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

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.

corundum, inclusions.5, gems

gems, beryl, emerald, Egypt, inclusions

Egypt is the most ancient of sources for emerald. More than 2,000 years ago, emerald deposits in upper Egypt were supplying gems throughout the Graeco-Roman Empire. A recent visit to this emerald province revealed that the emeralds occur within a northwest-southeast trending belt of schistose rocks in the Red Sea Hills, near the port town of Marso Alam. At the time of the visit, there was no official commercial mining of emerald in the region, although there was evidence of sporadic activity by Bedouin tribespeople. Gemological examination of 14 cut emeralds and green beryls revealed properties consistent with those of material from similar geologic environments.

corundum, ruby, sapphire, treatments.6, inclusions.5, Colombia.12, Brazil.12, USA.12, Montana.12, Idaho.12, gems

gems, beryl, emerald, Colombia

A condensed historical and mining survey is followed by a compilation of the most notable crystals of Colombian emeralds ever found and of the details of their chemical composition. A summary of the elemental substitutions and their effects on the outlined range of gemmological data is given. Special emphasis is placed on the cause of the famous, vividly green coloration, i.e. on the selective absorption of orange-red and violet light, dictated by minor contents of the chromophoric elements Cr and V substituting for Al³⁺ in octahedrally coordinated sites of the beryl lattice (Cr ≈ V, with the Cr/V ratio found to be ranging from 4.5 to 0.5, in extreme cases from about 10 to 0.1). Iron, however, has barely been detected in the UV/VIS absorption spectra of Colombian emeralds. Though generally present in slightly larger amounts than Cr³⁺, iron does not recognizably influence the colour (little Fe²⁺ and possibly some Fe³⁺ positioned in the axial channels of the ring-silicate structure). A detailed presentation of the currently known internal characteristics (inclusions and growth structures) is supplemented by a discussion of identification problems with treated emeralds and the disclosure of the treatment during transactions in the wholesale and retail trade. Allocation of the emeralds to individual Colombian mines on the basis of inclusion patterns does not appear possible in most instances. However, the differentiation of Colombian emeralds from other natural emeralds (such as those from the Panjsher Valley exhibiting very similar (s,l,g) three-phase inclusions) or from difficult, modern hydrothermal and flux synthetics is shown to be feasible by a combination of microscopy, refractometry, and absorption spectrometry (UV/VIS and NIR/MIR), assisted by chemical analysis only in the most difficult cases. Safe identification of authenticity, treatment, and origin of emeralds, however, is increasingly becoming the task of the experts in the specialized laboratory. The mineralogical definition of emerald as a yellowish to bluish-green variety of natural beryl is shown to be valid for any Cr and V-containing variety except possibly the rare, absolutely chromium-free (V,Fe)-beryls (modification of the former definition of type II emerald): in many of the preferred Colombian emeralds, chromium is clearly dominated by vanadium (Cr/V ratio < 1). However, chromium has a higher efficiency of coloration than vanadium and a much higher one than iron ions in the various substitutional and interstitial lattice sites of beryl. Cr influences colour even at very low trace levels. An extensive and up-dated selection of literature, covering all aspects cited, completes the synopsis.

gems, beryl, emerald, Colombia

A condensed historical and mining survey is followed by a compilation of the most notable crystals of Colombian emeralds ever found and of the details of their chemical composition. A summary of the elemental substitutions and their effects on the outlined range of gemmological data is given. Special emphasis is placed on the cause of the famous, vividly green coloration, i.e. on the selective absorption of orange-red and violet light, dictated by minor contents of the chromophoric elements Cr and V substituting for Al³⁺ in octahedrally coordinated sites of the beryl lattice (Cr ≈ V, with the Cr/V ratio found to be ranging from 4.5 to 0.5, in extreme cases from about 10 to 0.1). Iron, however, has barely been detected in the UV/VIS absorption spectra of Colombian emeralds. Though generally present in slightly larger amounts than Cr³⁺, iron does not recognizably influence the colour (little Fe²⁺ and possibly some Fe³⁺ positioned in the axial channels of the ring-silicate structure). A detailed presentation of the currently known internal characteristics (inclusions and growth structures) is supplemented by a discussion of identification problems with treated emeralds and the disclosure of the treatment during transactions in the wholesale and retail trade. Allocation of the emeralds to individual Colombian mines on the basis of inclusion patterns does not appear possible in most instances. However, the differentiation of Colombian emeralds from other natural emeralds (such as those from the Panjsher Valley exhibiting very similar (s,l,g) three-phase inclusions) or from difficult, modern hydrothermal and flux synthetics is shown to be feasible by a combination of microscopy, refractometry, and absorption spectrometry (UV/VIS and NIR/MIR), assisted by chemical analysis only in the most difficult cases. Safe identification of authenticity, treatment, and origin of emeralds, however, is increasingly becoming the task of the experts in the specialized laboratory. The mineralogical definition of emerald as a yellowish to bluish-green variety of natural beryl is shown to be valid for any Cr and V-containing variety except possibly the rare, absolutely chromium-free (V,Fe)-beryls (modification of the former definition of type II emerald): in many of the preferred Colombian emeralds, chromium is clearly dominated by vanadium (Cr/V ratio < 1). However, chromium has a higher efficiency of coloration than vanadium and a much higher one than iron ions in the various substitutional and interstitial lattice sites of beryl. Cr influences colour even at very low trace levels. An extensive and up-dated selection of literature, covering all aspects cited, completes the synopsis.

beryl, chrysoberyl, beryl, emerald, alexandrite, Russia, Urals, Malysheva, gems

Emeralds are again being mined in the historic district of the Ural Mountains. Physical, chemical, spectroscopic, and ini-croscopic characteristics of stones from the recent production are presented and com-pared with data on older samples as well as those reported in the literature. Chemi-cal analysis and visible and infrared spec-troscopy provide information on crystal chemistry and color-causing trace ele-ments that is useful both to characterize these stones and to separate them from their synthetic counterparts. A variety of mineral inclusions as well as liquid, two-phase, and three-phase inclusions were seen with magnification. All of the data are critically evaluated with respect to the confirmation of unknown samples as Uralian.

corundum, ruby, Kenya.12, East Africa, inclusions.5, gems