Phenacite

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. 

Betyllium, because of its small size, almost invariably has a coordination number of 4. This is important in analytical chemistry since it ensures that edta, which coordinates strongly to Mg, Ca (and Al), does not chelate Be appreciably. BeO has the wurtzite (ZnS, p. 1209) structure whilst the other Be chalcogenides adopt the zinc blende modification. BeF2 has the cristobalite (SiOi, p. 342) structure and has only a vety low electrical conductivity when fused. Be2C and Be2B have extended lattices of the antifluorite type with 4-coordinate Be and 8-coordinate C or B. Be2Si04 has the phenacite structure (p. 347) in which both Be and Si... 

The tetrahedral Si()44 ion is known as the orthosilicate ion. It can be regarded as the fundamental unit in the structures of most complex silicates. Several minerals including phenacite, Be2Si04, and willemite, Zn2Si04, contain this ion. Both of these minerals have tetrahedral coordination of Si044- units around the metal ion ... 

Cobalt zinc silicate blue phenacite, formula and DCMA number, 7 347t Co-base superalloys, 13 503, 525-527 composition of, 13 526 Cobbing services, magnetic drums used in, 15 445-446 Cobb test, 13 101 Cocaine, 2 74, 79, 80, 108 economic aspects, 2 108 Cocamide DEA, function as ingredient in cosmetics, 7 829t... 

Just as P043- is known as the orthophosphate ion, the tetrahedral Si044- ion is called orthosilicate. This tetrahedral monomeric unit is found in several minerals (e.g., phenacite, Be2Si04, and willemite, Zn2Si04). In both of these minerals, the metal is surrounded by four oxygen atoms in Si04 units arranged tetrahedrally around the metal ... 

Ge nitride, GesN4, is formed as a black solid from Ge and ammonia at 650 °C, or by heating the imide [Ge(NH)2] at 400 °C. It exists in two forms, both of which have a phenacite-type structure. It decomposes to the elements at 900 °C. GesNq is stable to air and insoluble in HCl, HNO3, H2SO4, and NaOH aqueous. At 700 °C, reaction of Ge3N4 with H2 results in Ge and NH3. 

Si04 (olivine) Li2 M0O4 (phenacite) Mg2 Si04 (spinel) 130 870... 

The material considered in the third study was /3-S13N4. The implanted atoms we dealt with here were Fe, Mo and Hf located at an interstitial site. The crystal structure of, d-Si3N4 is hexagonal phenacite-like, and the unit lengths... 

Li2BeF has a hexagonal unit cell (space group r5) isotypic with phenacite (6). This structure shows no phase transitions between room temperature and T (3, 4, 7), but exposure to traces of moisture at elevated temperatures causes decomposition to LiP and BeO (7, 8). Metastable forms have been reported (4) but not confirmed or identified. 

The thermal stability of stains and oxides is particularly important in view of the high processing temperatures and therefore oxide host-lattices with spinel-, corundum-, rutile-and silicate-phases are favored as well as zircon, phenacite, garnet and sphene structures. 

Alternatively, one can treat silicates as closest packed arrays of oxide ions with Si ions fitting into tetrahedral holes and other metal ions fitting into either tetrahedral holes as in phenacite or octahedral holes as in olivine. (See Fig. 7.3 for the alternative ways of describing olivine.) Transition metal ions in these structures behave as they do in complexes Olivine gets its name from the greenish color caused by partial substitution of Fe " for Mg ions in the octahedral holes. The hexa-aquairon(II) ion has a similar green color. The hue of garnets also comes from transition metal ions. 

The phenacite structure (p. 811) of Li2BeF4 may be described either as containing tetrahedral BeF " ions or, since both Li" and Be " are tetrahedrally coordinated, as a 3D ionic structure. 

Unlike sulphur oxygen seldom forms more than two covalent bonds in simple molecules or ions. There are numerous ionic crystals in which 0 forms three bonds (rutile, phenacite, etc.). In salt hydrates where H2O is bonded to a metal atom, (a), or in hydroxides where OH bridges two metal atoms, (b), the bonds to the metal atoms presumably have appreciable ionic character, and this is probably also true in AlOCl (p. 408) and [Ti(0R)4] 4 (p. 942). Three equivalent (covalent )... 

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