Screw axes DA screw axis with symbol nm is a combination of an n-fold rotation followed by a translation of a e.g. a 4, axis parallel to z axis involves rotation of 90 followed by translation of 1/4c the operation of 3,axes Symmetry Elements Screw axes rotation about the axis of symmetry by that direction the operation of 6, axes A Floor-Tiling Problem ven Types of Symmetry otoinversion ersion Points symmetry Space symmetry screw axes store th y12 A screw axis with symbol nm is a combination of an n-fold rotation followed by a translation of m/n of the unit cell repeat parallel to the axis. e.g. a 41 axis parallel to z axis involves rotation of 90° followed by translation of 1/4 c. Screw Axes the operation of 31 axes the operation of 61 axes Symmetry Elements: Screw axes rotation about the axis of symmetry by 360°/n, followed by a translation parallel to the axis by b/n of the unit cell length in that direction. A Floor-Tiling Problem Seven Types of Symmetry Points symmetry mirror inversion rotation rotoinversion translation screw axes glide planes Space symmetry Can not restore the left-handed and the right￾handed, only return the equivalent figures Can restore the left-handed and right-handed