A type of quartz twinning in which the two or more intergrown parts are related as by a rotation of 180 degrees about the common Z = c axis. The separate individuals of the twin are either all right handed or all left handed. Electrical twinning cannot be detected by optical tests, but can be recognized by etching, X-ray study, pyroelectric tests, or the distribution of the x 5161 or s 1121 faces.