Stefanos Karampelas

Role of polyenes in the coloration of cultured freshwater pearls

The exact nature of pigments present in cultured freshwater pearls is still not well known. We examined 21 untreated cultured freshwater pearls from Hyriopsis of typical colors by diffuse reflectance UV-Vis-NIR and Raman scattering measurements, at high resolution. The objective was to establish the relation between color and the nature of the pigment mixture in pearls, using strictly non-destructive methods. All natural color samples show the two major Raman resonance features of unmethylated (unsubstituted) polyenes, not carotenoids. Their general chemical formulae are R-(-CH=CH) N -R′ with N = 6 to 14 and they give absorptions from violet to yellow–green. Each color is due to a mixture of pigments, not a single pigment. Different colors are explained by different mixtures. Each pigment identified by Raman spectroscopy can be related to a specific absorption with apparent maximum in the range 405–568 nm, thus absorbing from violet to yellow–green. This is the first study of the precise relation between Raman and diffuse reflectance spectra of cultured freshwater pearls.

Use of the Raman spectrometer in gemmological laboratories: Review

The current paper gives an overview of the development of Raman spectrometry in gemmological laboratories. While before 1990s, no commercial gemmological laboratory possessed such an instrument, all larger international labs have acquired these instruments by now. The Raman spectrometer is routinely used for the detection of emerald fillers, HPHT treatment of diamonds, analysis of the nature of a gemstone, analysis of gemstone inclusions and treatments, and the characterisation of natural or colour enhanced pearls and corals. Future developments in gemstone research lie in the closer analysis of the features of Raman and PL spectra and in the combination of several instruments.

Identification of the Endangered Pink-to-Red Stylaster Corals by Raman Spectroscopy

RAPID COMMUNICATIONS GEMS & GEMOLOGY SPRING 2009 n June 2007, delegates from 171 countries convened at The Hague to decide which species to include under the CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) agreement. The aim of CITES is to ensure that international trade in plant and animal specimens does not threaten their survival. The species covered by the convention are listed in three appendices, according to the degree of protection they need. Appendix I includes species threatened with extinction, where trade is permitted only in exceptional circumstances. Species in Appendix II are not necessarily threatened with extinction, but their trade must be controlled to avoid use that would threaten their survival. Appendix III contains species that are protected in at least one country that has asked other CITES parties for assistance in controlling the trade. The gemological significance of this triennial meeting is that corals from the Corallium genus, the most important of all gem coral species, were being considered for protection under Appendix II (CITES, 2008a). Ultimately, it was decided not to include them. More recently, on April 8, 2008, China, which now has domestic laws to protect these species, requested that CITES include four Corallium species (C. elatius, C. japonicum, C. konjoi, and C. secundum) under Appendix III (Fish and Wildlife Service, 2008). Meanwhile, the Stylasteridae family, which includes all Stylaster gem corals (e.g., figure 1), remained listed under Appendix II of CITES (as of January 18, 1990), which means a certificate issued by the management authority from the country (or state) of export is required (CITES, 2008b). Pink-to-red corals have been used for ornamental purposes for about 10,000 years (Liverino, 1989). According to Rolandi et al. (2005), there are two classes, Hydrozoa and Anthozoa, within the Cnidaria phylum (i.e., cnidarians) that have skeletons durable enough for use in gem materials and carvings. These two classes each contain a family (Stylasteridae and Coralliidae, respectively) that together yield the majority of pink-to-red coral species used for ornamentation (Pienaar, 1981; Rolandi et al., 2005; Smith et al., 2007). Most corals found in the IDENTIFICATION OF THE ENDANGERED PINK-TO-RED STYLASTER CORALS BY RAMAN SPECTROSCOPY

Luminescence spectroscopy and microscopy applied to study gem materials: a case study of C centre containing diamonds

The methods of luminescence spectroscopy and microscopy are widely used for the analysis of gem materials. This paper gives an overview of the most important applications of the analysis of laser and UV excited luminescence by spectroscopy and visually by microscopy with emphasis on diamond, and specifically natural type Ib diamond, little studied so far. Luminescence based techniques are paramount to the gemmological analysis of diamond, in order to determine whether it is natural, treated or synthetic. The great sensitivity of luminescence helps detect some emitting centres that are undetectable by any other analytical method. Hence, especially for diamond, luminescence is an enabling technology, as illustrated by its pioneering use of imagery for the separation of natural and synthetic diamond, and of spectroscopy for the detection of High Pressure–High Temperature treatment. For all other gemstones the applications are at the moment less numerous, but nevertheless they remain highly important. They provide quickly information on the identification of a gem material, and its treatment. Besides the study of broad band emissions caused by various colour centres, the typical PL-causing trace elements (amongst others) are chromium, manganese, uranium and rare earth elements. In pearls the study of broad band luminescence can be useful, and particularly the study of pink to red porphyrin luminescence in pearls from certain species such as Pinctada and Pteria and others can help identify the pearl-producing mollusc, or if a pearl has been dyed or not. Type Ib diamonds are representative of the importance and complexity of the analysis of luminescence by microscopy and spectroscopy. They show a wide range of sometimes very complex emissions that result in luminescence colours from green to yellow to orange or red. These emissions show generally very inhomogeneous distribution. They are caused by a range of defects, however only a few of them are well characterized.

Blue Sapphires from the Baw Mar Mine in Mogok

In the last five years, fine Burmese blue sapphires from the Baw Mar area of Mogok have reached the market. The faceted stones typically show a strong pleochroism from greenish to violetish blue when viewed perpendicular and parallel to the c-axis, respectively, with medium to strong saturation and medium to dark tone. Most of the samples were relatively clean under the microscope, showing multiple twinning with whitish needle-like inclusions (presumably boehmite) at the intersections. Often, these inclusions were associated with stress tension fissures. Needles, most likely rutile, were found only occasionally, but small platelets and needle-like particles, probably ilmenite, appeared more frequently. Most of the stones contained surface-reaching open and healed fissures, but crystal inclusions of K-feldspar and mica (identified by Raman) were occasionally encountered. The sapphires also had a relatively high iron content, low gallium, and very low titanium. Their Ga/Mg ratio varied from 0.6 to 17. Their UV-VisNIR spectra displayed intense iron-related absorptions, and the FTIR absorption spectra presented mainly boehmiteand mica-related bands. Based on careful microscopic observations, combined with spectroscopic and chemical analysis, the sapphire from Baw Mar can, in most cases, be distinguished from the blue sapphire of other localities.

A Study of the Gems in a Ciborium from Einsiedeln Abbey

GEMS & GEMOLOGY WINTER 2010 Agroup of four sacred objects belonging to the treasury of Einsiedeln Abbey, an important Benedictine monastery in Einsiedeln, Switzerland, were recently loaned to the Swiss National Museum in Affoltern am Albis, for identification of the materials used in their construction. This article presents the results of the investigation of the oldest object, a late-16th-century ciborium (a container for storing the consecrated host from a Mass; figure 1). Einsiedeln Abbey dates from the 10th century. It is dedicated to Our Lady of the Hermits and is a destination on a major Roman Catholic pilgrimage, the Way of Saint James. The ciborium was crafted by Nikolaus Wickart, an established goldsmith, in Zug about 1592. Its construction cost 300 krones (equivalent to 975 g of gold), paid for by donations from Maximilian III of Habsburg and numerous other contributors. The main body of the ciborium depicts the 12 apostles of Jesus Christ, while the lid illustrates the passion of Christ and is where the Christogram IHS is engraved. On the underside of the ciborium, there are several stamps, including those of Maximilian III, Wickart, and Einsiedeln Abbey. For more information regarding the history of the ciborium, as well as a stylistic and iconographic description, see Distelberger and Lanz (2009). The ciborium could not be removed from the Swiss National Museum laboratory for security reasons; thus, all testing took place there. The results were compared with the observations made by Father Eustache Tonassini from 1794 to 1798, during the documentation of the treasures of Einsiedeln Abbey (figure 2). Father Tonassini mentioned that all the stones and the gold had an “oriental” origin.

Spectral Characteristics of Natural-Color Saltwater Cultured Pearls from Pinctada Maxima

GEMS & GEMOLOGY FALL 2012 193 S cultured pearls from Pinctada maxima are farmed primarily in Australia, as well as in Indonesia, the Philippines, Myanmar, and other localities (see Shigley et al., 2010, and references therein). Marketed as “South Sea” cultured pearls, they are usually bead-nucleated and can reach large sizes (sometimes >20 mm). The colors commonly found in the market range from white to light gray (“silver”) to “cream” to yellow and “golden” (Elen, 2001, 2002b; Mamangkey et al., 2010; Shigley et al., 2010, and references therein). Less commonly, they may show pinkish, purplish, reddish, or brown bodycolors with various overtones (see figure 1 and photos in table 1). The darker SWCPs from P. maxima sometimes appear similar to lighter-colored SWCPs from Pinctada margaritifera and Pteria sterna. The spectral characteristics of yellow to “golden” natural-color SWCPs from P. maxima have been documented previously (Elen, 2001, 2002b; Mamangkey et al., 2010). This article presents a diffuse-reflectance and photoluminescence spectroscopic study of natural-color SWCPs from P. maxima in an effort to characterize their coloration mechanisms. A better understanding of these mechanisms will help to identify the P. maximahost mollusk of South Sea cultured pearls and to separate natural-color samples from their artificially colored counterparts.

Variscite from Central Tajikistan: Prelminary Results

An occurrence of variscite containing strengite, as well as other minerals from both the variscite and metavariscite groups, was discovered in the late 1970s in central Tajikistan. The material, ranging from light blue to light green to green, is suitable for cabochon cutting. The samples presented in this study showed traces of sulfur and arsenic, with higher iron and generally lower vanadium and chromium concentrations than variscites reported from other localities.These differences may result from the intergrowth of variscite with other minerals from the variscite and metavariscite groups.

Chapter 10:Gemstones and Minerals

Improvement of gem materials, imitations as well as growing of synthetic gems has been known for a long time, e.g. ancient Egyptians were heating agate to give a more attractive color,1 and Plinius the Elder listed several recipes of how to treat gemstones already as early as 77–79 AD. Moreover, “so...