Parallel growth and other intergrowth

The appearance of a twin nucleus associated with phase transitions occurs preferentially, in many cases, on free surfaces, internal surfaces of inclusions, boundary surfaces of solid inclusions, or in dislocations where strain is concentrated. 

A mechanical, or secondary, twin is a twin relation that appears due to the displacement of one part of a crystal in a twin relation with respect to the other part, when an external force is applied, and can be regarded as being due to glide. 

After the completion of a series of growth processes forming polyhedral crystals, and a period of cessation of growth, a new stage of growth may recommence from newly supplied solution. In such a case, various intergrowth relations 

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