Interfacial angles, constancy

A theory usually involves some idea about the structure of the universe, whereas a law may represent a summarizing statement about observed experimental facts. For example, there is a law of the constancy of interfacial angles of crystals. This law states that when the angles between corresponding faces of various crystals of a pure substance are measured, they are found to have the same value. This law simply expresses the fact that the angles between corresponding faces on a... 

These observations led to the concept of a unit cell. Haiiy was able to build realistic models of calcite crystals by stacking rhombohedral building blocks of uniform size (each with interfacial angles of 75°). Clearly, the interfacial angles are important dimensions of the exteriors of crystals. The Law of the Constancy of Interfacial Angles was first proposed by Steno. It states that in all crystals of a givpn... 

Constancy of Interfacial Angles, Law of In all crystals of a given type from a given compound, the angles between corresponding faces have a constant value. This law applies to one particular form if the crystal is polymorphous. 

Figure 27.24 The constancy of interfacial angles, (a) Section of an ideal quartz crystal, (b) and (c) Possible shapes of the crystal section.

De solido intra solidum naturaliter contento Dissertationis Prodromus, Florence, 1669 Ost-wald s Klassiker, 1923, ccix he did rather more than establish the constancy of interfacial angles Hey, Nature, 1958, clxxxii, 278. 

Law of constancy of interfacial angles In all crystals of the same substance (in the absence of polymorphism), angles between corresponding faces are identical. Rhodes G (1999) Crystallography made crystal clear a guide for users of macromolecular models. Elsevier Science and Technology Books, New York. 

The science of geometric crystallography was concerned with the outward spatial arrangement of crystal planes and the geometric shape of crystals. Workers of that day arrived at three fundamental laws (a) the law of constancy of interfacial angles, (b) the law of rationality of indexes, and (c) the law of symmetry (14). 

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