Beryl hardness

The discovery of beryllium in 1798 followed an unusual train of events. The mineralogist R.-J. Haiiy had observed the remarkable similarity in external crystalline structure, hardness and density of a beryl from Limoges and an emerald from Peru, and suggested to L.-N. Vauquelin that he should analyse them to see if they were chemically identical. As a result, Vauquelin showed... 

Emerald Gemstone A variety of beryl Very hard... 

The correct composition of beryl and the emerald was not known until the close of the eighteenth century, when the Abb6 R.-J. Hauy pointed out the remarkable similarity in crystalline structure, hardness, and density of a beryl from Limoges and an emerald from Peru, and N.-L. Vauquelin discovered that they both contain as an essential constituent glucinum, or beryllium, and that the emerald, except for the presence in it of a little chromium, has the same composition as the beryl (25,27,91). 

CHRYSOBERYL. The mineral chrysoberyl. an aluminaie of hery Ilium corresponds to the formula BeALO. , crystallizes in the orthorhombic system with both contact and penetration twins common, often repeated resulting in ro.setted structures. Hardness. 8.5 specific gravity. 3.75 luster vitreous color various shades of green sometimes yellow. A variety which is red by transmitted light is known as alexandrite. Streak colorless transparent to translucent, occasionally opalescent. Chrysoberyl also is known as cymopbane and golden beryl. 

Beryllium Beryllium was first detected in 1798 in the gemstones beryl and emerald (BesA SigOis) and was subsequently prepared in pure form in 1828 by the reduction of BeCl2 with potassium. It is obtained today from large commercial deposits of beryl in Brazil and southern Africa. Though beryllium compounds are extremely toxic, particularly when inhaled as dust, the metal is nevertheless useful in forming alloys. Addition of a few percent beryllium to copper or nickel results in hard, corrosion-resistant alloys that are used in airplane engines and precision instruments. 

Emerald is a variety of beryl, a beryllium silicate, with a hardness of 7.5 to 8. It has a beautiful deep green color, and it is one of the most expensive gems, sometimes outranking diamond in value. The green color results from small amounts of chromic oxide (Cr203). The oldest emerald mines were in Egypt near the Red Sea, but the best emerald mines today are in Colombia. There are others in Brazil, Pakistan, and Africa synthetic emeralds of excellent quality have also been manufactured. 

Aquamarine, like emerald, is a transparent variety of beryl, or beryllium silicate. Its light blue to blue-green color results from small amounts of iron in the crystal. Like most beryl stones, it measures 7.5 to 8 on the Mohs hardness scale. Most aquamarine gemstones come from Brazil. 

Beryllium is found in emeralds, which are a variety of the mineral beryl. Perhaps the best-known alkaline-earth metal is calcium, an important mineral nutrient found in the human body. Calcium is essential for muscle contraction. Bones are made up of calcium phosphate. Calcium compounds, such as limestone and marble, are common in the Earth s crust. Marble is made almost entirely of pure calcium carbonate. Because marble is hard and durable, it is used in sculptures. 

Properties Fine, hexagonal, hard, refractory crystals attacked vigorously by strong, hot alkali solutions forming methane gas and alkali beryllate. D 1.91 decomposes above 2100C. 

Historical. — In 1797, HaQy, a mineralogist, found that the minerals beryl and emerald had the same physical structure, hardness, and specific gravity. He asked Vauquelin to make a chemical analysis to see if they were not of the same composition. In the course of the analysis Vauquelin found that while these two minerals were of the same composition they both contained an oxide very similar to alumina but differing from it in the fact that it was precipitated from its KOH solution by boiling. Further study showed other peculiarities its salts had a sweet taste its hydroxide was soluble in dilute ammonium carbonate and its sulfate formed irregular crystals but no alum with KjS04. 

Alkoxyl group exists in the non-polar position of some xanthates and dithiophosphates, which have properties similar to those of alkyl group and produce more froth. For example, etheralkyl carboxylate (ECA), R ,-(OC2H4) 2-OCH2COOH, has been reported as a collector where ni is Cg ig chain and W2 is the number of alkoxyl groups (0-16). Since its Ca or Mg salts with ni = 10, 12, 14, 17 and h2 = 10, 20 30 are soluble in water, ECA is suitable under hard water and low pH (<6) conditions for the flotation of calcium or magnesium minerals, chalcopyrite and beryl with better selectivity. FloatabiUty of Ca minerals is found to linearly decrease with n values and increase with h2 values. 

Finally, we shall return to the case of beryl, which contains two metal atoms. Formula (34) is not directly applicable. Moreover, the obtained results permit the conclusion that the ionicity of Ail-0 bonds is greater than that of Be-0 bonds. In both cases, the electronegativity differences are practically the same (1.8 and 1.9), but the aluminum atom is more polarizable. Consequently, the hardness is conditioned by the ionicity of Be-0 bonds, which are the strongest. If we assume that the environment of Be atoms is practically the same... 

Figare 3.15. Knoop hardness anisotropy on (a) (0001) and (b) 1010 planes of beryl, BejAljSiftOig, from reference (22). 

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