Split and cracked blocks and slabs - Landforms and Geology of Granite Terrains - page 283

Figure 11.27. Polygonal cracking over the outer shell of a dome in Mariz Quarry, Galicia.

Figure 11.28. Polygonal cracking on several layers at The Granites, Mt Magnet, Western Australia.

some of the vertical cracks can be seen to persist through two or more layers (Fig. 11.28), though
others are discontinuous and are confined to a single layer. At Cassia City of Rocks, Idaho, the
dislocation surface is undulose and the development of polygonal cracking is patchy, possibly
reflecting the discontinuous contact and friction between opposed walls.
Cracking due to shear stresses and consequent changes in planar geometry is well exemplified
at the Mariz quarries near Guitiriz, in northwestern Galicia, Spain where an orthogonal pattern of
fractures has developed on the crest of a dome (Fig. 11.27).