Sanukitoid

thumb|Sanukite is a black hard rock produced in Mt. Nijo on the boundary of Osaka and Nara prefectures

Sanukitoids are a variety of high-Mg granitoid found in convergent margin settings. The term "sanukitoid" was originally used to define a variety of Archean plutonic rock, but now also includes younger rocks with similar geochemical characteristics. They are called "sanukitoid" because of their similarity in bulk chemical composition to high-magnesium andesite from the Setouchi Peninsula of Japan, known as "sanukites" or "setouchites". Sanukite rocks are an andesite characterized by orthopyroxene as the mafic mineral, andesine as the plagioclase, and a glassy groundmass. Rocks formed by processes similar to those of sanukite may have compositions outside the sanukitoid field.