The Collaborative International Dictionary of English v.0.48:

octahedral \oc`ta*he"dral\ ([o^]k`t[.a]*h[=e]"dral), a. [See
   octahedron.]
   Having eight faces or sides; of, pertaining to, or formed in,
   octahedrons; as, octahedral cleavage; an octahedral crystal.
   [1913 Webster]

   octahedral borax (Chem.), borax obtained from a saturated
      solution in octahedral crystals, which contain five
      molecules of water of crystallization; distinguished from
      common or prismatic borax.

   Octahedral iron ore (Min.), magnetite.
      [1913 Webster]