corundum, inclusions.5,Gems

In this last of this series on origin determination, Gübelin Gem Lab talks about “holistic” diagnosis of features that can differentiate gems coming from different sources but created under similar conditions.

corundum, inclusions.5, treatments.12, synthetic corundum.7, ruby, sapphire, Australia.12, Burma.12, Cambodia.12, China.12, Colombia.12, Greenland.12, India.12, Kashmir.12, Kenya.12, Malawi.12, Pakistan.12, Sri Lanka.12, Tanzania.12, Thailand.12, USA.12, Montana.12, tanzanite, spinel, gems, jade, jadeite, fei cui, nephrite

Photoatlas, Volume 2, the long-anticipated successor to Photoatlas, Volume 1, was released in December, 2005. It covers gems other than diamonds, rubies, sapphires, and emeralds, which are covered in Volume 3. Like Photoatlas, Volume 1, which was first published in 1986, the second volume in the series will become a standard reference in the field of gemology. Once again, Dr. Eduard J. Gübelin and John I. Koivula have collaborated to produce an impressive pictorial atlas of gemstone inclusions. Renowned for their unique ability in capturing the beauty of the internal world of gemstones and bringing an artistic sensibility to a scientific subject in their photomicrographs, Dr. Gübelin and Mr. Koivula bring to Photoatlas, Volume 2 their considerable expertise and combined experience in laboratory gemology, mineralogy, geology and chemistry. The second volume in the Photoatlas series complements Photoatlas, Volume 1 with greater depth and scope, featuring inclusion specimens from localities discovered after 1986 and examples of treatment techniques and synthetics that have appeared in the gem market in the last two decades. Each chapter contains current information on the micro-characteristics of natural, synthetic and treated host materials along with a complete selection of photomicrographs and a suggested reference section. The Photoatlas suite is an indispensable resource for gemologists, mineralogists, collectors and jewelers.

corundum, inclusions.5, treatments.6, gems

jade, nephrite, China, Chinese jade, gems

It is a matter of great satisfaction and fulfillment for [HP] to have been given the opportunity to participate in this celebration of Michael Rogers. His influence has been uniquely important for me: quite simply, it was he who, initially and primarily, introduced me to the enterprise of historical work. Even more particularly, my subject relates to an area with which he has long been concerned, and concerning which we have long since had occasion to communicate. I hope that this present effort will find favor. As the present paper developed, it came to be much too large for inclusion in the planned volume in honor of Professor Rogers. When confronted with the necessity of radically reducing the size of my submission, I found only one viable course of action: that of cutting off and presenting the first part of the work I had written. The larger version naturally dealt with a broad, representative range of the types of pre-Timurid jade objects in the al-Sabah Collection and, in addition to the ancient objects here discussed, covered Islamic jades up through the fourteenth century. The necessary reduction of the present publication is made less painful by the project of a volume on pre-Timurid jades planned for publication by the al-Sabah Collection in the reasonably near future.

gems, corundum, inclusions.5, Brazil.12, beryl, emerald, inclusions,

This paper presents results of SEM and EDS study in some Brazilian gemstones. Emerald from Campos Verdes (GO) contains several mineral inclusions as talc, dolomite, chromite, pyrite, magnetite, etc. Sylvite crystals was firstly identified by SEM/EDS. These salt inclusions suggest percolation of K-bearing fluids during emerald crystallization. Emerald from Campos Verdes present higher concentration of Cr+3 in the outer green zones than in the inner colourless zones, showing that ion is a chromophore in this gemstone. SEM and EDS results combined with optical microscopy analyses demonstrate that amethyst from Rio Grande do Sul State (RS) contain needle-like inclusions of goethite and not cacoxenite and rutile as suggest by other workers. By these techniques it was possible to identify pyrolusite and hollandite as late minerals inside agate and quartz geodes from RS. SEM and EDS data of corundum from Barra Velha (SC) show that silk effect is produced by diaspore inclusions. These techniques also reveal that the asterism in this corundum is produced by empty needle-like channels instead of the presence rutile inclusions as commonly observed in other worldwide deposits. Rounded zircon inclusions are common in corundum from Indaiá, Palmeiras, Caputira and Campo Belo (MG). Sillimanite and/or kyanite inclusions in corundum crystals of secondary deposits from Indaiá suggest a metamorphic origin to this gemstone. Corundum from Caputira also contains several rounded rutile inclusions, which are diagnostic for this occurrence.

amber, Burma, gems

Amber (‘Burmite’) from the Hukawng Valley of Myanmar has been known since at least the 1st century AD. It is currently being produced from a hill known as Noije Bum, which was first documented as a source of amber in 1836. Several geologists visited the locality between 1892 and 1930. All of them believed that the host rocks to the amber are Tertiary (most said Eocene) in age, and this conclusion has been widely quoted in the literature. However, recent work indicates a Cretaceous age. Insect inclusions in amber are considered to be Turonian–Cenomanian, and a specimen of the ammonite Mortoniceras (of Middle–Upper Albian age) was discovered during the authors’ visit. Palynomorphs in samples collected by the authors suggest that the amber-bearing horizon is Upper Albian to Lower Cenomanian. The preponderance of the evidence suggests that both rocks and amber are most probably Upper Albian. This determination is significant for the study of insect evolution, indicating that the oldest known definitive ants have been identified in this amber [American Museum Novitates 3361 (2002) 72]. This site occurs within the Hukawng Basin, which is comprised of folded sedimentary (^ volcanic) rocks of Cretaceous and Cenozoic age. The mine exposes a variety of clastic sedimentary rocks, with thin limestone beds, and abundant carbonaceous material. The sediments were deposited in a nearshore marine environment, such as a bay or estuary. Amber is found in a fine clastic facies, principally as disk-shaped clasts, oriented parallel to bedding. A minority occurs as runnels (stalactite-shaped), with concentric layering caused by recurring flows of resin. An Upper Albian age is similar to that of Orbitolina limestones known from a number of locations in northern Myanmar. One of these, at Nam Sakhaw, 90 km southwest of Noije Bum, has also been a source of amber.

beryl, emerald, Colombia, Russia, Afghanistan, Brazil, synthetic beryl, emerald, gems

Since antiquity, emerald has been one of the most highly valuated gemstone: the first known mines were those of Cleopatra in ancient Egypt. Two thousand years ago Pliny wrote, Emerald-green is the most beautiful green of all." Leading researchers offer insight into many of the aspects of the world of emerald. -What is emerald? A portrait of a precious and unique member of the beryl family -How does emerald form? The events that conspired to bring about an unlikely outcome; -Where is emerald found? Worldwide localities including Canada, Namibia and China -Where are the richest deposits? Today's market sources: South America, Africa and Asia; -Is it possible to determine the origin of an emerald? Gemstone emerald: characteristics, inclusions and treatments;-What separates green beryl from emerald? The debate over optical, spectroscopic and chemical delineations; -How is emerald created in the lab and how can it be recognized? The history, process and detection of synthetic emerald; Plus etymology, history, legendary giants, local finds and more. extraLapis English No. 2, Emerald, provides a comprehensive look at this magnificent gemstone."

gems, corundum, USA.12, Montana.12, Rock Creek, Dry Cottonwood, Missouri River

Alluvial sapphires in southwestern Montana have supported a mining industry for over 100 years, yet the source rock for the sapphires has never been identified. This study uses geological mapping, trace element analysis and inclusion identification to characterize the Montana alluvial sapphires and extrapolate their origin. The placers occur in three areas in southwestern Montana: along the Missouri River, Rock Creek area, and Dry Cottonwood Creek. Detailed mapping of the placers has established that the present distribution is due to Quaternary reworking of Tertiary alluvium, indicating that the sapphires have been in the alluvial system for a minimum of 2 Ma and that the source area may be distant or completely eroded. Trace element analyses of the alluvial sapphires and a corundum reference suite were done using the proton microprobe. Corundum contains traces of Fe, Cr, Ti, V, and Ga, for which Ga displays significantly different patterns between alkali basalt and metamorphic corundum types. Ga in alkali basalt corundum is typically >100 ppm, with wide variation for samples within one deposit. Metamorphic corundum typically has Ga < 100 ppm, and tightly clustered distributions. The Montana alluvial sapphires have chemistry consistent with a metamorphic origin. The most common inclusions in alkali basalt corundum are ilmenite and hercynite. Metamorphic corundum hosts a wider variety of inclusions. The Montana alluvial sapphires contain plagioclase, muscovite, some clinozoisite, and rarely garnet. Using 'T-P' stability fields for these inclusions, the formation conditions for the Montana sapphires is estimated at 580 to 720°C and 9 to 13 kbar (~30 km depth), consistent with mid-crustal depths. The Bitterroot lobe of the Idaho batholith is proposed as the sapphire source area. It intruded into, and re-metamorphosed, metamorphic rocks of the Bitterroot Core Complex at mid-crustal levels. Exhumation by Cretaceous thrust faulting exposed these rocks at the surface by the early Tertiary, providing a 30-million-year window to erode sapphires into the Tertiary alluvial system. Quaternary reworking of the Tertiary gravel concentrated the sapphires into the present-day placers.Ga

gems, beryl, emerald, Egypt, Sikait, Austria, Habachtal, archaeology, geology, ancient gem trade, chemistry, oxygen isotopes

Examines the ancient exploitation and trade of emeralds from Austria and Upper Egypt through oxygen-isotope analysis and inclusion studies of archaeological and historical specimens. Giuliani and co-authors compare emeralds from the Habachtal deposit in Austria, the Ural Mountains, and Egyptian deposits at Zabara, Sikait and Umm Kabo with emeralds from Gallo-Roman and Egyptian jewellery. Oxygen-isotope ratios, supplemented where necessary by the petrography of fluid inclusions, provide distinctive signatures capable of separating the principal ancient sources. An emerald from a third-century AD earring in the Vaise Treasure at Lyon yields an isotopic composition characteristic of Habachtal, demonstrating that Austrian emeralds were being exploited by the Gallo-Roman period. Four emeralds from an Egyptian necklace in the Muséum National d’Histoire Naturelle have isotope values consistent with Upper Egyptian material, while nineteenth-century specimens collected from the Egyptian mines confirm the restricted isotopic range of those deposits. The study also reviews earlier analyses indicating Austrian origins for emeralds in the Visigothic Guarrazar crown and the medieval French crown, an Egyptian origin for other Roman-period stones, and a Pakistani source for an emerald from a Gallo-Roman earring at Méribel. The results support the historical reality of active emerald mining in both Upper Egypt and Austria during Roman times and demonstrate that emeralds from more distant Asian sources also reached the Roman world through long-distance trade routes.

gems, beryl, emerald, Colombia, geology, emerald formation

Emerald mineralisation in Colombia occurs in two separate zones along the margins of the Eastern Cordillera, approximately 80 km apart, with the western zone dated to around 35 million years ago and the eastern zone about 30 million years older. Crush-leach analysis of fluid inclusions in minerals such as emerald, quartz, calcite, dolomite, and fluorite from both zones reveals two distinct brine types associated with emerald formation, with many samples showing intermediate compositions. Fluid 1, primarily found in emerald-hosted inclusions, is dominated by NaCl and displays high Cl:Br ratios, indicating salinity from halite dissolution, likely sourced from local salt beds. Fluid 2, notably present in quartz-hosted inclusions, has similar salinity but contains lower Na and higher levels of Ca, K, Fe, and other cations, with lower Cl:Br ratios more typical of formation waters, though it also likely derives salinity in part from halite. Linear trends in bivariate plots of cation concentrations, regardless of host mineral or locality, confirm that mixing between the two fluids occurred. The presence of these same fluid types in both zones, despite differences in age and geography, suggests that fluid chemistry was controlled by similar interactions with evaporites and black shales in both cases. It is proposed that beryllium was transported as Be–F complexes in the NaCl-rich fluid and that emerald precipitated upon mixing with the calcic brine, which also triggered the precipitation of fluorite and parisite.