pinacoid

Ancient Greek πινάκιον (pinákion, “slab, tablet”) + -oid.

pinacoid (plural pinacoids)

1. (crystallography) The face of a crystal parallel to two of the axes.
   • 2009 January 16, Juan Manuel Garcia-Ruiz et al., “Morphogenesis of Self-Assembled Nanocrystalline Materials of Barium Carbonate and Silica”, in Science‎, volume 323, number 5912:

     The crystallographic symmetry is initially broken toward dilation symmetry by the splitting of the basal pinacoid or the pseudohexagonal bipyramidal faces of the growing crystal core.

• caponiid, diapnoic, panicoid