(Hemihedral, Pediad).
Crystals of this class are devoid of any elements of symmetry. All the
forms are pedions, each consisting of a single plane; they are thus
hemihedral with respect to crystals of the last class. Although there
is a total absence of symmetry, yet the faces are arranged in zones on
the crystals.
Examples are calcium thiosulphate (CaS2O3.6H2O) and hydrogen strontium
dextro-tartrate ((C4H4O6H)2Sr.5H2O); there is no example amongst
minerals.