Missing Gaps in Gemmological Terminology?
This article does not intend to set standards or correct any existing article or gemmological text. Standards already exist, namely those of CIBJO, The World Jewellery Confederation that may be downloaded for free here. This brief overeview has resulted from the careful reading of multiple books and journals in the course of a normal study processes and peer review editing when it came to verify or validate written information. More than pointing out apparent mistakes or erroneous information, this approach has showed that there is a balance between the purist or scientific lexicon and the more trade orientated nomenclature, that is characteristic of gemmology that serves an industry that offers products to consumers. It also demonstrates that there are terms that emerge from colloquial tradition and not necessarily from the academia.
For this article, a selected number of situations have been chosen to illustrate the misuse of expressions and names, although in some cases, tradition wins over picky nomenclature. Under discussion here we have flame fusion synthetic spinels, marcasite, organic gems, alexandrite lore and Retzius lines. These are “alternative facts” in the sense that, for the more conservative and orthodox reader, they can be considered “fake news”.
Flame Fusion Synthetic Spinel
One of the most popular artificial products that gemmologists learn how to identify during their education is the flame fusion, or Verneuil, synthetic spinel. These have been around for almost a century and were produced in many colours (except red) to imitate, not natural spinel, but rather other gem materials such as the diamond, aquamarine or blue sapphire just to name a few (O’Donoghue, 2005). All the gem and jewellery community and almost all the literature simply describe these products as “synthetic spinel” (O’Donoghue, 2006, Matlins, 2003, Liddicoat, 1993, Hodgkinson, 2015).
In the photo. Mid-20th century gold brooch, made in northern Portugal, set with a flame fusion synthetic spinel © Carlos Pombo Monteiro, Fundação Eugénio de Almeida/Arquidiocese de Évora
The trade, however, has a very strict definition “synthetic” and CIBJO - The World Jewellery Confederation defines a synthetic stones as “artificial products having essentially the same chemical composition, physical properties and structure as that of their naturally occurring counterparts ” (CIBJO Gemstone Book, 2018). It happens that every gemmologist knows that the gemmological properties of natural spinel differ slightly from the properties of the flame fusion counterpart, much to the fact that they do not have the same chemical composition, with a different alumina to magnesia ratio (Al2O3 / MgO), that is 1-1 in natural spinel and usually 3.6-1 in the flame fusion product (Rinaudo, 1997). In strict observation of the CIBJO rules, we could not call these products as “synthetic spinels” as these do not meet the criteria for a synthetic stone. This is, however, a typical case when a verbal or written tradition overtakes the formality of a nomenclature rule. Despite the non-compliance with the trade standards, it is widely accepted and tolerated that these products can be named, tagged and traded as “synthetic spinel”.
Marcasite as Gem Material
In the gemmological world we call marcasite to an opaque, metallic lustre, golden material often cut in very small and simple rose-type pieces. Its first record in goes back to the 18th century (Pouget, 1762) with its heyday as a gem material in the 1930s (Bartlett, 1997). The name marcasite drives from the Arabic or Moorish word used to describe pyrite and other minerals (Anthony, 1990).
As an actual fact, the name of this stone shouldn’t be marcasite, but rather the name of the well-known cubic iron sulphide (FeS2): pyrite. Today, every major textbook acknowledges the fact that the material is pyrite and that marcasite is an accepted trade name in the jewellery community (Webster, 1994, Hodgkinson, 2015) although it hasn’t been listed in the CIBJO Gemstone Book annex with the list of gemstone names (CIBJO Gemstone Book, 2018).
Marcasite is in fact the IMA - International Mineralogical Association’s approved name of a distinct mineral that has no use in jewellery whatsoever, causing sometimes confusion to a more scientifically educated public. Marcasite and pyrite are two distinct materials in spite of being polymorphs of iron sulphide, with marcasite crystallising in the orthorhombic system and pyrite in the cubic system (Klein, 1993). These polymorphs were defined as separate mineral species in 1845 when marcasite was proposed as a new species (Heidiger, 1845) but some authors and museums reportedly had difficulty in separating them (Bannister, 1932), a task that was greatly solved by Bragg in 1914 with the introduction of X-ray diffraction into mineral identification. In the jewellery world, the word marcasite continued to be used in the traditional way despite the acknowledgment of its true mineral classification as pyrite (Bartlett, 1997) and this is another typical case of an erroneous name that was kept and eventually accepted due to trade tradition.
In the photo: A ca. 1940s silver pin set with a paste and rose-cut marcasites
© Carlos Pombo Monteiro, Fundação Eugénio de Almeida/Arquidiocese de Évora
"Organic" Gems
Since the dawn of gemmological education in the second quarter of the 20th century that gem materials have been organised in such a way that it is common to separate categories like diamonds, coloured gemstones and organics. In the organics we can see a list of gem materials that originated from the activity of living organisms, e.g. ivory, bone, coral, tortoise shell, pearl, mother-of-pearl, shell, horn, corozo (vegetable ivory) and copal just to name the most important ones (Pedersen, 2004). It happens though that the word “organic” may has specific meanings rather than a broader statement of material that was generated in a living organism (e.g. a carbon based compound) and some scholars recognise that boundaries of the definition are somewhat arbitrary (Spencer, 2004). Moreover, some of the gem materials grouped as organics are not, in any sense, organic in composition and that is the case of precious corals, pearls, cultured pearls, mother-of-pearl and shell. The major composition of the materials is biomineralized calcium carbonate in aragonitic and/or calcitic structures (Strack, 2006) and carbonates, as crystal matter, are strictly speaking considered inorganic matter, not organic.
In the 2016 CIBJO Congress, these arguments were discussed and there was a consensus that the better word to describe those gem materials that originate from living organisms was “biogenic”, literally meaning that they result from biological activity. It may take some time to the trade and gemmological community to assimilate these concepts and to possibly embrace this new more accurate approach to the biogenic gem material’s nomenclature. Or we will witness the conservative approach to maintain the wording tradition as is the case of synthetic spinel and marcasite?
in the photo: The Viviane Strand by Paspaley, featuring 26 fine South Sea cultured pearls that are considered biogenic gem materials © Paspaley
Alexandrite colours
Alexandrite is the famous colour-changing variety of chrysoberyl that was first found in the Takovaya river, east of Yekaterinburg in the Ural mountains (O’Donoghue, 2006). It was called alexandrite in honour of the czarevitch Alexander Nikolayevich (1818-1881), the future Czar Alexander II, as the publication of its discovery is traditionally said to have been made on the day he was celebrating his coming of age in 1834, despite the fact that the first records on the material go back to 1833 (Schmetzer, 2010), suggesting that the discovery was in fact made in 1833. Some sources still quote erroneously 1830 or 1831 as the year of discovery, but that would not be consistent with an appropriate age to celebrate majority that, in Imperial Russia, was at the age of 16, not 13 or 14.
The typical colours of this gemstone, depending on quality, are pink to ruby red in incandescent light and bluish green in day light or day light equivalent. Only the higher quality chromium rich alexandrites display a dramatic ruby red to bluish green colour change (Proctor, 1988).
In more than one published source, it is said that the popularity of alexandrite among the Russians was linked to the fact that those colours, red and green, where the colours of imperial Russia (Smith, 1912). Neither the imperial Russian nor the Romanov’s heraldic representations have these colours combined (Russian colours are white, blue and red and Romanov colours are yellow and white), therefore there is no support for the allegation. Green and red are, however, the colours of the uniforms of the infantry military and some early authors have mentioned that because of that, the gem gained great popularity in the country (Bauer, 1904, Streeter, 1898). The “national” colour argument and a wrong 1830-1 year of discovery are typical cases of a distracted consultation of sources, miss quotation and not cross checking with original data.
In the photo: fine Russian alexandrite displaying the incandescent (red) and day light (green) colour change © Tino Hammid
Retzius lines
Ivory, an ancient material in human History, has been obtained from mammals whose teeth and/or tusks have size and properties suitable for use in decorative artefacts (e.g. elephant, hippopotamus, walrus, wart hog, sperm whale, killer whale, narwhal). Fossil ivory from pre-glaciation species, like the mammoth (Mammuthus primigenus), is also a source. Elephant ivory has been the most sought after, especially in African species (Loxodonta africana and Loxodonta cyclotis), but males of Asian species (Elephas spp.) also produce workable ivory (Pedersen, 2004). Depending on the species and country, these animals are protected and listed in the Appendix I and II of CITES, the Convention on International Trade in Endangered Species of Wild Fauna and Flora (www.cites.org).
The two modified upper incisors of elephants and mammoths have canicular-like growth linear structures with a typical cross section pattern that are important in the visual identification of ivory (Pedersen, 2004) and specialists now call them Schreger lines (Spinoza, 1991). In some cases, the close observation of these intersecting lines with an engine-turned decussating appearance enable the separation between elephant ivory and much older mammoth ivory (Penniman, 1952, Spinoza, 1991). In early gemmological education manuals, however, these lines are called “Retzius lines” or “lines of Retzius” (Read, 1988, Webster, 1975), an allusion to Professor A. Retzius of Stockholm University a known researcher on the study of the structure and development of teeth in the late 1830’s (Müller, J., 1842). It appears however that a researcher named Bernard Schreger was the first to describe the engine-turning pattern in proboscidean tusks back in 1800, a few decades before Retzius (Schreger, 1800). Hence the preference for the nomenclature.
Photo © Priv Coll.
Edited and extended from Galopim de Carvalho, Rui (2018), Getting Your Facts Right, Gems & Jewellery, Vol. 17,no. 1, pp. 28-29
References
Anthony, J., et al., 2003. Handbook of Mineralogy. Vol. I. Mineralogical Society of America, Chantilly, VA
Bannister, F. A., 1932. The Distinction of Pyrite from Marcasite in Nodular Growths. Mineralogical Magazine, 23,179-187
Bartlett, L., 1997. Fool’s gold? The use of marcasite and pyrite from ancient times. The Journal of Gemmology, 25(8), 517-531
Bauer, M., 1904. Precious Stones. Fac simile. Dover Publications. New York, 1968
CIBJO Gemstone Book, 2016. CIBJO - The World Jewellery Confederation. www.cibjo.org/introduction-to-the-blue-books/
Haidinger, W., 1845. Handbuch der Bestimmenden Mineralogie. Braumüller and Seidel, Wien, p. 559
Hodgkinson, A. 2015. Gem Testing Techniques. Valerie Hodgkinson. Scotland
Klein, C., Hulburt, C., 1993. Manual of Mineralogy (after J. D. Dana). 21st Ed. John Wiley & Sons. New York
Liddicoat, R. T., 1993. Handbook of Gem Identification. Gemological Institute of America. Santa Monica, CA
Matlins, A., 2003. Gem Identification Made Easy. 3rd Ed. Gemstone Press. Woodstock, Vermont
Müller, J., 1842. Elements of Physiology, Vol. II. Taylor and Walton, London
O’Donoghue, M., 2005. Artificial Gemstones. NAG Press. London
O’Donoghue, M., 2006. Gems. 6th Ed. Butterwhorth-Heinemann. Oxford
Pedersen, M. C., 2004. Gem and Ornamental Materials of Organic Origin. Elsevier Butterworth-Heinemann. Oxford
Penniman, T. K., 1952. Pictures of Ivory and other Animal Teeth, Bone and Antler. Pitt Rivers Museum. University of Oxford.
Pouget, J-H. P., 1762. Traité des Pierres Précieuses. Paris
Proctor, K., 1988. Chrysoberyl and Alexandrite from the Pegmatite Districts of Minas Gerais, Brazil. Gems & Gemology, 24(1), 16-32
Read, P., 1998. Dictionary of Gemmology. Butterworth-Heinemann. Oxford
Rinaudo, C. and Trossarelli, C., 1997. Optical and X-ray topographic study of Verneuil-grown spinels. The Journal of Gemmology, 25(5), 331-339
Schmetzer, K., 2010. Russian Alexandrites. Scweizerbart Science Publishers. Stuttgard
Schreger, B. N. G., 1800. Beitrag zur Geschichte der Zähne. Beitrage für die Ergliederungkunst. 1, 1-7
Smith, H., 1912. Gem-Stones and their distinctive characters. Methuen & Co. Ltd. London
Spencer L., et al., 2004. Chemistry for Today: general, organic, and biochemistry. Thomson Brooks/Cole, p. 342.
Spinoza, E. O. et al., 1991. Identification Guide for Ivory and Ivory Substitutes. World Wildlife Foundation.
Strack, E., 2006. Pearls. Rühle-Diebener-Verlag. Stuttgard
Streeter, E., 1898. Precious Stones and Gems, Their History, Sources and Characteristics. George Bell & Sons. London
Webster, R., 1975. Gems, their sources, description and identification. 3rd Ed. Butterworths & Co., London
Webster, R., 1994. Gems, their sources, description and identification. 5th Ed. Butterworths-Heinemann, London