The Occurrence and Distribution of Corundum in the United States,

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U.S. Government Printing Office, 1901 - 98 Seiten
 

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Seite 45 - ... distinct. Most of the bronze corundum is in rough crystals, but some have been found that have the prismatic faces smooth and well developed, and these are often dark, almost black, in color. One crystal of this dark kind, found some years ago, yielded gems f of an inch in diameter.
Seite 9 - A distinction is often made between corundum and emery, many not recognizing emery as a variety of corundum. There are three names in constant use to designate the varieties of corundum: (1) Sapphire, which includes all corundums of whatever color that are transparent to semitransparent; (2) Corundum, including the translucent to opaque varieties of all colors; (3) Emery, which is a mechanical admixture of corundum and magnetite or hematite. It is these last two varieties that are used in the arts...
Seite 99 - LIBRARY CATALOGUE SLIPS. [Take this leaf out and paste the separated titles upon three of your catalogue cards. The first and second titles need no addition; over the third write that subject under which you would place the book in your library.] United States.
Seite 47 - Sept., 1872. 4x2x1^ inches ; part of it is transparent, and several very fine gems could be cut from it, see Plate XII. Another locality in the same county, interesting, though less prominent, is the Mincey mine on Ellijay (properly Elegee) Creek, about 2$ miles northeast of Corundum Hill. Some good ruby corundum occurs here, together with a peculiar brown or bronze variety, known locally as
Seite 28 - In the section the rock at once shows its character as a dark, basic lamprophyre, consisting mainly of biotite and pyroxene. There is a little iron ore present, but its amount is small and much less than is usually seen in rocks of this class. The biotite is strongly pleochroic, varying between an almost colorless and a strong, clear, brown tint.
Seite 39 - NC, various shades of gem ruby corundum have been found. Two of the best rubies of good color that have ever been found at this mine are in the collection of Clarence S. Bement, of Philadelphia; there are also a number of fine ones in the United States National Museum at Washington. Many of the smaller crystals of various shades of pink to red are transparent near the outer surface and near their extremities, and from these small gems can be cut, but few that are worth $100 have been obtained from...
Seite 53 - The only two faces that could be identified were the base c (0001) and the rhombohedron x (3032) which is a new face for corundum. On one crystal two very small faces were observed which were too small to be measured with the contact goniometer, but were probably the faces of a pyramid of the second order. In determining the rhombohedron, ten or more independent measurements were made of c/\x. These varied from 66° to 68°, but approximated closely to 67°, which agrees very well with the calculated...
Seite 74 - ... levels is then the problem of the investigation. HISTORICAL NOTE ON RELATED INVESTIGATIONS While the education of the feebleminded has been given increasing attention since Seguin began his work, the exact measurement of the results of such education has never been accomplished in objective terms. Only within the last few years has any attempt been made to do so with such standardized measurements as are now available. The establishment of special classes in the public schools has raised the...
Seite 74 - It is• necessary, therefore, in making a wheel that it be made of such a temper or grade that when these grains become dull or rounded they will fall away or will be readily removed by a truing tool, leaving fresh sharp •ones exposed.
Seite 16 - ... crystallization would take place first on the outer border of the mass, because here it would cool first. Convection currents would then tend to bring a new supply of material carrying alumina into this outer zone, and when this was reached crystallization would take place and the alumina would be deposited as corundum.

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