Orthorhombic Symmetry : Symmetry with respect to three mutually orthogonal planes. There are 9 independent elastic parameters for an orthorhombic material. Olivine crystals are orthorhombic. 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}