Growth forms of single crystals

If we consider NaOH, KOH, and NaF, which act as mineralizers, to be the solvent components, and other minor amounts of elements such as Fe +and Al to be impurity elements, then the partitioning of these impurity elements is controlled principally by kinetics. The impurity partitioning is related to color, or radiation-induced color, and crystal morphology. 

Some rock-crystals exhibit dog-tooth forms as hexagonal prismatic forms taper off towards the tip of the prism. Some examples are shown in Fig. 10.8. This 

The origin of tapering observed in rock-crystal is basically the same as in the cases of ADP and KDP [11]. In the case of natural rock-crystal, it is suggested that the precipitation of clusters formed in the solution on the growing surface has a similar effect to that of impurity Fe +ions. 

Rock-crystal occurring in vein-type ore deposits grows in ascending hydrothermal solution through cracks in the strata. The flow of solution causes the solute component to be supplied to crystals growing inclined to or perpendicular to the wall of the crack. In laminar flow, the growth rate of the side facing the flow increases compared with the opposite side. In turbulent flow, the situation will be reversed. 

As a result, the section of hexagonal prismatic crystal changes from regular hexagonal (expected when the crystal grows in an isotropic environment) to malformed hexagonal. This variation is also recorded in the crystal as a directional 

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