## A system of crystallography, with its application to mineralogy |

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acute angles replaced Antimonial Augite axis belonging calculation Class Cleavage combination Copper cotangent crystal crystallographers cube denoted east meridian east zone edge to axis edges replaced eidogens equal equator Fluorspar Formula Genus given goniometer half the angle hedron hemihedral forms hemioctahedron homohedral horizontal inclination incomplete prism incomplete pyramid iPMT Iron Pyrites log cot long edge middle edge minerals Model 15 Model 26 MT.PM.PT north meridian oblique obtuse octahedral octahedron octant P_MT P+M_T plane angle planes of Model Prismatic System problem produce quadratic octahedron rhombic dodecahedron rhombic prism rhombohedron rhombus right angles scalene octahedron scalenohedron short edge side solid angles symbol System of Crystallisation tangent terminal edge tetrahedron three axes tion tripolar normal Twice this product vertex vertical planes Z'nw Zne Znw Znw normal Zse Zsw

### Popular passages

Page 96 - ... experience a very marked difference, if comparatively trying in this way any two subsequent members of the above scale, and thus the difference in their hardness will be easily perceived. A short practice is sufficient for rendering these perceptions more delicate and perfect so that in a short time it is possible to determine differences in the hardness very much less than those between two subsequent members of the scale. "Upon these observations is founded the application of the scale, the...

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 96 - ... 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 124 - After remarking that the mathematician positively knows that the sum of the three angles of a triangle is equal to two right angles...

Page 96 - ... process alone is not sufficient, if we intend to make a more sure and extensive application of the characters that may be taken from hardness, than that which has hitherto been common in Mineralogy. But if we take several specimens of one and the same mineral, and pass them over a fine file, we shall find that an equal force will everywhere produce an equal effect, provided that the parts of the mineral in contact with the file be of a similar size, so that the one does not present to the file...

Page 3 - A rhomboid is that which has its opposite sides equal to one another, but all its sides are not equal, nor its angles right angles.

Page xxiii - In this case, both hardness and specific 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...

Page 96 - ... nearly agreeing in form and size, and also as much as possible in the quality of their angles. From the resistance these bodies oppose to the file, and from the noise occasioned by their passing over it, we argue with perfect security upon their mutual relations in respect to hardness. The experiment is repeated with all the alterations thought necessary, till we may consider ourselves arrived at a fair estimate, which is at last expressed by the number of that degree with which it has been found...

Page 96 - It is necessary also that the force applied in this experiment be always the least possible. "Every person, however little accustomed, will experience a very marked difference, if comparatively trying in this way any two subsequent members of the above scale, and thus the difference in their hardness will be easily perceived. A short practice is sufficient for rendering these perceptions more delicate and perfect so that in a short time it is possible to determine differences in the hardness very...

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.