beryl, emerald, inclusions, India, gems

Gübelin supplements earlier descriptions of Indian emeralds with a detailed examination of four faceted specimens, emphasizing the value of microscopic inclusions for distinguishing their origin. He outlines the discovery and development of emerald deposits in the Aravalli Mountains between Ajmer and Udaipur, particularly near Kaliguman and Bhilwara, where wartime prospecting for beryl and mica revealed emerald-bearing rocks. The emeralds occur in biotite schists associated with hornblende, talcose, and chloritic schists and probable pegmatitic intrusions. Gübelin compares this geological setting with deposits in the Urals, South Africa, and especially Austria’s Habach Valley. His four specimens, weighing 0.70–2.42 carats, display colours comparable to fine Colombian emeralds, although their lustre and visible inclusions vary. Because all were cut stones, he could not examine their original crystal forms directly, but inferred a conventional hexagonal prismatic habit from enclosed negative crystals. Refractive indices range from 1.580 to 1.598, with birefringence of 0.0075–0.009, and specific gravities range from 2.739 to 2.781. These comparatively high values resemble those of emeralds from the Urals and Transvaal but do not independently establish geographic origin. The stones show distinct to strong blue-green and yellow-green dichroism. Lighter specimens exhibit the usual emerald absorption spectrum, whereas darker examples show stronger absorption in the red region. All four remain green through the colour filters tested and are inert under ultraviolet radiation; the two lighter stones exhibit faint dull-red luminescence under X-rays. Gübelin concludes that these physical and optical properties must be supplemented by inclusion evidence. The most characteristic features are liquid-filled negative crystals containing movable gas bubbles, aligned parallel to the emerald’s optic axis. At lower magnification they appear rectangular, square, or comma-shaped; stronger magnification and darkfield illumination reveal their crystalline forms and show that the comma-like outlines arise from groups in which one elongated cavity projects beyond shorter companions. These two-phase inclusions are contrasted with the characteristic three-phase inclusions of Colombian emeralds. A second prominent inclusion type consists of biotite tablets and flakes oriented parallel to the basal plane, often with negative crystals arranged perpendicular to them. Minute actinolite rods and calcite crystals may also occur. The biotite association reinforces the comparison with emeralds from the Urals and Habach Valley, while the combined arrangement and morphology of the inclusions provide the principal distinguishing features described. Through numerous photomicrographs, the article presents an early framework for recognizing Indian emeralds by relating their internal features to their geological environment and measurable gemmological properties.