A System of Crystallography: With Its Application to Mineralogy (Google eBook)

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R. Griffin, 1841 - Crystallography - 469 pages
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Page 94 - ... expressed by the number of that degree with which it has been found to agree nearest, the decimals being likewise added, if required. The files answering best for the purpose are fine and very hard ones. Their absolute hardness is of no consequence ; hence every file will be applicable, whose hardness is in the necessary relation with that of the mineral. For it is not the hardness of the file with which we have to compare that of the minerals, but the hardness of another mineral, by the medium...
Page xxvi - The same number of atoms combined in the same way produce the same crystalline form, and the same crystalline form is independent of the chemical nature of the atoms, and is determined only by their number and relative position.
Page 94 - First we try, with a corner of the given mineral, to scratch the members of the scale, beginning from above, in order that we may not waste unnecessarily the specimens representing lower members. After having thus arrived at the first, which is distinctly scratched by the given mineral, we have recourse to the file, and compare upon it the hardness of this degree, that of the next higher degree, and of the given mineral. Care must be taken to employ specimens of each of them nearly agreeing in form...
Page xxiii - ... gravity are prominent characters, and exclude the individual at once from the first and third, but not from the second class : with the characters of this class, its other properties also perfectly agree. Hence the individual belongs to the second class. Comparing the properties of the individual with the characters of the orders in the second class ; hardness and specific gravity will be found too great for the order Haloide ; hardness too great for the orders Baryte and Kerate ; both of them...
Page 93 - Holohedral Forms' of any system are those which possess the highest degree of symmetry of which the system admits. ' Hemihedral Forms ' are those which may be derived from a Holohedral Form, by supposing half of the faces of the latter omitted according to a certain law.
Page 127 - The division of one quantity by another is frequently represented by placing the dividend over the divisor, with a line between them, in which case the expression is called a fraction ; thus, £)”vjsor) '-i , signifies a divided by b ; then a is the numerator and b the denominator of the fraction.
Page xxii - Gravity must be tried with proper accuracy, and expressed in numbers. It is sufficient, however, to know the latter to one or two decimals. The specific character requires these data ; they are also of use in the characters of the classes, orders, and genera. After this examination, the Characteristic may be applied, and it will at the same time point out what other characters are still wanting ; so that a mere inspection of the mineral, or a very easy experiment, as, for instance, to try the streak...
Page 3 - If a side of any triangle be produced, the exterior angle is equal to the two interior and opposite angles ; and the three interior angles of every triangle are equal to two right angles.
Page xxiii - ... given individual is now carried through the subordinate characters of the classes, orders, genera, and species, one after the other, comparing its properties with the characteristic marks contained in the characters of these systematic unities. From their agreement with some, and their difference from other characters, we infer, that the individual belongs to one of the classes, to one of the orders, to one of the genera, and to one of the species. Having advanced in this manner to the character...
Page xxiv - In regard to the individual, which is to be determined, all the characteristic marks constituting the Character of the order Ore, may be divided into two parts. The first part contains those which refer to the individual ; the second those which do not ; the last evidently cannot be decisive. But with the first, all the properties of the individual concur. These properties agree consequently with the whole character of the order, as far as it is applicable to the individual, and determine it to belong...

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