corundum, Malawi.12, gems

An unusual form of “silk” is described in sapphires offered on the London market and reported to originate from Chimwadzulu near Blantyre, Malawi, rather than the Umba River district of northern Tanzania, with whose material they had initially been associated. Parcels encountered over approximately a decade consisted chiefly of rather washed-out blue stones, often lacking brilliance, together with some finer examples, fancy colors, and color-change specimens. Their inclusions and fractures generally resembled those in Tanzanian sapphires. Heating to improve color was suspected as a possible cause of some fractures, but was not established. A small number of stones contained conspicuous, coarse silk differing markedly from the familiar rutile needles of corundum. Under magnification, the features appeared as extremely thin, apparently hollow cavities arranged in straight lines, frequently intersecting at nearly right angles. Some were sufficiently thin to produce Newtonian interference colors in reflected light. Angular relationships were investigated by photographing one specimen through its table facet, preparing a negative print, extending the inclusion traces, and measuring their intersections with an ordinary protractor. The predominant intersections were approximately 87° and 93°, broadly approaching the angle between corundum rhombohedral faces; another group approached the angle between a rhombohedral face and the basal pinacoid. Nevertheless, recorded angles ranged widely, from about 4° to 161°, and individual cavities included narrow wedges as well as broader angular forms. The author acknowledges substantial measurement limitations arising from the width of the traces, approximate determination of their centers, and the inclination of some inclusions away from the principal observed plane. These uncertainties do not, in his assessment, explain the departure from the usual 120° relationships associated with corundum silk. Comparable features were observed in approximately six stones, most showing mainly the nearly perpendicular intersections. A possible relationship to normal sapphire parting directions is suggested, but neither the linear arrangement nor the varied cavity shapes is explained. The observations document an unusual inclusion pattern, interpreted as exsolution cavities, while leaving its formation and crystallographic controls unresolved.

corundum, synthetic corundum.7, flux, Knischka, gems

Gunawardene examines the gemmological and crystallographic characteristics of the newly developed Knischka synthetic ruby, produced by Paul Otto Knischka of Austria using a modified gradient-transport technique involving supercooling and supersaturation. The paper describes the unusual crystal morphology of the material, including the development of numerous additional crystal faces, and compares these forms with those of natural corundum. Particular attention is given to microscopic identification. Characteristic internal features include turbid clouds, swirls of colour, liquid or feather-like patterns, negative crystals associated with elongated crystalline tubes, metallic platelets, melt residues and two-phase inclusions. Although some inclusions can resemble features in natural ruby or other synthetic rubies, their morphology and associations provide useful criteria for recognizing Knischka material. The study emphasizes microscopy as the principal means of identification and illustrates the diagnostic inclusions and crystal-growth features in detail.

corundum, treatments.6, heat, gems

We have been told that conservative gem traders in Sri Lanka have been reluctant to start heat treating their own geuda" corundum, fearful of the impact this would have on the market for blue and yellow sapphires mined on the island. However, the heat treatment activities of Thai op-erators using the "geuda" have al-ready placed the Sri Lankans in com-petition with themselves for these colored sapphires. A new gas oven from Japan that can be used with ei-ther a reducing flame (for blue sap-phires) or an oxidizing flame (for ru-bies and yellow/orange sapphires) could encourage heat treatment of corundum in Sri Lanlza."

gems, jade, jadeite, fei cui, Mesoamerica, Mexico, Guatemala, Costa Rica, Mayans, Olmecs, Aztecs, archaeology, history, archaeogemology, Pre-Columbian jade; Costa Rica; Maya; exchange; iconography, lapidary

For scholars involved in the reconstruction and interpretation of Mesoamerican social and cultural systems, Pre-Hispanic clothing provides a rich repository of valuable and revealing ethnographic data. This is particularly true in the case of special-purpose ritual garments. These esoteric costumes often contain clues as to their own probable place of origin and the rationale underlying their adoption by other peoples. The discovery of such information leads to a much fuller understanding and appreciation of the pageant-like ceremonies in which these symbolic costumes played such an intricate role. The subject of this paper, the Aztec quechquemitl, is an excellent and intriguing example of just such an enigmatic yet informative garment. The Nahuatl term quechquemitl probably comes from the word quechtli, “neck,” and quemi, “to put on a manta or cape” (Molina 1970: 88v). This female costume, often referred to in the literature as a shoulder shawl or neck cape, is still being worn today. It is made by joining two rectangles of material in such a way that when they are laid one atop the other a square is formed with a V at the neck (Fig. 1). When the costume is put on and its points turned front and back, the sloped shoulders of the wearer give the garment a unique triangular appearance. However, when the points of the quechquemitl are worn to the side, it is no longer so easily identified (Fig. 2); a scholar tracking the quechquemitl must be sharp-eyed indeed. In addition to being a rich repository of food, these fabled “Hot Lands” were famous for their highly desirable luxury goods. Tribute from this region consisted of such raw materials as feathers, down, and jadeite, and of worked items such as turquoise mosaics, warrior costumes, and strings of jade and turquoise stones (Berdan n.d.: 350). Most highly valued of these imported commodities, however, was cotton, the status fabric par excellence of the Aztec world.

gems, emerald, beryl, Brazil, Bahia, Carnaíba, Salininha, Fazenda do Pombo, Açude Sossego, Brumado, Ceará, Tauá, Minas Gerais, Itabira, Santana Dos Ferros, Goiás, Fazenda das Lages, Santa Terezinha

The aim of the present work is to put together important information on emeralds unearthed over the 8,500,000 square kilometers of Brazil. Aspects of history, general geology, mining, production and reserves have been described from the ten most important mines or occurrences. Gemological data such as optical and physical properties, quality grades, fashioning and commercial aspects have been emphasized from the ten deposits described herein, whenever data or samples were available. Careful attention was dedicated to the Carnaíba Mine, which is the largest and most traditional, the Itabira Mine, where a mechanized extracting program is being developed, and Santa Terezinha de Goiás, being the newest and with high concentrations in its deposits. The existence of the three mentioned deposits with their high potentialities places Brazil amongst the most important emerald producers in the world.

gems, lapis lazuli, Afghanistan, history of gemology, gem trade, Central Asia, locality, species, trade routes

Archaeological and textual evidence of the fourth and third millennia are used to reconstruct a trade route for lapis-lazuli. Originating in Badakhshan. this route probably traversed Kerman (Aratta). Fars (Anshan) and Khuzistan (Susa). The present reconstruction argues against control of the lapis trade by such northern communities as Hissar and Gawra. and minimizes the role of the Great Khorasan (Silk) Route.

gems, corundum, synthetic corundum.7, flux ruby, Knischka ruby

Discusses the growth and features of Paul Knischka’s flux-grown synthetic ruby. Corundum was crystallized synthetically by an as yet undisclosed method of gradient-technique, through super-cooling and super-saturation. The finished crystals have flat, brilliant growth-faces and mineralogically significant indices, whose great number as well as combination has heretofore been unobserved. The elementary nuclei can be grown to macroscopic single crystals, twins or multiple-complexes, phantoms, as well as clusters. The trade mark (K was formed using the initials of Paul Knischka's name with the P" inverted. These synthetic rubies are, once cut, distinguishable from natural ruby in the same manner as natural ruby is distinguished from synthetics of other makes and methods."

tourmaline, cat’s eye, gems

The causes of chatoyancy in tourmaline are investigated through examination of twenty-two specimens representing different colours, localities and types of elongated inclusion. Polished slabs and cat’s-eye cabochons from Brazil, the United States and Mozambique were studied by optical microscopy, X-ray powder diffraction, electron-microprobe analysis and heating-stage observation of fluid inclusions. The host crystals were assigned principally to elbaite, with fewer dravitic specimens, using unit-cell parameters because conventional refractive-index and density measurements proved insufficiently reliable in the inclusion-rich material. No close relationship was established between tourmaline colour and this structural classification. Three main inclusion types are distinguished: irregular thread-like trichites, growth tubes and solid needles. Trichites commonly contain two-phase fluids and occupy healed fractures, but their variable orientation prevents them from generating a coherent cat’s-eye effect. Chatoyancy instead arises from densely distributed tubes or needles aligned parallel to the host’s principal growth direction. Growth tubes are interpreted as primary cavities associated with growth irregularities, strain or rapid crystallisation, whereas needles are elongated crystalline inclusions incorporated during growth. Within the examined suite, tubes occur more frequently in green tourmalines, while needles predominate in pink-red and blue specimens; trichites show no comparable colour association. Microchemical analyses indicate that the most common solid material filling the tubes is tourmaline with a composition and minor-element pattern similar to those of its host. Less common fillings include prosopite and cookeite, together with iron oxides and sulphides. Opaque channel material is identified as pyrrhotite, while red-to-brown coatings and iron-rich yellow halos are attributed more tentatively to iron oxides or hydroxides. Most fine crystalline needles likewise have compositions matching tourmaline. Other straight rods are identified as epidote close to clinozoisite in composition. Columnar aggregates of subhexagonal muscovite plates are also described. Heating-stage behaviour of two-phase inclusions suggests water and carbon dioxide as principal constituents, supporting a hydrothermal setting, while several associated minerals are consistent with late pegmatitic or hydrothermal processes. The study concludes that tourmaline chatoyancy cannot be assigned to a single foreign mineral inclusion: both aligned growth channels with varied fillings and crystalline needles, commonly themselves tourmaline, can produce the effect.

gems, spinel, cobalt-blue spinel

gems, spinel, spinel inclusions, root-like inclusions

G.R. Crowningshield records unusual inclusion features observed during examination of natural pink and red spinels at the Gemological Institute of America’s New York laboratory. The note places these observations in the context of increasing consumer familiarity with pink and red spinel and their more frequent appearance in the gem trade, both locally and in East Asia. Several lots, together weighing hundreds of carats, provided the material examined. Among these collections, two stones attracted particular attention because their inclusions differed from the forms more commonly encountered in natural spinel. One contained branching, root-like inclusions whose appearance recalled features previously observed in diamond, another mineral of the cubic crystal system. Earlier published diamond observations are cited as visual comparisons, without establishing that the inclusions in the two host minerals have the same composition or origin. A second spinel contained a series of rounded, frosted-looking features likened to tennis balls. These are identified as negative crystals, despite their superficial resemblance to gas bubbles in slag glass. The comparison concerns their microscopic appearance rather than an identification of the spinel as glass or of the cavities as ordinary gas bubbles. A third illustration provides a contrast by showing more familiar inclusions, including octahedral forms, in a red spinel. Three photomicrographs accompany the account: root-like inclusions photographed with dark-field illumination at 20× magnification, rounded negative crystals at 30×, and common natural-spinel inclusions, also at 30×. Together, the images document both unusual branching structures and rounded cavities alongside the more recognisable octahedral forms. The report is descriptive and does not assign a mineral species to the root-like inclusions, specify the contents of the negative crystals, or propose a formation mechanism for either unusual feature. Its principal contribution is to broaden the documented range of inclusion appearances in natural spinel and to distinguish the observed negative crystals from the bubble-like features they visually resemble.