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hi, recently Rolf Schmid, as a member of this subcommission, presented a poster about this topic. you can find him at the eth in zürich and the proposal for the nomenclature of metam. rocks at: www.bgs.ac.uk/scmr hope that helps ... robert ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Dr. Robert Schmid Institut für Geowissenschaften der Universität Potsdam Mineralogie-Petrologie Postfach 601553 14415 Potsdam Germany fon +49/331/977 2910 fax +49/331/977 5060 http://www.uni-potsdam.de/u/Geowissenschaft/Personal/personal.html ----- Original Message ----- From: Jean-Paul Liégeois <[log in to unmask]> To: <[log in to unmask]> Sent: Wednesday, November 07, 2001 12:18 PM Subject: Metam Rocks Nomenclature > Dear All, > > Jürgen wrote: > "There are always borderline cases where standard nomenclature may be > unsatisfactory. However, metamorphic rock nomenclature has the advantage > that it can cater for a lot of variety, and if one wants to be precise, one > can use as many qualifyers as necessary. It really depends on what one > intends to communicate to others." > > Then there is a standard nomenclature for metamorphic rock. Is it published > somewhere? As John Clemens already said, the IUGS subcommission on > metamorphic rocks nomenclature has not given yet its recommendations. In the > field, when dealing with metamorphic rocks and several geologists, the first > day generally consists in discussions about nomenclature to be able to > communicate. Even for words as "gneiss" or "micaschist" this is no agreement > (is gneiss indeed a purely textural term? what about the mylonitic > texture?). Working mainly in magmatic rocks where nomenclature problem is > mostly (not entirely) solved, I can see the softening in exchanges that this > gives. To answer to the magmatic nomenclature of Christian Nicollet, it is > indeed easy to give him the reference of the IUGS recommendation. Example: > an andesite is an intermediate volcanic rock usually porphyritic defined > first by mode (pl+px+hb +/-bi) and if not available by its SiO2 (57-63%) and > Na2O+K2O (max 6-7%) contents; this is a good example of the unambiguity of > the recommended classification. There is no relation made to the C-A or Alk > series (can be debated) but only to alkali content (could be debated if the > rock is altered, but at a lower level). > > I would then be grateful to know what this standard nomenclature for > metamorphic rock consists in. > > Have a nice day, > > Jean-Paul Liegeois > Head of Section, Isotope Geology > Africa Museum > B-3080 Tervuren, Belgium > Tel & Fax: +32 (0)2 6502252 > e-mail: [log in to unmask] >