corundum, synthetic corundum.7, gems

A technique has been developed for calculating temperature fields (T-fields) in optical crystals in which heat exchange proceeds by both radiation and conductivity. The results of calculation of T-fields in corundum crystals grown by horizontal uniaxial crystallization are reported. The fields of the first and second temperature derivatives (T' and T'', respectively) have been considered in order to reveal crystal regions in which stress and dislocations are most probable to appear. A minimum, associated with the radiative-conductive heat exchange, has been found on the T'' curve in the vicinity of free crystal boundary. It is proved that a linear T-field cannot be obtained in optical crystals.

corundum, sapphire, color.4, spectra, gems

Schmetzer and Bank review the causes of color in corundum and its gem varieties ruby, sapphire, and padparadscha. They attribute coloration principally to transition-metal ions—iron, titanium, chromium, and vanadium—as well as to lattice defects. Natural corundum is rarely colored by only a single ion or ion pair; instead, many stones owe their appearance to several color-producing mechanisms acting simultaneously. Consequently, the absorption spectra of mixed-color corundums can be interpreted as superpositions of several fundamental spectral types, producing the wide range of colors observed in natural corundum.

corundum, ruby, sapphire, quality.10, gems

corundum, treatments.6, Sri Lanka.12, gems

corundum, Sri Lanka.12, gems

corundum, quality.10, gems

One of the world's largest and most memorable treasure chambers, the Diamond Treasury of the USSR, the Almazny Fond, is a veritably unique collection of gemstones, nuggets of precious metals and exquisite jewellery. The core and historical nucleus of this collection is comprised of what are commonly known as the Crown Jewels, in other words, the imperial regalia, and the gem-studded insignia of the various orders of chivalry and diverse virtue made by the court jewellers and goldsmiths in the 18th and 19th centuries. When the First World War broke out in 1914 the Crown Jewels were deposited within the Armoury Chamber, or Arms Palace, in the Moscow Kremlin, for long a treasury in its own right. After the Great October Socialist Revolution in 1917, these treasures, along with famous gemstones, were nationalized and assembled into a collection that has come to be called the Diamond Treasury of the USSR. When diamonds were discovered in Yakutia, in the 1950s, the rare stones found supplemented the Diamond Treasury, which likewise stored brilliant-cut diamonds well displaying the virtuoso skill of Soviet cutters and also more modern works of art executed by Soviet jewellers. The Treasury also boasts a unique collection of gold and platinum nuggets, second to none in the world by virtue of the diversity of their crystalline structure. Among these one could indicate a platinum nugget tipping the scales at almost the full 8 kilograms and the Grand Triangle—Bolshoi Treugolnik—gold nugget which weighs—believe it or not—no less than 36 kilograms!

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.

corundum, USSR.12, Russia.12, gems

corundum, color.4, treatments.6, synthetic corundum.7, gems

corundum, quality.10, gems