ABSTRACT
The word pelite is derived from Greek, meaning clay-rock. The derivation is apt because pelitic rocks (shales etc.) are formed mostly from clays that are produced from the chemical weathering of feldspars, micas, and other minerals. Shales are the most abundant sedimentary rock type, so not surprisingly metamorphic rocks derived from them are also abundant. Although shales can themselves seem monotonous and nearly featureless, metamorphosed shales can differ strikingly from one another in appearance. They can range from extremely fine-grained slate, perhaps not so different in appearance from the original shales, to spectacular rocks bearing colorful, coarse crystals, complex textures, pegmatites, gleaming cleavage surfaces, and a host of other indicators of metamorphic history. Because Al-rich clays and quartz are commonly the dominant protolith minerals in shales, pelitic metamorphic rocks also tend to be dominated by quartz and aluminous minerals like muscovite, staurolite, the aluminosilicates, cordierite, and garnet. Pelitic rocks can host spectacular lineations, foliations, and folds at scales ranging from microscopic to kilometers across.
