Beryl

BERYL (from the Greek word "beryllos", the ancient name of the precious stones, which were used for the optical glasses * EN: beryl; DE: Beryll; FR: beryl; ES: berilo; RU: берилл) is the mineral of the sub-class of the cyclic silicates, Be3Al2[Si6O18]; it contains 14.1% of the BeO. There are characteristic the impurities of Na, Cs, Rb, Li, Fe2+, Fe3+, Mg, Mn, H2O, He; rarely Cr3+, Sc, Ca. It crystallizes into the hexagonal crystal system. The major structural motif is the hexagonal rings of the [Si6O18], which are situated one above the other in the form of the columns with the hollow vertical channels within them; the rings are interconnected by the columns of the Be-tetrahedra and Al-octahedra. The impurities, which exist within the composition of beryl, replace the Be or Al elements; the large cations of the alkali metals and water situate themselves within the channels.

They distinguish the 3 types of beryl: the t-beryls, within which the Li- ions and partly the Mg2+ ions occupy the tetrahedral positions of the Be2+ ions; the o-beryls, which are containing the Fe2+, Fe3+, Mg2+, Mn2+ cations within the octahedral positions, namely, instead of the Al3+ cations; the n-beryls of the theoretical composition. According to the content of alkalies and Li, they distinguish the alkali-less, sodium, sodium-lithium, and lithium-cesium varieties.

There are characteristic for the beryls the well-formed crystals of the prismatic, acicular, less often tabular habitus, often of the significant size. The largest of the crystals, which are known within the world, is the crystal of beryl from the Madagascar island (the length is 18 metres, the diameter is 3.5 metres, the mass is 380 tonnes). There are characteristic the pseudo-monocrystals (the aggregate intergroughths of the individuals with the common external faceting). The pure beryl is colourless; the colouration of beryl is determined by the composition of the impurities. The bluish-green tints are associated with the Fe2+ and Fe3+ impurity, the saturated-green ones with the Cr3+, the yellow ones with the Fe3+, the pink ones with the Mn2+. The hardness is 7.5-8. The density is 2650-2750 kilograms per cubic metre.

Beryl forms itself within the granitic pegmatites, greisens, within the associated with them quartzous veins and hydrothermal formations of beryl, which are formed of pegmatites, which are represented mainly by the sodium, sodium-lithium, and lithium-cesium varieties. For the early high-temperature mineral associations of the greisen deposits, there are typical the beryls of the o-beryl type. The least quantity of the impurities is characteristic for the beryl from the quartzous veins, quartz-muscovitic and fluorite-muscovitic greisens. Within the relatively low-temperature shallow deposits, which are transitional from the greisen to the late-alkaline hydrothermal, there again appear the beryls, which are enriched with the Na, Mg, Fe impurities. Beryl is one of the main minerals of the beryllium ores. The transparent, beautifully coloured varieties of beryl are the precious stones: pale blue (aquamarine), saturated-green (emerald), golden-yellow (heliodor), pink (vorobyevite, morganite), blue (maxixe). There are best known the pegmatitic deposits of beryl: Bernik Lake (Canada), Black Hills (USA), Minas Gerais, Boa Vista (Brazil). The interspersed ores with small and fine particles are beneficiated by flotation according to the acidic or alkaline schemes. There have got the widest distribution the alkaline schemes. The crushed and deslimed ore is processed by alkali, is contacted during the heating of up to 80 degrees Celsius with the fatty acidic collector, with the subsequent flotation of beryl. See also the "Beryllium ores" article.