Gems & Gemology

Summer 2017 G&G: Russian Diamonds and PL Mapping of Synthetic Diamonds, Plus Sapphire Inclusions Chart

Jennifer-Lynn Archuleta
August 7, 2017
Summer 2017 Gems & Gemology
The lead article of this issue examines Russia’s Lomonosov mine, which is located in a Proterozoic zone in the Baltic Shield craton. Proterozoic tectonic processes are thought to be responsible for the fancy-color diamonds found at this source. The distinctive purplish pink melee diamonds on the cover are part of Lomonsov’s production. Photo by Robert Weldon/GIA, courtesy of Diarough.

The lead article of the Summer 2017 Gems & Gemology profiles Russia’s Lomonosov diamond deposit, Europe’s first diamond locality and a producer of fancy-color diamonds. Other diamond-related articles recount the characteristics and formation theories of carbonado and the use of photoluminescence mapping to identify optical centers, synthetic origin, and treatment. The Summer issue also features a wall chart showing inclusions in sapphire, as well as articles on establishing nephrite color determination standards, properties of Vietnamese tourmaline, and the sapphire deposits of Montana.

GEOLOGY AND DEVELOPMENT OF THE LOMONOSOV DEPOSIT, NORTHWESTERN RUSSIA

The Lomonosov deposit
The Lomonosov deposit produces a variety of fancy-color diamonds, including pink and purple diamonds. Similar to the pink diamonds from Argyle, these likely relate to their Proterozoic geologic setting, unlike many other deposits that occur in stable Archean regions. Photo by Kevin Schumacher.

While most Russian diamond mines are hosted by the Siberian craton, Lomonosov falls within the Baltic shield. Its Proterozoic geological setting location is likely responsible for its fancy pink diamond production. Authors Karen V. Smit and Russell Shor visited the Lomonosov deposit to tour the operations, processing, and sorting of Europe’s first diamond mine.

CARBONADO DIAMOND: A REVIEW OF PROPERTIES AND ORIGIN

carbonado diamond
The origin of carbonado diamond (far right) has yet to be definitively established. Uncovering their formation would represent a scientific breakthrough. Left to right: The 9.49 ct yellow diamond octahedron is a gift of the Oppenheimer Student Collection. The 109.47 ct diamond bort is a gift of Richard Vainer. The 118.01 ct carbonado, a gift of Stephen Haggerty, is from the Central African Republic. GIA Collection nos. 11953, 31602, and 40108. Photo by Robert Weldon/GIA.

This investigation into carbonado, a diamond aggregate with unusual textural features, proposes an extraterrestrial model for its genesis. Stephen Haggerty describes the known history, characteristics, and proposed origins for this remarkable material.

PHOTOLUMINESCENCE MAPPING OF OPTICAL DEFECTS IN HPHT SYNTHETIC DIAMOND

irradiated 1.06 ct Fancy Deep brownish orange HPHT-grown synthetic diamond
This irradiated 1.06 ct Fancy Deep brownish orange HPHT-grown synthetic diamond
of mixed type was examined in the study. Photo by Towfiq Ahmed.

Photoluminescence (PL) mapping is a viable method for separating natural, synthetic, and treated gem specimens. Lorne Loudin performs PL mapping on a synthetic diamond of mixed type and identifies optical defects incorporated into growth sectors, demonstrating the usefulness of this technique.

AN UPDATE ON TOURMALINE FROM LUC YEN, VIETNAM

7.1 ct green uvite tourmaline
The centerpiece of this ring is the 7.1 ct green uvite tourmaline from the secondary
deposit at Minh Tien. Photo by N.T.L. Quyen, courtesy of Nguyen Huy Truong.

Tourmaline has been from Vietnam’s Luc Yen district since the 1980s. A team of researchers led by Nguy Tuyet Nhung presents the characteristics of the tourmaline found in this gem-rich region, comparing the specimens with data from the literature.

CHARACTERIZATION OF MG AND FE CONTENTS IN NEPHRITE USING RAMAN SPECTROSCOPY

nephrite
The color varieties of nephrite. Photo courtesy of Beijing Boguan International Auction Co., Ltd.

Color determination of nephrite jade by visual observation can be problematic. Xiaoyan Feng and her coauthors propose a measurement based on nephrite’s Mg+2 and Fe+2 content to define boundaries between colors and to establish a standard for the highly sought fine white material.

INCLUSIONS IN NATURAL, SYNTHETIC, AND TREATED SAPPHIRE

Sapphires
Sapphires from a variety of sources. Faceted stones (left to right): 6.36 ct pink/orange (padparadscha), 1.63 ct pink, 4.76 ct violet, 5.43 ct violet purple, 3.03 ct blue, 2.12 ct blue, 8.06 ct yellow, 3.46 ct yellow, 2.00 ct orange, and 1.01 ct deep orange. Crystals (left to right): 9.88 ct pink, 17.80 ct violet, 30.07 ct purple, 42.13 ct blue, 10.84 ct yellow, and 5.86 ct yellow-orange. From the GIA Eduard J. Gübelin Collection and Bill Larson, Pala International. Photo by Robert Weldon/GIA.

The second wall chart in a series documenting common inclusions focuses on natural, synthetic, and treated sapphire. Inclusion specialists John Koivula, Nathan Renfro, Jonathan Muyal, and Shane McClure contributed photomicrographs to the reference chart.

BIG SKY COUNTRY SAPPHIRE: VISITING MONTANA’S ALLUVIAL DEPOSITS

bluish and greenish sapphires
Four of the best bluish and greenish sapphires mined from Eldorado Bar on the day of the authors’ visit. All four show the material’s characteristic pastel color, and some clearly display a hexagonal crystal habit even though the surface is worn. The second sapphire from the left, the largest recovered that day, weighs 16.78 ct. Photo by Kevin Schumacher.

Since the late nineteenth century, the western U.S. state of Montana has long been a source of alluvial sapphire. Tao Hsu and her coauthors survey mining and the importance of gem tourism to the areas, noting that larger, mechanized operations are expanding production at these sources.

LAB NOTES

fluorescent stone
No visible difference in color appearance or transparency was noted when the fluorescent stone was flanked by nonfluorescent diamonds of similar color in a color grading environment.

Specimens seen at GIA’s labs include a diamond with concentric inclusions, natural conch “rosebud” pearls, and CVD synthetic diamond overgrowth on a natural diamond.

MICRO-WORLD

ruby
The red color of the oil within the cavity of a ruby displays a remarkable contrast with the bodycolor of the gem. Unlike the flattened bubbles regularly encountered, a rounded bubble attests to the size of the cavity containing the oil. Photo micrograph by E. Billie Hughes; field of view approximately 2.5 mm.

G&G’s newest section describes a mysterious iridescence present in a rough aquamarine, a Christmas tree-shaped laser manufacturing remnant in a diamond, and a ruby treated with red oil.

GEM NEWS INTERNATIONAL

opal
Gem-quality common opal was recently discovered in Michoacán State in western central
Mexico. The approximate size of this sample is 15.04 × 7.68 × 5.57 cm. Photo by M.
Ostrooumov.

The Summer GNI section features reports on a newly discovered sapphire deposit in Ethiopia, dyed yellow bead-cultured pearls imitating South Sea cultured pearls, and a tri-color-change holmium-doped synthetic cubic zirconia.

2017 G&G CHALLENGE

The 2017 G&G Challenge is still open! Score 75% or better and you’ll receive a certificate of completion (PDF file). Earn a perfect score and your name will be listed in the Fall 2017 issue. Mail-in cards and online entries for the Challenge must be submitted by Friday, August 11, 2017.

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