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.
example
nebulite
note
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.
Fettes and Desmons (2007). See also Wimmenauer (1985), Winkler (1979) (D.R. Bowes
(1989), The Encyclopedia of Igneous and Metamorphic Petrology; Van Nostrand Reinhold
ISBN: 0-442-20623-2 ; wikipedia, http://en.wikipedia.org/wiki/Granulite accessed 5/30/09
