which each of the angles of the cube is unsymmetrically replaced by three faces of the dyakisdodecahedron, and
hence
or fig. 23, in which the pentagonal-
dodecahedron has its trigonal angles replaced by the faces of the octahedron, consequently with the sign
Figure
24 represents the same combination but with greater predominance of
the laces of the octahedron, the crystal being bounded by eight
equilateral and twelve isosceles triangles.
II. Tetragonal System.—This
system has three axes at right angles, two of them equal and one
unequal. The last is the principal axis, and when it is brought into a
vertical position the crystal is said to be placed upright. Its ends
are named
