Pseudo re-entrant corner effect

Figure 10.9. Various forms of rock-crystal twinned according to the Japan law from Narushima Island. Nagasaki Prefecture. Japan. The evolution of crystal forms in the order a->b->c is expected as growth proceeds, due to the re-entrant corner or pseudo re-entrant corner effect.

As already explained in Section 7.2, the re-entrant corner effect in its original sense can be expected only when two individuals are perfect crystals, containing no dislocations either in the individual crystals or in the composition plane. In real crystals, the pseudo re-entrant corner effect, by the mediation of dislocations, creates changes in the morphology of the twinned crystal. 

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