Triangular dendrites of LiAlSiO₄–SiO₂: evolution between threefold- and sixfold-symmetric morphologies

A special kind of triangular dendrite of LiAlSiO₄–SiO₂ (or Li_1−xAl_1−xSi_1+xO₄, 0 ≤ x ≤ 1) in matt glaze has been observed by DIC (differential interference contrast) microscopy. This triangular dendrite is β-quartz with a sixfold-symmetric structure. For polyhedral crystals, a crystal with threefold-symmetric structure prefers to develop a hexagonal prismatic habit rather than a trigonal prismatic habit, because a trigonal prism has a higher surface energy than a hexagonal prism. However, for dendritic crystals, a special kind of triangular dendrite, with a pattern formed by the aggregation of many small triangles, can develop. As supercooling decreases, β-quartz can develop a series of morphologies with different surface energies, from snowflake-shaped dendrite to triangular dendrite, and finally to a polyhedral crystal in the form of a hexagonal prism. This series of crystal morphologies shows a morphological evolution from dendrite to polyhedral crystal, and also shows a morphological evolution between sixfold and threefold symmetries.