Three equal axes that are all mutually perpendicular.
Single six-fold rotation axis.
Three unequal axes, two of which are perpendicular.
Three unequal axes that are all mutually perpendicular.
Single four-fold rotation axis.
Three unequal axes with all angles non-perpendicular.
Single three-fold rotation axis.
High-level grouping of crystal systems based on their axial and angular constraints.