taaffeite, Sri Lanka, gems

Gübelin describes “taprobanite,” a rare red gemstone from Sri Lanka initially thought to be taaffeite because of its similar appearance and gemological properties. Detailed examination showed it to represent a distinct member of the taaffeite mineral group, characterized by differences in chemical composition, crystallographic properties, and optical behavior. The study discusses its identification, physical and optical constants, absorption characteristics, inclusions, and relationship to taaffeite, emphasizing the difficulty of recognizing such rare stones by conventional gemological testing alone. The name derives from Taprobane, the ancient name for Sri Lanka.

corundum, inclusions.5, diamond, beryl, emerald, spectroscopy, gems

Dele-Dubois, Dhamelincourt, and Schubnel examine the application of Raman spectroscopy to the non-destructive identification of mineral inclusions in diamonds, sapphires, and emeralds. The technique permits inclusions to be analyzed in situ through the host gemstone by means of their characteristic Raman spectra, avoiding the need to extract or otherwise damage them. The authors demonstrate the usefulness of Raman spectroscopy for identifying very small inclusions that may be difficult to determine by conventional microscopy, illustrating its value both for gemological identification and for investigating the mineral assemblages trapped during gemstone formation.

diamond, inclusions, gems

Gübelin reviews the nature and significance of mineral inclusions in natural diamond, considering included minerals as evidence bearing on diamond formation and its geological environment. The paper surveys the principal types of mineral inclusions recognized in diamonds and discusses their mineralogical relationships and importance for understanding the conditions and processes of diamond genesis.

beryl, emerald, Colombia, gems

Barriga Villalba and Barriga del Diestro present a monographic study of Colombian emerald, describing its principal characteristics and properties. The work considers emerald as a mineral and gemstone, with attention to its physical and optical properties, characteristic color and inclusions, and the features associated with Colombian material. It also discusses the geological occurrence and principal emerald-producing areas of Colombia, particularly the deposits of the Eastern Cordillera, and addresses aspects of mining and the evaluation of emeralds. The volume provides a contemporary Colombian account of the country’s most important gemstone and its distinguishing gemological and geological characteristics.

inclusions, gems

Gübelin examines the nature and significance of mineral inclusions in gemstones, treating inclusions as evidence of the geological conditions and processes under which their host crystals formed. He discusses the morphology, identification, orientation, and genetic relationships of included minerals and shows how inclusion assemblages and their relationships to other internal features can assist in gemstone identification and provide information on genesis and, in favorable cases, origin. Particular emphasis is placed on systematic microscopic observation and on interpreting inclusions as records of a gemstone’s crystallization and subsequent geological history.

corundum, Canada.12, gems

Peterson discusses black star corundum, a dark variety of corundum that displays asterism when cut en cabochon. The article describes the appearance and gemological characteristics of the material and the inclusions responsible for the star effect, produced by oriented needle-like inclusions that reflect light along crystallographically controlled directions. It considers the relationship between the dark body color, inclusions, and visibility of the star, as well as the orientation required in cutting to display the phenomenon effectively. The brief account provides a practical description of black star corundum and the optical phenomenon responsible for its distinctive appearance.

ekanite, gems

Gübelin gives a detailed gemological account of ekanite, a newly recognized metamict gem mineral from Ceylon, named for F. L. D. Ekanayake, who first recognized its unusual character. The material occurs in the gem gravels near Ellawala, northeast of Ratnapura, and is typically greenish-brown to yellowish-green, transparent to translucent, and sometimes displays chatoyancy or asterism caused by oriented clouds of minute inclusions. Gübelin describes its gemological properties, including its singly refractive character, refractive index of about 1.595, specific gravity of about 3.28, and weak absorption bands, together with microscopic features and inclusions. Chemical investigation showed calcium, thorium, silicon, aluminium, and lead, while measurements demonstrated significant radioactivity associated particularly with thorium. The destruction of the original crystal lattice through radioactive decay accounts for its metamict condition. Gübelin also discusses its probable original crystalline state, chemical composition, and age as estimated by thorium-lead dating, establishing ekanite as an unusual new addition to the gem minerals of Ceylon.

inclusions, garnet, gems

gems, gemology,

Chudoba and Gübelin provide a compact practical reference to gemology intended both for identifying gemstones and for standardizing the often confusing terminology used in the German gem trade. The principal gemstones and ornamental materials are arranged alphabetically and characterized by their chemical, crystallographic, and physical properties, important localities, trade names, and diagnostic features. Separate sections treat inclusions in natural gemstones, synthetic stones, doublets and triplets; tables of gemological constants; coated stones; synthetic gems and other imitations; the gemological microscope; and practical identification tables. Particular emphasis is placed on simple tests that can be performed with readily available gemological instruments and on microscopic inclusions as a means of distinguishing natural stones from synthetics and assembled or imitation materials. Conceived as a concise working handbook rather than a comprehensive mineralogical treatise, it became the basis for the substantially enlarged second edition of 1966, retitled Edelsteinkundliches Handbuch, and a further expanded third edition in 1974.

corundum, ruby, sapphire, Sri Lanka.12, gems

A concise account of the crystalline rocks of Ceylon, intended to summarize their character and classification as then understood. Coomaraswamy discusses the terminology of “gneiss” and “granulite,” preferring the latter for many Ceylonese rocks, and regards them as belonging to the Charnockite Series described from southern India, the two regions forming a closely related petrographical province. He describes the principal rock types and their mineral banding, together with the crystalline limestones and rocks intermediate between limestone and granulite. The latter may contain diopside, phlogopite, amphibole, scapolite, spinel, sphene, calcite and, more rarely, serendibite, and may occur at limestone–granulite contacts, as inclusions, dykes or bands; some also yield mica of commercial value. Coomaraswamy argues that, whatever their ultimate origin, the crystalline limestones were essentially contemporaneous with the granulites and crystallized under broadly comparable high-temperature conditions. He also distinguishes the wollastonite-bearing Galle group and discusses the structural geology of the crystalline series, particularly foliation, folding and the influence of rock structure on the development of parallel strike valleys such as those around Hatton. The paper is an important early synthesis of Ceylon’s Precambrian crystalline geology and provides geological context for the mineral and gem deposits associated with these rocks.