Symmetry trends of monoelement minerals

The number of the symmetry of each crystallographic class (NSCC) includes the sum of the orders of symmetry axes plus the number of symmetry planes plus one for a center of symmetry, if present. In 94.44% of cases, with increasing of NSCC values, the number of monoelement minerals crystallizing in the respective symmetry classes also increases. The density values Dc (gm/ų) and Dcalc (g/cm³) of the monoelement minerals decrease with the increase of the atomic weight of chemical elements with consecutive or close atomic numbers in the periodic table. The NSCC values show a tendency to decrease with decreasing temperature and pressure of formation of monoelement minerals. At certain NSCC values, the highest the Dc (gm/ų) and Dcalc (g/cm³) of monoelement minerals, the less probable becomes the possibility their polymorphic forms to be established. Polymorphic modifications denser than α-Fe (having Dc = 4.7049 gm/ų and Dcalc = 7.81 g/cm³) have not yet been established. The monoelement polymorphic modifications of As and S, crystallizing in the low symmetry crystal systems, are exceptions to Groth’s law. Most (91.67%) of the monoelement minerals crystallize in the holohedral classes. 2932 of all known 4106 mineral species (71.41%) also crystallize in the holohedral classes of different systems. The data presented suggest that the mineral species in general prefer holohedral classes, having also the highest NSCC values for the respective system. Therefore, the quantitative integral characteristic NSCC is informative in studies of all kinds of mineral assemblages grouped on the basis of different characteristics.