Topaz

Thenardite, see Sodium sulfate Thionyl, see Sulflnyl Thorianite, see Thorium dioxide Topaz, see Aluminum hexafluorosilicate Tridymite, see Silicon dioxide Troilite, see Iron(II) sulflde... 

The hardness of a mineral as measured by the Mohs scale is a criterion of its resistance to crushing [Fahrenwald, Trans. Am. In.st. Min. Metall. Pet. Eng., 112, 88 (1934)]. It is a fairly good indication of the abrasive character of the mineral, a factor that determines the wear on the grinding media. Arranged in increasing order or hardness, the Mohs scale is as fohows 1, talc 2, gypsum 3, calcite 4, fluoride 5, apatite 6, feldspar 7, quartz 8, topaz 9, corundum and 10, diamond. 

Hard Materials (7) Quartz, granite (8) topaz (9) corundum, sapphire, emeiy (10) diamond. 

On ihe Mohs scale diamond is 10 and quartz 7. An abemative measure is the Knoop hardness (kgmm ) as measured with a 100-g load typical values on this scale are diamond 7000, boron carbide 2750, corundum 2100. topaz 1340, quartz 820. hardened tool steel 740. 

Stangen-blei, n. bar lead, -eiaen, n. bar iron, rod iron, -gold, n, ingot gold, -kali, n. potash in sticks, stick potash, -kitt, m. stick cement, -kupfer, n, bar copper, rod copper, -lack, m. stick-lac. -schwefel, m. roll sulfur, stick sulfur, cane brimstone, -seife, /. bar soap, -silber, n, ingot silver, -spat, m, columnar barite, -stahl, m. bar steel rod steel, -stein, m. pycnite (columnar topaz), -tabak, m. roll tobacco, -wachs, n. stick wax, stick polish, -zinn, n, bar tin. 

Topas, m. topaz, -fiuss, m. artificial topaz, topasgelb, a. topaz-yellow, topaz. Topasschorlit, m. pycnite (columnar topaz). Topf, m. pot jar, crock top. 

Hardness It is not possible to obtain a reliable figure for the hardness of anodic coatings with either the indentation or scratch methods, because of the influence of the relatively soft metal beneath the anodic film, and the presence of a soft outer layer on thick films. On Moh s Scale, the hardness of normal anodic films lies between 7 and 8, i.e. between quartz and topaz. 

Tin plate, thickness of tin coating on, determination by x-ray spectrography, 148, 149, 157, 158 Tissues, determination of dry weight by absorptiometry, 297-300 Tissue sections, biological, determination of mineral elements in, 301-305 Titanium, as internal standard in vanadium determination, 188 determination by x-ray emission spectrography, 222, 329 trace analysis by x-ray emission spectrography, 163, 225-229 Topaz, as analyzing crystal, 116-118, 220, 318-327 Total reflection, 112, 117... 

FIGURE 14.25 Some of the impure forms of a-alumina are prized as gems, (a) Ruby is alumina with Cr3+ in place of some AIJ+ ions, (b) Sapphire is alumina with Fe33 and Ti43 impurities, (c) Topaz is alumina with Fe3+ impurities. 

Average of reported values for zircon, andalusite, silli-manite, staurolite, topaz, titanite, thortveitite, muscovite, apophyllite, hardystonite, analcite, carnegieite, sodalite, danburite, scapolite, and cristobalite mean deviation 0.02 A. 6 Average for BP04 (1.54 A.) and KHjPO, (1.56 A.). For KjSOi and other sulfates. i For Mg(C104)-6H,0. 

The elucidation of the factors determining the relative stability of alternative crystalline structures of a substance would be of the greatest significance in the development of the theory of the solid state. Why, for example, do some of the alkali halides crystallize with the sodium chloride structure and some with the cesium chloride structure Why does titanium dioxide under different conditions assume the different structures of rutile, brookite and anatase Why does aluminum fluosilicate, AljSiCV F2, crystallize with the structure of topaz and not with some other structure These questions are answered formally by the statement that in each case the structure with the minimum free energy is stable. This answer, however, is not satisfying what is desired in our atomistic and quantum theoretical era is the explanation of this minimum free energy in terms of atoms or ions and their properties. 

The method was then applied in predicting the structure of the orthorhombic crystal topaz, AljSiC>4F. l It was assumed that each aluminum ion is surrounded by four oxygen ions and two fluorine ions at the corners 10 Linus Pauling, Proc. Nat. Acad. Sd., 14, 603 (1928). 

The Principles Determining the Structure of Complex Ionic Crystals.—The success of the coordination method in predicting structures for brookite and topaz has led to the proposal of a set of principles governing the structure of a rather extensive class of complex ionic crystals. 

Fig. 4.—The structure of topaz. The layers are to be superposed in the order abed, with d uppermost. The crosses are the traces of the corners of the unit of structure in the plane of the paper. Large circles represent oxygen, large double circles fluorine, small open circles aluminum, and small solid circles silicon ions.

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