Crystal belongs to the tripartite system. Why does it crystallize into a hexagonal cone at one end or a hexagonal column at both ends?

The crystal belongs to hexagonal system. The crystal is prismatic, with a hexagonal cone, the cylinder has horizontal stripes, and amethyst often has angular stripes. In nature, crystals are often produced in groups with beautiful shapes. Well-crystallized crystals usually have a good herringbone fracture with parallel ridges; In amethyst and heat-treated topaz, most of them are uneven sheet fractures. Crystal specific gravity: 2.56-2.66g/cm3. This means that the weight of a certain volume of crystals is 2.56-2.66 times that of the same volume of water. Bulk crystals may have a slightly higher density.