corundum, geology.11, sources.12, Rwanda.12, gems

Yet another new locality for natural blue and treatable sapphire surfaces in this description of material from the Cyangugu district of South West Rwanda. Following summary descriptions of the sapphires' geologic setting and apparent origin from alkali basalts, the results of testing 20 samples is reported. Absorption spectra (visible and infrared), quantitative chemistry (microprobe), and microthermometry were performed on two specially prepared samples. Ten prepared specimens were examined by SEMEDS for inclusions, and eight rough samples were also studied by SEM for detailed surface analysis. The appar ently meticulous methodology yielded high-quality detailed information that is a welcome addition to the gemological literature, despite the small sample size. Numerous illustrations also indicate that this material yields fine-quality gems of brilliant blue color. However, no mention is made of its commercial availability or potential supply.

corundum, inclusions.5, Burma.12, gems

Mong Hsu rubies are characterized by a black sapphire core and a ruby rim. This color zoning has been correlated with the presence of the trace elements Ti (violet to black) and Cr (red). Some examples of Mong Hsu rubies show a complex chemical zonation, which results in multiple zones of rubies, violet sapphires and black sapphires within one particular crystal. Rubies of this type have been studied by analyzing the solid and fluid inclusions as well as their chemical zoning. Minerals accompanying the rubies, such as tourmaline (dravite) and tremolite have also been analyzed. The formation conditions of the rubies have been reconstructed following the study of mineral associations and fluid inclusion analyses. Mong Hsu rubies were formed at 2–2.5 kbar and at temperatures between 500° and 550°C. The fluids were found to be water-bearing and multi-volatile CO₂-rich (multivolatile = composed of CO₂, CH₄ and other components, possibly N₂, H₂S and HF). Fluorite inclusions in the rubies indicate that fluids must have contained some HF. During the study of the homogenization temperatures in different populations of fluid inclusions, it was concluded that no major variations in temperature and pressure occurred during the growth of Mong Hsu rubies. However, the chemical zonation patterns found in Mong Hsu rubies and accompanying tourmalines are indicative of variations in the composition of the fluids, e.g. in contents of F, Ti and Cr. A preliminary model is proposed, which explains the cyclic growth of Mong Hsu rubies, with formation of alternating zones of ruby and sapphire by variation in HF concentration in the surrounding fluids. The possible multiple infiltration of fluids from metapelites into dolomites is discussed.

corundum, ruby, synthetic corundum.7, Vietnam.12, gems

corundum, inclusions.5, gems

corundum, Burma.12, color.4, inclusions.5, gems, infrared, IR, spectroscopy, ruby, Mong Hsu, heat treatment

The infrared absorption of the rubies from Mong Hsu was analyzed in order to classify the absorption features recorded. In the mid-infrared region, it was possible to distinguish two separate types of spectra. The first type was recorded in non-heat-treated ruby samples in the region from 1900 to 3400 cm⁻¹, identifying inclusions of diaspore. The second type was recorded in heat-treated ruby samples in the region from 3100 to 3600 cm⁻¹, indicating structurally bonded OH groups. Detailed for the first time in corundum, the building of OH groups is accomplished as a direct result of the dehydration of diaspore inclusions, demonstrated through heat treatment experiments.

corundum, inclusions.5, treatments.6, synthetic corundum.7, gems

An extensively illustrated reference on gemstone identification through the examination of inclusions, written in Chinese with supplementary English captions. Lai begins with practical guidance on observing and locating diagnostically significant internal features, then surveys the major gem species, covering natural and synthetic materials as well as treated and enhanced specimens. Numerous color photomicrographs provide a visual basis for comparison, with several images on each opening illustrating the diversity of internal characteristics encountered in gemological examination. The English captions make much of the photographic material accessible to readers unfamiliar with Chinese. The volume’s principal strength is its extensive photographic documentation: a contemporary reviewer judged the images comparable with, and in some instances superior to, those in other established inclusion references.

corundum, synthetic corundum.7, gems

Greek manufacturer A. Douros introduced a new flux synthetic ruby in early 1993. Grown by spontaneous nucleation in a lead-based solvent, the Douros synthetic ruby occurs as rhombohedral single crystals and twinned tabular crystals, as well as in clusters. The tabular crystals typically have intense red cores that gradually decrease in saturation to a near-colorless outermost layer; the rhombohedral crystals have a deep red body and a thin near-colorless layer on the rhombohedral faces, with umbrella-like growth patterns in some areas. Some samples contain distinctive inclusions of yellow residual flux with spherical bubbles. Chemically, the crystals are heavily zoned, and EDXRF analyses revealed variable trace amounts of Ti, Fe, Cr, and Ga, as well as some Pb; SEM-EDS identified the flux particles as lead-bearing. Microprobe analyses showed high Cr values in the crystal cores; in certain growth zones, Fe replaces Cr in the outermost layers. If inclusions or typical growth structures are not present, chemical composition appears to be the best means of separating these Douros synthetic rubies from natural rubies.

gems, inclusions, beryl, emerald, Madagascar

Inclusions in emeralds from the Mananjary region in the eastern part of the island nation of Madagascar are reported and compared with inclusions in emeraldsf rom other, especially African, localities. Although most of these internal features are similar to those found in emeralds from other schist-type deposits, Mananjary emeralds usually can be separated from emeralds from other localities by means of associations of certain mineral inclusions (especially talc, carbonates, amphiboles, and quartz) with specific types of fluid inclusions.

gems, spinel, synthetic spinel, flux synthetic spinel, Russia

Examination of red and blue samples of relatively new flux synthetic spinel from Russia established criteria by which they can be separated from their natural counterparts. The flux synthetic blue spinels can be recognized on the basis of their inclusions, ultraviolet luminescence, and visible absorption spectrum. Magnification is insufficient to identify the flux synthetic red spinels when flux or metallic inclusions are present; in the absence of such inclusions, however, chemical analysis is required. Red and blue natural spinels both contain significantly more zinc than their flux synthetic counterparts. Also, trace amounts of Pb (from the flux) and Pt and Ir (from the crucible) were found in some of the flux synthetic spinels.

jade, jadeite, fei cui, nephrite, archaic jade, China, gems

The Worrell Collection of Chinese jade animals has been assembled by T. Eugene Worrell, who is an avid outdoorsman and a noted animal art collector who resides in Charlottesville, Virginia. Believed to be unique among American jade collections, it numbers more than 150 carvings of real and imagined creaturess from the legendary Chinese bestiary, dating from the neolithic age to the twentieth century. Forty-one examples from the collection were chosen by John Ayers for inclusion in this book. Under his scholarly pen, A Jade Menagerie becomes an indispensable reference for the serious collector and a delightful introduction to jade collecting for everyone.