Fall 2019 G&G: Gem Art of the Taj Mahal, Fancy White and Black Diamonds, and Unique Inclusions in Thai Corundum
November 19, 2019
The Fall 2019 edition of Gems & Gemology opens with a look at the rich gem history of the Mughal dynasty and the intricate gem inlay work of the Taj Mahal. The issue also features an investigation into the cause of color in Fancy white and Fancy black diamonds, mineral inclusions in corundum from the Bo Welu deposit in Thailand, characteristics of hydrothermally treated amber, and more.
Gemstones in the Era of the Taj Mahal and the Mughals
The lead article, by Dona Mary Dirlam and co-authors, looks back to the seventeenth century and the Mughal dynasty that ruled much of India. The Mughals collected extraordinary jewelry and gems and transported these riches across intricate trade routes. Emperor Shah Jahan commissioned the building of the iconic Taj Mahal, which features elaborate decorative parchin kari inlay of ornamental and fine gems.
Natural-Color Fancy White and Fancy Black Diamonds: Where Color and Clarity Converge
Sally Eaton-Magaña and Christopher M. Breeding continue their series of colored diamond characterization studies with a look at Fancy white and Fancy black diamonds. These two colors are distinctive for their cause of color: nanometer- to micrometer-sized inclusions that reduce the diamond’s transparency, rather than atomic-scale defects typical of other fancy-color diamonds.
Unique Vanadium-Rich Emerald from Malipo, China
Yang Hu and Ren Lu provide an overview of the history, resource potential, and geology for emeralds from Malipo County in southwestern China. Malipo emerald has unique multiphase inclusions and a distinct chemical composition that helps separate it from other deposits.
Mineral Inclusions in Ruby and Sapphire from the Bo Welu Gem Deposit in Chanthaburi, Thailand
Supparat Promwongnan and Chakkaphan Sutthirat discuss the various mineral inclusions observed in Bo Welu ruby and sapphire. Some newly reported mineral inclusions in Thai corundum—sillimanite, nepheline, quartz, alkali feldspar, spinel, and anhydrite for ruby and purple sapphire, and sulfide for blue sapphire—can be used to support origin determination.
Characteristics of Hydrothermally Treated Beeswax Amber
Hydrothermal treatment optimizes the appearance of semi-translucent to opaque “beeswax” amber and expands the availability of amber products. Yamei Wang and co-authors explore the characteristics of hydrothermally treated beeswax amber to assist with identification challenges.
Effects of Mollusk Size on Growth and Color of Cultured Half-Pearls from Phuket, Thailand
In order to find ways to increase the overall production and value of cultured half-pearls, Kannika Kanjanachatree and a team of researchers studied 400 Pteria penguin mollusks over a period of 10 months. They set out to determine the optimum mollusk size, compare rejection and mortality rates, and chart the color and quality of cultured half-pearl samples from month to month. Their findings have important consequences for color-matching of half-pearls.
Hydrogen-Rich Green Diamond Color-Treated by Multi-Step Processing
Identifying the color origin of green diamonds is sometimes difficult for gemological laboratories. In this article, Wenqing Huang and co-authors propose two alternative multi-step treatment procedures that would explain the combination of spectroscopic features observed in a 0.25 ct color-treated yellowish green diamond.
Pressed Gibbsite and Calcite as a Rhodochrosite Imitation
Hanyue Xu and Xiaoyan Yu investigate the differences between rhodochrosite and a new rhodochrosite imitation that has recently appeared in the market. Standard gemological testing can identify the imitations, which are composed of pressed gibbsite and calcite powder with a granular structure.
GIA laboratory staff members present their latest findings in the Lab Notes section, including a star-shaped cloud inclusion in a faceted diamond, new resin imitations of ivory, and a cobalt-coated sapphire.
The Micro-World section, dedicated to the inner world of gemstones, features a rain cloud in alexandrite, an intergrowth of iolite and sunstone, and an abundance of pyrite inclusions in dravite from Mozambique.
Gem News International
Finally, GNI correspondents from around the world report on a new source of Nigerian aquamarine, black non-nacreous pearl imitations made of beads cut from shell, and the new mineral johnkoivulaite, named after renowned gemologist and photomicrographer John Koivula.
Brooke Goedert is associate editor of Gems & Gemology at GIA in Carlsbad, California.