Item talk:Q43004

Mindat Description

Granulite is a high-grade metamorphic rock in which the presence of feldspar and absence of primary muscovite are critical

Geoscience Ontology Description

Wimmenauer (1985) requires granulite to consist of at least 20 percent feldspar. Garnet is frequently present; some hornblende or biotite may be present. The rock has a granoblastic texture and gneissose to massive structure; grain size and fabric may be variable on a decimetric scale. Foliation is less well developed than in rock that would typically be called gneiss. The minerals present in a granulite vary depending on the protolith and the temperature and pressure conditions experienced during metamorphism. According to Fettes and Desmons (2007) the main calc-silicate minerals are calcic garnet, calcic plagioclase, calcic scapolite, diopside-hedenbergite, epidote group minerals, hydrogrossular, johannsenite, prehnite, pumpellyite, titanite, vesuvianite, wollastonite. Note that the shale and siltstone categories may apply to any of the mineralogically defined mudstone categories. Metamorphic rock of high metamorphic grade in which Fe-Mg silicate minerals are dominantly hydroxl-free; feldspar must be present, and muscovite is absent; rock contains less than 90 percent mafic minerals, less than 75 percent calcite and/or dolomite, less than 75 percent quartz, less than 50 percent iron-bearing minerals (hematite, magnetite, limonite-group, siderite, iron-sulfides), and less than 50 percent calc-silicate minerals.