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may have a number of levels of symmetry that intersect in different
directions, for example, a cubic crystal of halite is characterized by
containing nine levels of symmetry

2- The axis of symmetry
It is defined as an imaginary line passing through the center of the crystal.
If it is rotated around it a full 360 degrees, it represents the same position,
or the appearance of the face, edge, or solid angles is repeated a number
of times, so that it is not possible to differentiate between the first
position and the other new conditions, and for this it is called a axis of
rotational symmetry.
The axis may be perpendicular to some facets of the crystal and parallel
to the edge of it. The degree of symmetry of the axis is determined by the
number of similar positions of the crystal in the complete cycle. The
types of rotational axis of symmetry are as follows:

I. Two fold axis:

In which the crystal is repeated twice in the full cycle, that is, every 180°

II. Three fold axis:

And in which the similar crystal is repeated three times in the full cycle,
that is, every 120°