Anorthic

Anorthic (from the Greek an, not, orthos., straight), the name of one of the six systems of crystals, also sometimes called triclinic, as the crystals belonging to it have no two sides at right angles, but are inclined to the surface on which they may be placed in any one of three possible positions. They are not divisible by any plane of symmetry. The felspars crystallising in this system are, for a similar reason, termed plagioclase.