Compressing a piece of paper would cause the flat dimensions to orient themselves perpendicular to the direction of compression. Likewise, when a metamor-phic rock is compressed or stressed, the platy minerals, such as chlorite and micas, orient themselves so that their long dimensions are perpendicular to the maximum compressive stress. The planar fabric that results from this process is known as a foliation.
slaty cleavage is a specific type of foliation in which the parallel arrangement of microscopic platy minerals causes the rock to break in parallel platelike planes. schistosity forms at higher metamorphic grades and is a foliation defined by a wavy or distorted plane containing large, visible, oriented minerals such as quartz, mica, and feldspar.
As rocks are progressively heated and subject to more pressure during metamorphism, different mineral assemblages are stable. Even though the rock may retain a stable overall composition, the minerals will become progressively recrystallized and the min eral assemblages (or parageneses) will change under different P-T conditions.
Continue reading here: Kinds Of metamorphic ROCKS
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