From Online Dictionary of Crystallography

Orthohexagonal (Fr). Orthohexagonalen (Ge). Ortoesagonale (It). 直方六方 (Ja). Ortohexagonal (Sp).

The hexagonal lattice is frequently referred to an orthorhombic C-centred cell called orthohexagonal, whose volume is twice that of the conventional P cell. Three choices of the orthohexagonal cell are possible:

  • C1, basis vectors change a, a+2b, c;
  • C2, basis vectors change a+b, -a+b, c;
  • C3, basis vectors change b, -2a-b, c.

The hexagonal symmetry is reflected in the metric specialisation of the orthohexagonal cell, which has b = a31/2. As a consequence, an orthorhombic crystal with conventional cell of type oC and b = a ratio close to 31/2 has a pseudo-hexagonal lattice.

See also

  • Chapter 1.5 of International Tables for Crystallography, Volume A, 6th edition