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CRYSTALLOGRAPHY (from the Gr. Kpbo Ta...
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See also:CRYSTALLOGRAPHY (from the Gr. Kpbo TaXXO , See also:ice, and -ypachew, to write) , the See also:science of the forms, properties and structure of crystals. Homogeneous solid See also:matter, the See also:physical and chemical properties of which are the same about every point, may be either amorphous or crystalline. In amorphous matter all the properties are the same in every direction in the See also:mass; but in crystalline matter certain of the physical properties vary with the direction. The essential properties of crystalline matter are of two kinds, viz. the See also:general properties, such as See also:density, specific See also:heat, melting-point and chemical See also:composition, which do not vary with the direction; and the directional properties, such as cohesion and See also:elasticity, various See also:optical, thermal and See also:electrical properties, as well as See also:external See also:form. By See also:reason of the homogeneity of crystalline matter the directional properties are the same in all parallel directions in the mass, and there may be a certain symmetrical repetition of the directions along which the properties are the same. When the See also:crystallization of matter takes See also:place under conditions See also:free from outside influences the peculiarities of See also:internal structure are expressed in the external form of the mass, and there results a solid See also:body bounded by See also:plane surfaces intersecting in straight edges, the directions of which See also:bear an intimate relation to the internal structure. Such a See also:polyhedron Grows, many, espa, See also:base or See also:face) is known as a crystal. An example ofthis is See also:sugar-candy; of which a single isolated crystal may have grown freely in a See also:solution of sugar. Matter presenting well-defined and See also:regular crystal forms, either as a single crystal or as a See also:group of individual crystals, is said to be crystallized. If, on the other See also:hand, crystallization has taken place about several centres in a confined space, the development of plane surfaces may be prevented, and a crystalline aggregate of differently orientated crystal-individuals results. Examples of this are afforded by See also:loaf sugar and statuary See also:marble. After a brief See also:historical See also:sketch, the more salient principles of the subject will be discussed under the following sections: I. CRYSTALLINE FORM. (a) Symmetry of Crystals. (b) See also:Simple Forms and Combinations of Forms. (c) See also:Law of Rational Indices. (d) Zones. (e) See also:Projection and See also:Drawing of Crystals. (f) Crystal Systems and Classes. i. Cubic See also:System. 2. Tetragonal System. 3. Orthorhombic System. 4. See also:Monoclinic System. 5. Anorthic System. 6. Hexagonal System Regular Grouping of Crystals (Twinning, &c.). Irregularities of Growth of Crystals: Characters of Faces. (x) Theories of Crystal Structure. II. PHYSICAL PROPERTIES OF CRYSTALS. (a) Elasticity and Cohesion (Cleavage, See also:Etching, &c.). (b) Optical Properties (Interference figures, Pleochroism, &c.). (c) Thermal Properties. (d) Magnetic and Electrical Properties. Additional information and CommentsThere are no comments yet for this article.
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