Fig. 26.
Another simple order of figures, and containing within themselves the germ of the most symmetrical combinations, is that of which [Fig. 4] and 5 ([page 136]) are types; they exhibit secondary spiculæ diverging from the principal radii at an angle of 60°.
Around the simple it frequently happens that a secondary and smaller star is arranged, as in [Fig. 6] ([page 136]), the radii of which are intermediate between those of the former. An angle of 30° is, however, of unfrequent occurrence, and it seems probable that in this and similar cases it is the union of two crystals of distinct hexagonal formation.
Fig. 27.
Sometimes it happens that the secondary spiculæ, which we see in [Fig. 4] and 5, are continued down the main radii until they form a contact with each other, as in [Fig. 7] ([page 137]). The star thus enclosed about the centre generally becomes laminated and of great transparency. In other varieties, as in [Fig. 8] ([page 137]), it is intersected by the rays of the secondary or intermediate crystal.
Having traced the elementary principles of these figures to the first formation of a simple nucleus, we will proceed to the consideration of the more compound varieties, in which the nucleus is a conspicuous element of construction.