Geology Reference
In-Depth Information
(a)
(b)
Figure 11.24.
Polygonal cracking: (a) orthogonal, at Buccleugh, near Johannesburg, South Africa; (b) on
boulder at Tcharkuldu Hill, northwestern Eyre Peninsula, South Australia.
rhomboidal, or polygonal patterns (though some are irregular or crazy, as in crazy paving) defin-
ing thin plates (Fig. 11.24). Various stages in the development of the cracks have been recognised.
The juvenile narrow fractures are linear, and the edges cut through individual crystals, but those
widened by weathering are in detail jagged due to the protection of individual crystals, particularly
of quartz. The polygonal plates range in diameter from 2 cm to some 24 cm, with the average and
