Some minerals frequently show split growth, like prehnite, epidote and, perhaps the best example, stilbite. It is a very common phenomenon not only found in quartz. One of the possibilities is that the crystals widen in the direction of preferred growth until their tips split up into several subindividuals. If the crystals have a preferred direction of growth, the numbers and kinds of lattice defects may differ on the various crystal faces and this may cause deviations from the regular growth pattern of the crystals which in turn may lead to peculiar shapes. Parts of the lattice can get displaced slightly and as a result peculiar patterns develop on the crystal's faces.
Perfectly clear quartz full#
Natural crystals are full of imperfections and their crystal lattices deviate from the ideal regular geometry.
This is merely a practical consideration and if someone else decides to call a specific growth form a variety, I will not object to this. So when a jewel is cut from an amethyst scepter quartz all that will be left is an amethyst and the scepter quality will be gone. A color variety does not loose any of its specific qualities when cut, but a form variety will. I do not call growth forms varieties, for the following reason: even a small, incomplete fraction or sample of a crystal can still be identified as a specific color variety, but this does not work for growth forms. Some authors distinguish color varieties and form varieties, and growth forms would be considered as form varieties. Included are some phenomena in quartz which are not related to the actual shape of the crystals, but to other aspects of their visual appearance and which are an imprint of changes in the environment. This section covers those aspects of quartz morphology that are not covered in the descriptions of crystal forms, habits, and twinning, and also covers those related to the overall appearance of crystal aggregates. I've kept a copy of the old version for comparison. This chapter has been partially rewritten and some of the definitions have been changed because in my view they were inconsistent.
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