engleski

Symmetry in the world of minerals

Symmetry is very common in nature, even minerals are not an exception. Moreover, from the very definition of minerals, which states that a mineral is a naturally occurring homogeneous solid, formed by geological process, with a definite (but generally not fixed) chemical composition and a highly ordered atomic arrangement, it is clearly visible that symmetry is a very important characteristic of each mineral. The question is: Why does symmetry occur in minerals? The answer to that question is not a very simple one but it can be said that symmetry is internal, that it is a result of an ordered geometrical arrangement of atoms in the crystal structure. If a mineral grows freely it becomes a crystal whose faces are an external reflection of its internal symmetry. Internal symmetry is the result of the atoms' tendency to be in the state of the lowest possible energy. The main symmetry operations in minerals are: rotation, reflection, and inversion, and each of these operations is performed by three main elements of symmetry, which are: axis of rotation, mirror plane and center of symmetry. Symmetry elements may be present in several different combinations. There are 32 possible combinations of symmetry elements on crystals. These 32 combinations define the 32 crystal classes which can be grouped in six (seven) crystal systems.

symmetry; minerals

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