires an independent gemmological expertise from a renowned gemmological institute. The SSEF gemmological institute in Basel (www.ssef.ch) is worldwide a leading address for gemmological services.
Pearls and other organic materials
Organic products such as pearls, corals, amber and ivory possess a loose connection to gemstones. Pearl testing is a special task of gemstone identification. X-ray pictures and microtomography imaging is a standard procedure for pearl testing. High values are involved for natural pearls, and cultured pearls are safely separated from natural ones. Saltwater cultured pearls are luxury items compared to freshwater cultured pearls. Laboratory reports identify the different kinds.
Natural, synthetic, imitation: the main categories
The following nomenclature is a necessity when dealing with stones and jewellery. Natural stands for naturally grown in nature. "Synthetic" means grown after a natural model in a technical environment, e.g. synthetic ruby or synthetic diamond. Imitations are just look-likes as e.g. blue glass, polystyrene or zirconia.
Synthetic crystals have been produced since about 100 years. Meanwhile synthetic crystal have been produced in masses and used in the trade, as e.g. synthetic sapphire, synthetic ruby, synthetic spinel, diamond, alexandrite, emerald, amethyst or opal. Imitations exist since a very long time e.g. glass, mineral substitute as zircon for diamond, plastic. The most widespread imitation of diamond is zirconia (synthetic ZrO2), a material that is produced artificial not found in nature in this form, quality and quantity. At first sight a zirconia brilliant cannot be distinguished from diamond in the same shape.
Identification of gemstones: instruments are required
Mineral name and natural origin are the prior tasks of identification. The identification of a mineral species is possible with some low cost gemmological instruments. Refractive index, density and optical character represent the main data needed for the identification. Microscopic analysis of the internal features (inclusions), furnish fingerprints of authenticity (natural or synthetic) and often origin. This identification can be practised in simple steps by trained gemmologists in 95% of the cases. In a gemmological laboratory further scientific instruments are used to prove the authenticity or state a treatment. Analytical instruments may comprise FTIR (Fourier transform infra red spectrometry), EDXRF (energy dispersive x-ray fluorescence), Raman micro spectrometry, LIBS (Laser induced breakdown spectroscopy) and LA-ICPMS (laser induced inductively coupled plasma mass spectrometry).
Treatments lower the value
Natural beauty is required, but the majority of gemstones got an artificial make-up. Each gemstone variety has its own kind of treatments to improve quality. Improve the colour, increase transparency or hiding fractures are the most encountered gemstone treatments.
What is a gemmologist?
Gemmologists are experts in gemmology. They have a systematic knowledge of gemstones and are able to identify natural and synthetic stones and imitations by means of simple optical instruments. The quality of a gemmologist depends on his training and the actuality of his knowledge. The education in gemmology is often added to a first profession (jeweller, merchant, salesperson). National gemmological societies offer annual courses and release diplomas after due examination (FGA Gemmological Association of Great Britain; GG Gemmological Institute of America, etc.). Scientific gemmologist has a background in natural sciences topped by a gemmological education. If you want to know more about a gemmological education, go to www.ssef.ch for specific information.
Gemmologist may work in the central purchase of larger firms, in auction houses, or in individual laboratories. With respect of national or international comparisons only a few gemmological laboratories exist, that work on a high level: SSEF, Gübelin, GIA, HRD). Respected institutes are well equipped both with highly educated staff and scientific instrumentation and experience a long history free of scandals.
Appraisal, evaluation, price determination
The main interest of a potential gemstone owner or seller is the price of a stone or a jewel. Before a meaningful monetary evaluation can be made, the identity of the material and a judgement of the quality must be made. Only when this job is done decently, price estimation can be performed. A sole value for a piece of jewellery does not exist due to the different steps in the trade: replacement value, insurance value, retail value, wholesale value, or liquidation value. Gemmologists rarely are trained for determination of a value, but restrict on the material identification that is a scientific task and not a commercial task. They do not enter the field of commercial activities. Fraudulent estimations often related with individually operation gemmologists have lead to losses of millions, to the disadvantage of banks and investors.
The Diamonds: what is a brilliant
Diamond is mineral consisting of carbon crystallised in the cubic system. The material has a density of 3.52 g/cm3, a refractive index of 2.417, a hardness of 10, high temperature conductivity, perfect cleavage. The mineral appears in different colours, the best-known diamond is colourless to slightly yellowish. Fancy colours (yellow, green, brown, pink, red, blue and black) are very much in fashion and rarely available.
Diamond in the round brilliant cut (1 table, 32 crown facets, 24 pavilion facets, 1 optional culet) is the standard and called a brilliant. Other materials in the brilliant cut cannot be called "brilliant" without the mineral name just with the term brilliant. Diamonds can also be cut in different shapes and styles (octagonal step cut, marquise, drop, heart) and are then not termed "brilliant". Diamonds in more simple cuts like the Swiss cut, 8/8 cut or rose cut are - of course- not called brilliants.
Although diamond is the hardest mineral it is very sensible to pressure and blows. Already at 700 °C diamond gradually transforms in the presence of oxygen (air) into carbon dioxide. A diamond is thus not principally forever, but a very sensitive gem that needs a careful handling.
Synthetic diamond possesses all characteristic of diamond, but is produced as an industrial product, and is therefore much cheaper. An expert is able to distinguish between natural and synthetic diamond. Natural diamonds may have artificial colours! Treated diamonds are detected in experienced gemmological laboratories (e.g. SSEF).
Diamond imitations (e.g. zirconia) are sometimes misrepresented in the trade as synthetic diamonds.
Diamond identification and quality assessment: the 4C's
Diamonds are identified by their physical features before a quality grading is performed. Since some years not only diamond imitations are in the market, but synthetic diamonds, too. The separation is not always trivial but practicable for professionals. Natural diamonds still represent the bulk of the trade mass. The commercial value of cut diamonds depends closely from four main quality criteria, the 4C's:
Carat: how large?
Weight given in carats (1 ct = 200 mg, 5 carats = 1 gram)
Colour: how colourless?
Degree of colourlessness compared to comparison diamonds of an internationally recognised masterstone set ( D to Z). Diamonds with stronger saturations as Z are called "fancy coloured diamonds".
Clarity: how pure?
Degree of inclusions as judged after international standards
(loupe clean, VVS, VVS2, VS1, VS2, Si1, SI2, Piqué1, 2, 3)
Cut: how good quality of symmetry and polish after international standards?
(excellent, very good, good, medium, poor)
Diamonds should be accompaigned by an actual grading report of an internationally renowned laboratory, preferably GIA.