gems, garnet, Spain

Tertiary dacites and rhyodacites in southeastern Spain contain garnets both as phenocrysts within the volcanic lavas and within enclosed metamorphic xenoliths. Microprobe analyses reveal that garnets from both the calc-alkaline lavas and the metamorphic inclusions are compositionally similar, being rich in almandine. However, their zoning patterns differ: garnets in the lavas exhibit normal zoning or slight manganese enrichment at the rims, while those in xenoliths show Mn-enriched edges or reverse zoning. These differences in zoning and petrographic features suggest that the volcanic garnets crystallized early from the calc-alkaline magma, whereas the more uniform composition and low pyrope and grossular content in the dacitic and rhyodacitic garnets imply that the crystallization conditions were only briefly maintained.

corundum, inclusions.5, gems

The scanning electron microscope (SEM) provides a powerful new tool for the study of daughter minerals in fluid inclusions, particularly when the instrument is equipped with a solid-state X-ray detector. The general character and abundance of inclusions is first established by conventional optical study of polished plates of the host crystal. These plates or other pieces of the same material are cleaned and then opened by chipping or cleaving. Under the SEM, open inclusions appear as pits in the newly broken surfaces. Upon enlargement, daughter crystal morphology is revealed in great detail and the electron beam produces characteristic X-ray spectra of the daughter mineral which are collected by an energy dispersive detector and visually displayed on a multichannel analyzer. The resulting chemical and morphological information, coupled with previous optical observations, defines or greatly limits the possible identity of the daughter mineral. Three applications of the SEM technique are presented in this paper. The method is first applied to complex inclusions in fluorite of the Emmett mine, Jamestown, Colorado, in which nine previously unidentified daughter minerals were found. Dawsonite [NaAl(CO₃)(OH)₂] is confirmed as a daughter precipitate in inclusions in gold-quartz veins of the Oriental mine, Alleghany, California. Finally, the SEM is used to identify daughter minerals in both magmatic and hydrothermal inclusions from the carbonatite at Magnet Cove, Arkansas.

gems

gems, jade, jade imitations, glass

Imitation jades currently circulating in jewellers market under the name of Syberian jade or Reformed jade were investigated by both non-destructive and destructive methods, with special attention to the inclusions. The imitation jades are made of sophisticatedly produced glass, and are dark green, translucent to opaque with glassy, somewhat greasy, luster, have Mohs' hardness of 5-5.5, sp. gr. 2.67 ± 0.02 at 20℃, refractive index 1.523 ± 0.005, and broad absorption spectrum at 4000-4600Å and 6300-7000Å. They contain characteristic inclusions of the following three types; 1) Needle-like inclusions which are identified to be hydroxyl apatite by optical and X-ray investigations, have hexagonal section, and are uniaxial negative, with no pleochroism, higher refractive index than the matrix. These are grouped into three by their length. 2) Dendrite inclusions with 90° braches are identified to be either vapour or liquid phase inclusions, and have lower refractive index than the matrix. 3) Four other types of inclusions, which are not identified. These imitation jades exhibit psudo-optical anisotropy due to apatite inclusions and are easily identified by their inclusions.

quartz, inclusions, gems

Burma.12, corundum, ruby, inclusions.5, gems

inclusions, gems

Burma.12, corundum, ruby, inclusions.5, gems

Eppler examines inclusions observed microscopically in Burmese ruby and discusses their value for characterizing the material. Illustrated with nine figures, the paper describes characteristic internal features, including mineral inclusions and growth-related structures, and considers their appearance and identification under the microscope. Particular attention is given to features useful in recognizing natural Burmese ruby and understanding its formation, demonstrating the importance of inclusions both as diagnostic gemological evidence and as indicators of the geological environment in which the corundum crystallized.

gems, jade, jadeite, fei cui, Mesoamerica, Mexico, Guatemala, Costa Rica, Mayans, Olmecs, Aztecs, archaeology, history, archaeogemology

Up to the present, the only jadeite deposits known in Mesoamerica are located north of Manzanotal, a settlement situated east of San Cristóbal Acasaguastlán in the middle course of the Motagua River Valley (Foshag and Leslie 1955; Barbour 1957). New deposits were discovered by E. Böse during a period of geological studies carried out in the region and were visited by the authors in July 1965. Most of these albite and jadeite deposits are located north of the paved Guatemala–Puerto Barrios highway, between the El Cintillo and Uyús rivers (see Figure 1), occurring as tectonic inclusions of varying dimensions within outcrops of foliated serpentinite. Becquelin and Bosc describe newly identified albite and jadeite occurrences near San Cristóbal Acasaguastlán in Guatemala’s middle Motagua Valley, where the deposits occur as tectonic inclusions of varying dimensions within foliated serpentinite. The authors report shallow pits surrounded by angular fragments of albite and jadeite, small mounds, terraces, and nearby obsidian blade fragments, which together suggest rudimentary extraction, possibly in prehistoric times, although they stress that further investigation is required to establish the nature and age of the workings. Other jadeite occurrences in the region lack evidence of ancient exploitation. The archaeological evidence from nearby Guaytán, Manzanotal, and other middle Motagua sites includes jade fragments, partly worked beads and drills, and a jadeite block bearing percussion marks. The authors suggest that inhabitants of the valley collected albite and jadeite from terraces and gravels of the Motagua and perhaps directly from serpentinite sources, manufactured beads and other simple ornaments, and exported jade as blocks and, in some cases, finished objects. They conclude that exploitation and trade in jade probably flourished during the Classic period and that the San Cristóbal region may have supplied a substantial portion of the jade used elsewhere in Mesoamerica.

corundum, sapphire, ruby, history.1, quality.10, gems

Bank presents an illustrated survey of gemstones, introducing their chemical and physical properties and explaining how these characteristics relate to identification. Individual gem materials are arranged according to mineralogical classification, linking their descriptions to the broader study of minerals. The text discusses inclusions and other diagnostic features, while locality maps provide geographical context for the occurrences described. Colour photographs form a major part of the presentation, allowing readers to appreciate the appearance and variety of gem materials alongside the scientific account. The work combines introductory explanations with information intended for readers already familiar with gemmology, serving as a general reference and visual survey. Its treatment of testing is selective, with less emphasis on absorption spectroscopy, and the individual descriptions do not consistently supply refractive-index and specific-gravity values. E.H. Rutland’s English translation makes Bank’s German account accessible to an English-speaking readership.