gems, corundum, Madagascar.12, inclusions

A look at sapphire in southern Madagascar, including a description of its inclusions.

gems, corundum, inclusions.5

In a new series for Gems&Jewellery magazine, Bangkok-based gem testing lab Lotus Gemology delves into its photomicrograph archive, Hyperion, to help gemmologists tackle tricky inclusions. In this inaugural column, we discover the difference between crystal types in ruby and sapphire.

gems, corundum, inclusions.5, Burma.12

In the third of a four part series for Gems&Jewellery, Bangkok-based gem testing lab, Lotus Gemology, shares pairs of photographs that, when placed side-by-side, reveal the full story of an inclusion or treatment. In this issue, we explore how inclusions can help to reveal the origin of rubies...

gems, corundum, sapphire, inclusions.5, Madagascar.12

Growth tubes are a typical inclusion in corundum and often seen during examination in the laboratory. While commonplace, a stunning cluster such as the one seen above calls out to the photomicrographer. At the surface these tubes are cut through and some black debris has become lodged inside the ends, while deeper within the stone they still display a fiery glow, reminiscent of rockets launching into the sky. Not only do these tubes spark the imagination, but they can actually tell us a lot about the identity of their sapphire host. The limonitic staining found deeper in the tubes is a yellowish orange, suggesting that they have not been altered by heat treatment. These stains often turn a darker reddish or brownish color in heat-treated stones (J.I. Koivula, “Useful visual clue indicating corundum heat treatment,” Fall 2013 G&G, pp. 160–161). Furthermore, we have observed in the past several months that these prominent growth tubes are a common feature in Madagascar sapphire. While the tubes can be found in corundum from other origins, they seem particularly common in the Madagascar material that has been entering the Bangkok market in greater numbers recently. When taken into account along with other features, they provide a clue to the origin of these sapphires. Thus, what initially appeared to be a mundane inclusion is both visually impressive and gemologically significant, as it provides hints to the origins and treatments of corundum.

gems, corundum, sapphire, Burma.12

Gems are renowned for their outward beauty, but their in-ternal world can be just as striking. Lotus Gemology re-cently came across a Burmese sapphire, cut as a cabochon and measuring 8.92 × 7.10 × 4.75 mm, that displayed a six-rayed star. Once we examined it under the microscope, we were surprised to find that this celestial theme carried through to the inclusion scene inside (figure 13).

corundum, History.1, Chemistry.2, properties.3, color.4, inclusions.5, treatments.6, synthetic corundum.7, assembled stones.8, fashioning.9, quality.10, geology.11, sources.12, Australia.12, Afghanistan.12, China.12, India.12, France.12, Laos.12, Madagascar.12, Mozambique.12, Malawi.12, Myanmar.12, Pakistan.12, Sri Lanka.12, Tanzania.12, Tajikistan.12, Thailand.12, Vietnam.12, USA.12, Montana.12, gems, irradiation paper on ruby, Indian lapidary, color science, Kashmir, Mogok

From the dawn of time, ruby and sapphire have both attracted and fascinated humans in ways that few other items could. While objects of desire are found throughout the natural world, physical beauty is too often ephemeral. From the allure of a man, woman, flower or butterfly, through the fleeting moments of a sunset, there is little that lasts and practically nothing that can be passed down to our descendants. The exception is precious stones. Not only are they the most durable creations of mother nature, but their visual splendor is truly eternal. In this companion to his 2013 book, Ruby & Sapphire—A Collector’s Guide, Richard Hughes examines these gems from the gemological standpoint, delving into them not just from the aesthetic, but also from the scientific point of view. The product of nearly 40 years of firsthand experience, this book covers the subject from A–Z. History, sources, prices, quality analysis, causes of color, geology, synthetics and treatments—everything is here. Ruby & Sapphire—A Gemologist’s Guide arguably represents the most comprehensive volume ever written on a single precious stone. With over 1000 photos, maps and illustrations and 3500 references, it is nothing less than a tour de force of gemological scholarship.

gems, corundum, color.4, treatments.6, UV fluorescence

Hughes and Emmett examine ultraviolet fluorescence as a practical gemological tool for investigating the heat treatment of ruby and sapphire, particularly the relationship between fluorescence and the temperatures experienced by corundum. Heating can alter or destroy mineral inclusions and other microscopic evidence traditionally used to recognize treatment, but it can also produce systematic changes in fluorescence related to the behavior of trace elements and defects within the crystal. The authors discuss how fluorescence reactions under ultraviolet illumination can provide clues to treatment history and help distinguish corundum subjected to different thermal conditions. Particular attention is given to the scientific basis of these reactions and their practical observation, demonstrating how a simple and long-established gemological technique can yield valuable information when interpreted in conjunction with other evidence. Italian translation of the article “Heat Seeker: UV fluorescence as a gemological tool”

gems, gem testing, gemology, instruments, spectrophotometers, Raman

corundum, geology.11, Madagascar.12, gems

2 Sept. 2015 (updated 28 Sept. 2015) – Recently, a close friend of ours gave us a heads-up about a new ruby mine in Madagascar, sending a photo that showed several pieces of gemmy blood-red ruby rough sitting atop a small scale. Word had it that the Madagascar bush had yielded up yet another piece of crystallized treasure, this twist on terra firma in the form of blood-red ruby. Today rumor became reality. A client walked in with a few dozen faceted rubies. As always, we asked for the source. Mozambique" was the reply. Ho hum. Until I scoped the first piece.Have you ever met someone briefly, and then, after a long period, you glance at a face and think to yourself: "Something's familiar. I think I know you from somewhere." Gazing into the microscope brought back vivid memories of an epic 2005 visit to Moramanga, aka "Sierra Leone," a mine deep in the Madagascar bush. Yes, we had met before."

corundum, color.4, gems, color science

While virtually all gemological texts cover pleochroism, it is almost always related to viewing with a dichroscope; exactly how pleochroism manifests itself in faceted gems is largely ignored. This article discusses this phenomenon in doubly refractive gemstones, specifically as it relates to overall color appearance in faceted gems. Contrary to popular belief, pleochroism can be visible in faceted gems even when they are cut with an optic axis parallel to the direction of view.