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Description: This metamorphic rock is a highly weathered schist containing the metamorphic mineral staurolite (knobby crystals protruding slightly from the rock). Staurolite is mostly localized to the top-most area of this rock, reflecting the different elemental compositions of the sedimentary protoliths (parent/original rock) that were metamorphosed. For instance, a shale bed beside a sandstone bed will display very different mineralogy when metamorphosed since their bulk elemental compositions are very different. Staurolite is a useful metamorphic ‘index mineral’ that allows geologists to determine the approximate pressure-temperature conditions under which the rock was subjected during metamorphism.