Harvesting of saltwater pearls in China extends back to 200 BC, but only in the last 30-40 years have cultured saltwater pearls been farmed there.Production is mostly from the Akoya pearl oyster Pinctada imbricata and is limited to the southern provinces of Guangxi, Guangdong, and Hainan, which have suitable water temperature.The first private saltwater cultured pearl farms were established in 1986.Production grew rapidly, and by 1995 it reached ~15 tons/year.Production subsequently reached ~20 tons/year, but recently it has decreased in both quality and quantity due to several factors (e.g., environmental degradation).This article provides details of the Chinese Akoya pearl culturing and farming processes, which have many similarities to those used in the production of freshwater cultured pearls.Unfortunately, the industry now faces a number of serious infrastructure and environmental challenges.The existing farms are aging, and there is little capital available for improvements in facilities or techniques.Efforts to increase production have caused overcrowding and a further reduction in the quality of the cultured pearls.JEC Conjuring blue magic.T. Redgrave, Readers Digest (New Zealand), Vol.158, No
It is difficult to determine the chronological age of fossil resins by chemical analysis alone, because amber samples of the same geologic age may have experienced different chemical reactions and temperatures during their fossilization.This study was undertaken to evaluate the possibility of classifying ambers by thermal analysis techniques.Thermal analysis involves the detection of small changes in the weight of a sample as it is subjected to controlled heating.Two methods-thermogravimetric (TG) and differential thermogravimetric (DTG) analyses-were used for 13 amber samples of various ages (present day to Triassic, 225 million years ago) and eight geographic origins.Using the DTG method, all samples exhibited a main weight-loss event at about 400°C, but the exact temperature varied according to age (i.e., the temperature increased linearly with age).The results suggest that thermal analysis provides an additional way to characterize fossil resins.
This article suggests new terminology to describe the banding of agates, in order to alleviate the confusion caused by previous descriptors that have no direct correlation to genetic implications.One ambiguous term, Uruguay banding, has been used to describe the straight parallel banding that often occurs in the lower portions of agate-containing vesicles from continental flood basalts.Confusion results because agates with this type of banding are called Uruguay agates, a term that some use to describe any agate from Uruguay.The author suggests using gravitational banding to refer to all agate textures caused by the force of gravity, which in this case applies to the deposition of relatively thick bands of coagulated silicic acid.The term adhesional banding is suggested as a replacement for terms such as concentric, common, normal, and fortification banding; these all refer to the thin layers of silica that adhere to the vesicle walls and form concentric rings or zones.Both types of banding commonly occur in agates formed in continental flood basalts from many locations worldwide.Several factors, including the amount and thickness of the lava flow, the temperature and humidity of the region, and the amount of CO 2 in the atmosphere, all contribute to the formation of the agate-filled vesicles.A suitable lava thickness will facilitate a slow cooling rate, which allows for the coalescence of numerous gas bubbles into larger vesicles and voids.Conversely, cooler atmospheric temperatures will inhibit vesicle formation.Sufficient rainfall will provide enough water for Gemological
Amber is a fossilized form of terpenoid plant resin, the sticky substance produced by plants all over the globe.Diterpenoid resins, produced by conifers and angiosperms, are prone to polymerization and are the predominant source of amber used for cultural purposes (including gems).Triterpenoid resins, produced by broad-leaved trees, are nonpolymerizing and used as varnish resins or for incense.This study applied solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy to several hundred samples in order to characterize modern resins, fossil resins of known geological provenance, and archeological materials.Diterpenoid and triterpenoid samples were distinguished on the basis of their 13 C NMR spectra, as were changes in spectra according to age, presumably as a result of polymerization or degradation.Four major groupings of fossil resins were recognized.Group A resins spanned the globe in Cretaceous time and relate to the modern genus Agathis in New Zealand and Australia.Group B resins were widespread in Tertiary times from India to North America but are not related to specific modern plants.Group C resins, the Baltic amber group, were localized in Europe in Tertiary time but do not correspond to modern genera.Group D resins are found in the Americas and Africa and are closely related to the modern genus Hymenaea.Thus, 13 C NMR spectra can be used to determine the general provenance of archeological materials provided a sufficient sample (>30 mg) and an extensive NMR spectra database are available.
The diamond, colored stone, and pearl businesses have witnessed unprecedented change since the turn of the 21st century.Not only have new markets for gems emerged around the world, but channels of distribution have also changed dramatically as a result of economic forces and political pressures.De Beers abandoned its single-channel seller role, which created-for the first time in over a century-a competitive rough diamond market.Political problems in Madagascar and a ban on gem exports from Myanmar disrupted supply channels for sapphire and ruby.And the proliferation of new sales avenues, through the Internet and TV, has given consumers much more information about gems and forever changed the way they buy them.The use of gems to subsidize bloody conflicts and repressive regimes has moved the trades to become more accountable, as concerns over terrorism and illicit trading have created a new legal environment.At the same time, a new class of consumers who value ethically, socially, and environmentally friendly products are making their demands known in the gemstone business.
A new model is proposed for the formation of opal showing play-of-color, as well as potch (common opal).According to this new model, the essential requirements for opal formation are: (1) artesian "mound" springs with alkaline, silica-rich waters; (2) a mechanism for changing the physicochemical features of this water so that suitable silica spheres are precipitated in linear chains; and (3) the occurrence of suitable voids lined with clay-which acts as a semipermeable membrane to concentrate and purify the silica solution by ultrafiltration and dialysis.Active and extinct artesian mound springs are found in general proximity to several sedimentary rock-hosted opal fields in New South Wales, South Australia, and Queensland.In the Great Artesian Basin, the natural springs lie on a NEtrending line over 300 km long, subparallel to the Lightning Ridge opal fields.The lepispheres in play-of-color opal are very uniform in size (apparently within 2-3% of the mean size), indicating a batch process rather than a continuous one.The mixing of the high-pH spring water with cool, slightly acidic groundwater that has low total dissolved salts would decrease the pH, lower the temperature, and lower the ionic strength of the spring water; all three processes facilitate the formation of silica spheres.Montmorillonite (clay) can act as a semipermeable membrane and assist in the pressurization of the fluids for ultrafiltration.
This article addresses three issues: Why is jadeite not transparent?Why is most jadeite green?Why is the chemical composition not always constant?The answer to the first question is the polycrystalline structure of jadeite: Light is scattered at the grain boundaries.The transparency of the stone is essentially influenced by the size and homogeneity of the grains, and can be clearly enhanced by filling of the pores.The answer to the other two questions can be found in the fact that jadeite, NaAlSi 2 O 6 , forms a solid-solution series with kosmochlor, NaCrSi 2 O 6 .Isomorphic replacement of Al by Cr in jadeite correlates with increasing green color.Jadeite also forms a solution series with omphacite, a Ca-and Fe-bearing clinopyroxene.Variations in jadeite composition are due to isomorphic replacement by kosmochlor and omphacite components.A new standard introduced in Hong Kong allows for small amounts of these impurities in jadeite, as long as a specific gravity of 3.4 and a refractive index of 1.688 are not exceeded.This type of jadeite is called Fei Cui in China. RTThe geochemistry of gem opals as evidence of their origin.
Mozui, which means "black jadeite" in Chinese, is mined in Myanmar and southern China.Recently, it has become common in Asian jade markets.It is essentially monomineralic, consisting of >90% omphacite, which is a pyroxene (like jadeite).This article reports on the gemological and mineralogical properties of this blackish green to black material and provides a comparison to jadeite.The refractive indices (1.667-1.670)and specific gravity (3.34-3.44) of "black jadeite" are almost identical to those of jadeite.It has a strong vitreous luster, and polished stones have a smooth surface.Petrographic studies show that the omphacite occurs as prisms or fibers of varying length; the grain size is usually <0.3 mm.Albite, tremolite, and some minute opaque grains with metallic luster are minor constituents.Only subtle differences are found in the infrared absorption spectra and Xray powder diffraction patterns of the two materials.The chemical formula of the omphacite in "black jadeite" is (Ca,Na)(Mg,Fe 2+ ,Fe 3+ ,Al)(Si 2 O 6 ); the ratio Na/(Na+Ca) is 0.45, which lies between that of jadeite (>0.8) and diopside (<0.2).The main trace elements are Sr, Cr, and Mn.Even though there is a clear difference in the chemical compositions of the main pyroxene minerals in "black jadeite" (omphacite) and jadeite, the authors suggest that the black material should nevertheless be considered jadeite, since their physical properties are almost same.Yet, they acknowledge resistance to this suggestion; the name "omphacite jade"
The degree of crystallinity (i.e., crystallite size) of agates from 11 locations on five continents was determined by powder Xray diffraction analysis.These agates formed within vesicles (gas cavities) in volcanic rocks; the ages of these rocks were obtained from the literature.The author found a strong correlation between agate crystallinity and age of the host rocks.Over geologic time, ageing allows the crystallite size to increase.Accordingly, the determination of agate crystallite size should allow an estimation of the approximate age of the host rock, which can be used to differentiate known agate deposits (since each has a unique age).The same correlation was deduced between agate density and age of the host rock.These conclusions have several potential applications.For example, an agate "artifact" purchased in Idar-Oberstein was shown most likely to have originated from Brazil rather than Germany on the basis of its degree of crystallinity and density.However, for this technique to become an accepted gemological tool, a large database with crystallinity and age data for volcanic agates and their associated host rocks, from many localities worldwide, must be developed.This method is not currently applicable to agates occurring in sedimentary rocks.KAM Bright prospects for pearl culture in India! A. K. Sonkar, Infofish International, January 2003, pp.13-16
Raman spectra were obtained from natural-and treated-color (i.e., dyed and irradiated) Chinese freshwater cultured pearls, as well as Tahitian cultured pearls.The spectra were useful in identifying the dyed cultured pearls, but not the irradiated cultured pearls.Chemical analyses (by atomic absorption for 16 elements) of four of the Chinese samples (white, orange, purple, and dyed dark purple) showed no characteristic variations.Compared to the Chinese samples, chemical analysis of one Tahitian cultured pearl showed a distinctly lower Mn content (1 ppm vs. 241-643 ppm) and possibly elevated contents of Na, Sr, and Fe.WMM
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