1.4 Two Names for Every Rock

Geologists have coined many names for metamorphic rocks. As with igneous rocks, in many cases more than one name was defined that could be used for the same rock type. To resolve conflicts and systematize the naming of metamorphic rocks, the International Union of Geological Sciences (IUGS) created a Subcommission on the Systematics of Metamorphic Rocks (SCMR). The recommendations of the SCMR can be found in a book and glossary (Metamorphic Rocks: A Classification and Glossary of Terms) and are summarized in a paper "How to Name a Metamorphic Rock" by Schmid and others (2007) available online.

In their recommendations, the SCMR compromised on a systematic classification that combines mineral names with structural terms (schist, gneiss, and granofels) that can be used for any metamorphic rock. However, the SCMR also retained specialized names based on particular rock types (e.g. quartzite, marble, slate), on types of metamorphism (e.g. mylonite, skarn), or on a known protolith (e.g. meta-conglomerate, metabasalt). To any of these names, the SCMR recommends adding mineralogical prefixes to the name, listing the major mineral constituents (>5%) in order of increasing modal abundance in the rock.

To name your own metamorphic rock by following the IUGS instructions, click here:

To see examples of metamorphic rocks in the Rock Library, click here:

If you want to try your etymological skills with some metamorphic rock names, click here: