Dr. Chanchal Sarbajna
Head, Mineralogy-Petrology-Geochemistry Group, AMD, Department of Atomic Energy, Hyderabad
As a school student I was required to memorize the periodic table in my Chemistry class; I guess many of this generation students also may be doing the similar drill. Later when I joined as Geologist, I had to again brush up on my Chemistry but in a more detailed way. One of the mineral, I had to work on was Beryl. As the name suggests, the beryl mineral consists of element beryllium (Be; Z=4).
Beryllium (Be) is known to have the second lowest density compared to common structural light metal alloys such as magnesium, aluminium and titanium. It has high thermal conductivity and specific heat and hence, has excellent specific heat dissipation compared to other metals. Beryllium has one of the highest melting points out of the light metals. It is nonmagnetic and resists attack by concentrated nitric acid. Beryllium resists oxidation when it exposed to air. All these unique characteristics make Beryllium a
suitable material for application in Missiles and Light weight spacecrafts.
The more common beryllium containing minerals include Beryl (Be3Al2Si6O18; 10-14% BeO), Chrysoberyl (BeAl2O4; 17- 20% BeO), Phenakite (Be2SiO4; 46% BeO) and Bertrandite [Be4Si2O7(OH)2; 42% BeO]1. Beryl and bertrandite are the two major ores of beryllium2. Beryl which is one of the most viable ores of beryllium are confined largely to igneous rocks like granitic pegmatite3 where hot, mineral rich fluids circulate through cavities in the Earth's crust. The gradual cooling of these fluids within the
pegmatite veins allows Beryl crystals (Fig.1) to grow, into huge hexagonal shaped crystals. Beryllium is used in the production of neutrons (9Be4 + 4He2 -- 13C6 --12C6+ 1n0) for splitting of uranium atoms in nuclear reactors besides used as reflector or moderator of neutrons. Beryllium is also used in X-ray tubes as optical windows. These are ultra-thin and can withstand high temperatures which make them suitable in high-end sophisticated instruments such as X-ray fluorescence spectrometers (XRFS) and X-ray diffractometers (XRD). These equipments have tremendous applications in geology, metallurgy, material science, ceramic and pharma industry etc. to characterize different materials chemically and structurally. Beryl occurs as hexagonal crystals and this crystalline nature can be observed by X-ray diffractometer (XRD) as shown in
Fig. 2 which shows peaks characteristic to the Beryl mineral. Stereo-microscopically observed crystals of beryl were also studied under Scanning Electron Microscope (SEM) (Fig. 3). Such crystals exhibit euhedral hexagonal prismatic forms.
Skilled gem cutters transform mineral crystals in to sparkling gems. The procedure varies from mineral to mineral and the desired cuts. There are mainly 3 types of cuts- Cabochon, step cut and brilliant cut. Rounded surface of Cabochon enhances opaque and transluscent stones as well as optical effects such as stars and cats eye (Fig. 4). The flat surface of step cuts allows abundant light to enter bringing out the colour of emeralds, rubys and other intensely coloured stones (Fig.5). The facet of brilliant cuts refracts
light which shows of diamonds and other fiery gems (Fig.6).
Beryl is a treasure trove of precious gemstones. From the vibrant green of emeralds to the azure blue of aquamarines, beryl’s diverse varieties captivate us with their beauty. Precious forms of beryl are emerald (green due to chromium impurities; Fig.7), aquamarine (blue due to iron impurities; Fig.8), morganite (pink due to manganese impurities), heliodor (yellow due to iron impurities; Fig.9), bixbite (red due to trace amounts of manganese; Fig.10) and the purest form of beryl called goshenite (colourless).
Beryllium being light weight is a new generation preferred alloy in the field of aerospace & defence industries. Its uniqueness lies in its properties having high melting point (~1289°C), resistance to acid and oxidation making it ideal for use in missiles and space crafts amongst many other uses. Beryllium is also creating a niche in the medical field with its use in imaging medical devices. Its transparency exhibits beautiful colours and brilliance making them excellent choice for precious stone embedded jewellery. Such
is its current impact and future potentials making Beryllium to stand out as a Gem of a mineral.
References:
1. Černý, P. (2002). Mineralogy of beryllium in granite pegmatites, Pp. 405-444 in: Beryllium: Mineralogy, Petrology and Geochemistry, (E.S. Grew, editor). Reviews in Mineralogy & Geochemistry, 50. Mineralogical Society of America and Geochemical Society, Washington, D. C.
2. Deer, W. A., Howie, R. A. and Zussman, J. (2013). An introduction to the rock-forming minerals. The mineralogical society, London, 498 p.
3. Sarbajna, C et al. (1999). Mineralogy and geochemistry of alkali beryl from the rare metal bearing pegmatites of Marlagalla-Allapatna, Mandya district, Karnataka. Journal Geological Society of India, v..54, pp..599-608.
4. Renfro et al.(2023). Microfeatures of beryl. Gems and gemological Institute of America, v.59(4), pp. 484-485.
