Minerals chrysoberyl

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. 

Schmetzer, K., Bank, H. GUbelin, E. (1980) The alexandrite effect in minerals chrysoberyl, garnet, corundum and fluorite. Neues Jahrb. Miner. Abh., 138,147-64. 

Alexandrite is a term that should be applied only to naturally dichroic specimens of the mineral chrysoberyl. This stone appears red in one type of light and green in another. The name is in honor of Crown Prince Alexander... 

A gem closely related to ruby and emerald is alexandrite, named after Alexander II of Russia. This gem is based on the mineral chrysoberyl, a beryllium aluminate with the empirical formula BeO AI2O3 in which approximately 1% of the Al3+ ions are replaced by Cr3+ ions. In the chrysoberyl environment Cr3+ absorbs strongly in the yellow region of the spectrum. Alexandrite has the interesting property of changing colors depend-... 

Example 4 BeO/Al203 Two components and P fixed (Figure 8.13). Notice that all the phases can be regarded as combinations of BeO and AI2O3, so we can denote them as B3A, BA, and BA3. From a chemical point of view, the system looks quite similar to Mg0/Al203, but clearly it is very different three separate eutectics are shown none of the compounds has the spinel structure. BeAl204 is the mineral chrysoberyl and has a structure similar to olivine, which is not unrelated to spinel. 

Beryllium is found in some 30 mineral species, the most important of which are bertrandite, beryl, chrysoberyl, and phenacite. Aquamarine and emerald are precious forms of beryl. Beryl and bertrandite are the most important commercial sources of the element and its compounds. Most of the metal is now prepared by reducing beryllium fluoride with magnesium metal. Beryllium metal did not become readily available to industry until 1957. 

The principal minerals of Be arc listed in Table 1, the most abundant being beryl, the only one of commercial significance. Phcnacitc, chrysoberyl, bertrandite and barylitc arc constituents of recently discovered Be-containing deposits future extraction of Be from these ores is currently being considered. The other minerals are not found in sufficient quantities to constitute possible commercial sources of Be. The majority of the ores, including beryl, are complex silicate materials from which it is difficult to extract the metal consequently. Be extractive metallurgy is both complex and expensive. 

The number of oxide type minerals is quite large. Rostov (1956) has identified 160 specific minerals, grouped them into classes (chrysoberyl, spinel, corundum, periclase, etc.), and proposed a classification system. Only a few examples will be discussed here. 

Arfwedson fused the chrysoberyl three times with caustic potash in a silver crucible. Since a portion of the melt corresponding to about 18 per cent of the mineral failed to dissolve in hydrochloric acid, he reported this residue as silica. It is now known that beryllium hydroxide, when freshly precipitated, dissolves readily in hydrochloric acid, but becomes after a time almost completely insoluble in it (17). Therefore, it is probable that Arfwedson s silica was really the beryllium hydroxide. He then precipitated the alumina by adding ammonium hydroxide to the acid filtrate. To satisfy himself of the purity of his alumina, he saturated the alkaline solution with hydrochloric acid until the precipitate dissolved, and added a large excess of ammonium carbonate. Had any glucina [beryllia] or yttria existed in the matter, said Arfwedson, it would have been dissolved by this excess of carbonate of ammonia, and would have fallen when the filtered liquid was boiled till the excess of ammonia was driven off but the liquid stood this test without any precipitate appearing. Arfwedson was evidently unable to detect beryllia here because he had already filtered it off and reported it as silica. When American chemist Henry Seybert analyzed the same mineral in 1824 he found it to contain 15 to 16 per cent of beryllia (22). 

Chrysoberyl, AyJeO which is iso-structural with olivine, exists as the gems alexandrite, (Al,Cr)2Be04, and sinhalite, (Al,Fe)2Be04. Structure refinements of these gem minerals (Farrell et al., 1963), as well as EPR measurements... 

Farrell, E. F. Newnham, R. E. (1965) Crystal-field spectra of chrysoberyl, alexandrite, peridot and sinhalite. Amer. Mineral., 50, 1972-81. 

A number of oxides are economically important ore minerals, such as hematite (iron), chromite (chrome), zincite (zinc), and cassiterite (tin). Some gemstone species are oxides, including corundum (ruby and sapphire), spinel, and chrysoberyl. Corundum is the second hardest natural substance and is used as an abrasive. 

Approximately fifty beryllium minerals occur in nature and over half of these minerals are silicates. Beryllium is mined primarily from these sifi-cates, including beryl, Al2Be3Si60i8, 5 percent (wt.) berylfium, and bertran-dite, Be4(0H)2Si20y, 15 percent (wt.) beryllium. The world resources of beryllium are estimated at approximately 80,000 tons. Other common beryllium silicates include chrysoberyl, BeAl204, and phenacite, Be2Si04. 

Ionic Compounds Chrysoberyl is a transparent or translucent mineral that is sometimes opalescent. It is composed of beryllium aluminum oxide, BeAl204. Identify the oxidation numbers of each of the ions found in this compound. Explain the formation of this ionic compound. 

Beryllium occurs in a number of minerals such as beryllonite (NaBeP04), chrysoberyl (Be(A102)2), bertrandite... 

Precious, or oriental, cat s eye is the rarest and most highly prized form of chrysoberyl it is a green mineral called cymophane the chatoyant effect is due to parallel arrays of pores. 

Hazen RM, Finger IW (1987) High-temperature crystal chemistry of phenakite and chrysoberyl. Phys Chem Minerals 14 426-434... 

Beryllium aluminum silicate, just discussed, is not the only beryllium mineral to occur as precious stones. Chrysoberyl BeAl O with a small amount of iron is also used as a gem. It is usually yeUow, pale green or brown. A transparent variety of chrysoberyl is alexandrite, named after Alexander II, tsar of Russia. It has a green color in daylight but is red in artificial light. 

The Cr " luminescence properties in natural chrysoberyl minerals have been studied as a function of the Cr content as well as impurities such as Fe and V. A competition was foxmd between Cr and V for very low Cr concentration with the vanishing of Cr " emission from Cr " ions located in inversion site. The Fe " ions substitute in mirror site efficiently with a strong impact on the Cr " lifetime of mirror site (Ollier et al. 2015). 

When beryllium is an essential constituent of tin-free minerals and alloys, its presence can be established by isolating beryllium hydroxide and noting the fluorescence reaction with morin (page 124). Silicate-bound beryllium requires fuming with ammonium fluoride for its release. Solution in dilute hydrochloric acid is sufificient in the case of non-ferrous alloys. Chrysoberyl (AlgOg-BeO) must be fused with sodium pyrosulfate. 

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