physical changes—two types\nin addition to changes in mineralogy, metamorphic rocks can also develop new…

physical changes—two types\nin addition to changes in mineralogy, metamorphic rocks can also develop new fabrics in response to pressure (fig. 6.4). there are two types of pressure - induced fabrics—lineation and foliation.\ntype 1\nlineation (french ligneage, line), is a linear fabric. example: stretched pebbles in metaconglomerate so as to be elongated (fig. 6.4a). the long axes of stretched pebbles collectively comprise a lineation.\ntype 2\nfoliation (french foillage, leaf), is a tabular fabric. there are two kinds of foliation: one (figs. 6.4b, c) is manifest in the parallel orientation of plate - like minerals (e.g., clays and micas), which imparts rock - cleavage (not to be confused with mineral - cleavage). this is called slaty cleavage in slate and schistosity in schist. both slates and schists develop from shale, but schists result from greater pressure. the hardness and smooth cleavage of slate make it ideal for roofing shingles, floor tile, chalkboards, and pool tables.\nthe other type of foliation (fig. 6.4d) is manifest in the segregation of light minerals and dark minerals into layers, imparting a banded appearance. this rock is called gneiss. gneiss does not exhibit rock - cleavage as do slate and schist.\nq6.4 imagine pebbles in a metaconglomerate that have been stretched (elongated) and flattened by pressure, so as to exhibit three axes of different lengths. do such strained pebbles exhibit lineation, foliation, or both?\nq6.5 examine the before - and - after fabrics (and captions) in figure 6.4b and explain how slaty cleavage can be distinguished from the fissile sheet - like breaking of shale. hint: notice the sedimented sand grains and the two captions.

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