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III. Four fold axis:
In it, the crystal is repeated four times in the same cycle, i.e. every 90°
IV. Six fold axis:
It is accompanied by repeating the crystal to place it six similar times in
the full cycle, that is, every 60°
3- Center of symmetry:
It represents a middle imaginary point in the crystal around which any
two faces, two edges or two symmetrical solid angles are symmetrical
"meaning that any crystal face that is far from the center of the crystal by
a certain distance must meet it on the opposite side and at the same
distance a similar crystal face and symbolizes the center of symmetry by
the symbol n
Crystal system:
