ABSTRACT
Solids may be loosely categorized into two groups. Amorphous solids have no longrange order in their molecular or atomic structure. By their nature they are not easily studied, since the powerful analytical methods which are described in Topic A6, for example, are not applicable to such disordered structures. In contrast crystalline solids which consist of ordered three-dimensional arrays of a structural motif, such as an atom, molecule or ion. This internal order is reflected in the familiar macroscopic structure of
crystalline materials, which typically have highly regular forms with flat crystal faces. It is this order and regularity which enables much simpler structural studies of crystalline materials.
