Symmetry by rotation of 60 around one axis, the 6-fold symmetry axis. Hexagonal symmetry and cylindrical symmetry are equivalent for the elastic properties. There are 5 independent elastic parameters in hexagonal symmetry systems. See: Cara (2002)
Peter Bormann, Keiiti Aki, William H. K. Lee, and Johannes Schweitzer (Compilers and Amenders), Glossary of Terms Interest to Earthquake and Engineering Seismologists (Version 1), Publication records from external use of GFZ scientific infrastructure, Germany 2011. http://gfzpublic.gfz-potsdam.de/pubman/item/escido c:56137:3/component/escidoc:56143/Glossary_rev1.pd f, (ND/ Erthq - Amer) {980}