Abstract

The existing terminology for the textural classification of metamorphic rocks does not adequately take into account rocks that lack compositional layering or an abundance of platy or prismatic minerals. Whereas many workers consider compositional layering an essential characteristic of gneisses, others apply the name gneiss indiscriminately to almost any foliated metamorphic rock. The term schist is commonly misused for rocks containing less than the required 50% platy or prismatic grains displaying a preferred parallel orientation. To clarify this confusion and better constrain the existing terminology, it is suggested that the term foliate, introduced in the early 1900's, be reinstated to describe all foliated metamorphic rocks and be used specifically as a name for rocks that lack compositional layering or at least 50% platy or prismatic grains exhibiting a parallel orientation. Mineralogical, compositional, and (or) genetic modifiers may be applied to the term foliate, as they are to other textural rock names.

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