Morphology of crystals - the problems

The morphology of crystals is the central theme of this book. Our intention is to present systematically the fundamental concepts that allow us to analyze the factors that determine the various forms of crystals. We may then deduce and analyze the phenomena and processes that we cannot observe in situ, such as those occurring in the depths of the Earth or in the animate world. 

When there is no distortion in the structure or no change in orientation throughout a crystal, we refer to the structure as a single crystal. A solid consisting of many single crystals with different orientations is called a polycrystalline aggregate. There are also polycrystalline aggregates of multiple phases, as in metals, rocks, and ceramics. 

transparent single crystals of centimeter size are used for facet cutting in jewelry making. 

To do this, we must first investigate the origin of the variations in morphology exhibited by the same single crystal. For example, a single crystal might exhibit a polyhedral form bounded by flat crystallographic faces, a hopper or skeletal form bounded by faces with a step-wise depressed center at a face, or a dendritic form (see Fig. 2.1). 

On crystal faces bounding a polyhedral crystal, step patterns resembling the contour lines on a topographic map or striations in one direction are observable depending on the nature of the face. These show the process of crystal growth or dissolution at an atomic level, and are referred to as the surface morphology or surface microtopography. 

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