Gems & Gemology

The first decade of the 2000s continued the trend of using more powerful analytical instruments to solve gem identification problems. Advances in gem treatment and synthesis technology, and the discovery of new gem sources, led to urgent needs in gem identification. These, in turn, led to the adaptation of newer scientific instruments to gemology. The past decade witnessed the widespread use of chemical microanalysis techniques such as LA-ICP-MS and LIBS, luminescence spectroscopy (particularly photoluminescence), real-time fluorescence and X-ray imaging, and portable spectrometers, as well as the introduction of nanoscale analysis. Innovations in laser mapping and computer modeling of diamond rough and faceted stone appearance changed the way gemstones are cut and the manner in which they are graded by gem laboratories.

Kyanite derives its name from the Greek word for blue, due to its typical color. Gem-quality green kyanite has also been seen (e.g., Winter 2001 GNI, pp. 337-338), and colorless or yellow varieties have occasionally been faceted. Recently, however, orange kyanite has appeared in the gem market. The material was mined at Loliondo, Tanzania, near the area that recently produced fine crystals of spessartine (see, e.g., Spring 2008 GNI, pp. 76-78).

Since late 2007, rubies and sapphires have been mined by hand methods from both eluvial and primary deposits at Winza in central Tanzania. The gem corundum is related to "dikes" of amphibolitic rocks that belong to the Paleoproterozoic Usagaran Belt. Based on crystal morphology, Winza corundum is subdivided into two types: prismatic-tabular-rhombohedral and dipyramidal. In general, medium red and dark (orangy) red top-quality rubies are rhombohedral. Pinkish red and purplish red rubies, as well as pink, purple, and blue (often strongly color zoned) sapphires are, for the most part, dipyramidal. The top-quality rubies are characterized by a distinct assemblage of long tube-, fiber-, needle-, or hair-like inclusions containing an orange-brown material (most likely limonite). The lower-quality material generally contains a larger amount of solid inclusions (mostly amphibole crystals), fissures, and growth features. Unique to corundum from this locality are bluish violet color zones oriented parallel to the prism and basal pinacoid, and occasionally also parallel to rhombohedral and dipyramidal faces. The relatively high Fe content of Winza rubies separates them from most other natural and almost all synthetic counterparts.

Data for global annual rough diamond production (both carat weight and value) from 1870 to 2005 were compiled and analyzed. Production statistics over this period are given for 27 diamond-producing countries, 24 major diamond mines, and eight advanced projects. Historically, global production has seen numerous rises - as new mines were opened - and falls - as wars, political upheavals, and financial crises interfered with mining or drove down demand. Production from Africa (first South Africa, later joined by South-West Africa [Namibia], then West Africa and the Congo) was dominant until the middle of the 20th century. Not until the 1960s did production from non-African sources (first the Soviet Union, then Australia, and now Canada) become important Distinctions between carat weight and value affect relative importance to a significant degree. The total global production from antiquity to 2005 is estimated to be 4.5 billion carats valued at US$300 billion, with an average value per carat of $67. For the 1870-2005 period, South Africa ranks first in value and fourth in carat weight mainly due to its long history of production. Botswana ranks second in value and fifth in carat weight although its history dates only from 1970. Global production for 2001-2005 is approximately 840 million carats with a total value of $55 billion, for an average value per carat of $65. For this period, USSR/Russia ranks first in weight and second in value, but Botswana is first in value and third in weight just behind Australia.

Chemical and microscopic examination of the first gem-quality synthetic emeralds of facetable size proves that Prof. Richard Nacken grew two main types of emerald by flux methods in the mid-1920s. One of these two types, grown with colorless beryl seeds in molybdenum-bearing and vanadium-free fluxes, has not previously been mentioned in the literature and would appear to be unknown to gemologists. The other main type, which has already been described in gemological publications, was grown from molybdenum-and vanadium-bearing fluxes. In drawing these conclusions, rough and faceted synthetic emeralds produced by Nacken were available for study from two principal sources: the Deutsches Museum in Munich, to which Nacken had donated samples in 1961, and family members who had inherited such crystals. Chemical, morphological, and microscopic properties are given, and circumstances concerning the developmental history of the Nacken production, including the possibility of collaboration with IG Farben (a subject of past speculation), are discussed as well. The latter has recently been elucidated by the discovery of original documents from the IG Farben gemstone plant, preserved in the Archives of the German Federal State of Saxony-Anhalt.