Several little deformed sedimentary and volcanic rocks may contain structures that closely resemble mylonitic structures. Two examples are shown in this section. Low grade metasedimentary wackes containing detrital quartz grains in a fine-grained matrix may resemble mylonites. The quartz may show undulose extinction and resemble porphyroclasts in a mylonite (compare Fig. 10.2). However, in real mylonites quartz is the weaker mineral and tends to form the matrix rather then the porphyroclasts. An exeption to this are mylonitised ignimbrites or other volcanic rocks (e.g. Figs. 9.5.46 and 9.5.47; Passchier & Trouw 2005, their Figs. 3.9 and 3.10).