Since Van Schmus and Wood (1967), the group/petrologic type designation has been entrenched (i.e., LL3.0, H4, L6), that it would be impossible to purge. So, calling Semarkona LL T3 just won't work -- no one would adopt it as a new convention. If we wanted to call Semarkona LL3.00 A2.8, that might be okay, but you would have to convince people first that a two-tier system is needed. It is probably best to exclude weathering and shock stage since we cannot designate every property in a classification (e.g., average olivine Fa content, cosmic-ray exposure age, oxygen-isotopic composition, chondrule size, etc.). A problem of course is that it may be difficult to disentangle thermal metamorphism from aqueous alteration, leaving a researcher baffled as to what to designate a particular rock. It would be better to leave out a classificatory parameter and to just guess and have the rock misclassified.
Alan Rubin Institute of Geophysics and Planetary Physics University of California 3845 Slichter Hall 603 Charles Young Dr. E Los Angeles, CA 90095-1567 office phone: 310-825-3202 fax: 310-206-3051 e-mail: aeru...@ucla.edu website: http://cosmochemists.igpp.ucla.edu/Rubin.html -----Original Message----- From: meteorite-list-boun...@meteoritecentral.com [mailto:meteorite-list-boun...@meteoritecentral.com] On Behalf Of Mark Bowling Sent: Saturday, April 12, 2014 8:13 AM To: Meteorite List Subject: Re: [meteorite-list] petrological type Would the following convention work? Letter designations would be used for each type of metamorphism. T for Thermal and A for aqueous. For a range of values, a dash could be used. So your example of Semarkona would end up as follows: Semarkona LL T3 A2.8-2.9. Using letter designations is already done for shock metamorphism and weathering grade. So when adding those, Semarkona would become (i'm guessing): Semarkona LL T3 A2.8-2.9 S? W0 It gets to be rather cumbersome, as you say, but if it were used, one could then quickly get an idea of the "geological" history of a particular specimen, just from the classification. Here is Dho 1073 as an example (and again I'm guessing on the values): Dho 1073 CV T3 A2 S2 W2-3 Capturing the order in which they occur could also be done (if you wanted to get that much information packed into a classification scheme). Something earlier would be placed first. If concurrent, they are linked with a slash. So the prior example, thermal metamorphism would have happened first. If aqueous alteration was first, then it would be designated as: Dho 1073 CV A2 T3 S2 W2-3 If A & T happened together, it would be: Dho 1073 CV T3/A2 S2 W2-3 But I'm not sure if that is practical - if the order is not always clear (or if effort to make a determination is rarely given), specifying order would be unreliable and inconsistent. Such information, if known, would be better communicated in the writeup. Next, if any of these types of metamorphism cannot or never occur in a particular class, you can leave out that letter. I would think it's safer to not assume it doesn't/cannot occur (simply because we don't have an example), and instead use a question mark in place of a number. e.g. Golden Mile H T4 A? S1 W1 (Congratulations Twink!). It's pretty tedious and intimidating, but with a little practice, people would soon be able to understand quite a bit more about a rock just by seeing the classification. Plus it could always be simplified, whereby a stone could be designated as an L3.0. And people would pretty much understand what that means or could imagine what it would look like. Or for those unconcerned, they could use everything as it now is, while scientists could adhere to the above convention in order to better communicate with each other. This is a interesting topic, thanks for kicking it off Francesco! Have fun! Mark ----- Original Message ----- From: Alan Rubin <aeru...@ucla.edu> To: 'Mark Bowling' <mina...@yahoo.com>; meteorite-list@meteoritecentral.com Cc: Sent: Friday, April 11, 2014 10:10 PM Subject: Re: [meteorite-list] petrological type Several people have informally suggested a two-tier system. It would work something like this. For example, on a metamorphic scale, Semarkona is type 3.00, but on an independent aqueous alteration scale it would be 2.8 or 2.9. Similarly, CR chondrites could all be 3.0 on a metamorphic scale, but range from 2.0 to 2.8 on an aqueous alteration scale. This is admittedly cumbersome, but it would be fairly useful. However, there are some carbonaceous chondrites that seem to have been altered and then metamorphosed; they would be hard to deal with. Also, if a rock is hydrothermally altered (i.e., subjected to metamorphic heating and aqueous alteration at the same time), that would also not be covered by such a scheme. Fitting complex rocks into classificatory straightjackets might obscure more than it reveals. Alan Alan Rubin Institute of Geophysics and Planetary Physics University of California 3845 Slichter Hall 603 Charles Young Dr. E Los Angeles, CA 90095-1567 office phone: 310-825-3202 fax: 310-206-3051 e-mail: aeru...@ucla.edu website: http://cosmochemists.igpp.ucla.edu/Rubin.html -----Original Message----- From: meteorite-list-boun...@meteoritecentral.com [mailto:meteorite-list-boun...@meteoritecentral.com] On Behalf Of Mark Bowling Sent: Friday, April 11, 2014 10:01 PM To: meteorite-list@meteoritecentral.com Subject: Re: [meteorite-list] petrological type Are there any better alternatives that could someday replace the current one, and do you have any references/links for them? Thanks, Mark ________________________________ From: Jeff Grossman <jngross...@gmail.com> To: meteorite-list@meteoritecentral.com Sent: Friday, April 11, 2014 5:22 PM Subject: Re: [meteorite-list] petrological type Answer: you can't. The classification scheme is lousy. Jeff On 4/11/2014 1:21 PM, Michael Mulgrew wrote: > Two sequences, one for aqueous alteration and one for thermal > metamorphism (http://www.meteoritemarket.com/PetTypeGroup.jpg). Makes > one wonder how we would classify a meteorite that is both thermally > and aqueously altered... > > > Michael in so. Cal. > IMCA 3963 > > On Fri, Apr 11, 2014 at 10:14 AM, Francesco Moser <coj...@tiscali.it> wrote: >> Hello, I have a question about chondrites' petrological type number assigned >> after the letters (like H, L, CM or CR ...). >> I have just read something in internet but I think I have misunderstood >> something. >> >> Are the numbers from 1 to 7 in sequence or there are two different >> sequences: 1 to 2 - 3 to 7 ?? >> 1 to 2 is for the aqueous alteration degree in carbonaceous chodrites (1 >> high degree, 2 low degree) >> 3 to 7 is for thermal metamorphism degree? >> >> >> Thanks a lot >> >> Ciao >> >> <x>x<x>x<x> >> Francesco >> ______________________________________________ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list ______________________________________________ Visit the Archives at http://www.meteorite-list-archives.com Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list