Hi Jeff and list >You are correct that the scale >should not be thought of as linear.
Ok ... But when it is not linear, there must be specific definitions for each subdivision ?. Best Lars ----- Original Message ----- From: "Jeff Grossman" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Thursday, March 13, 2003 8:31 PM Subject: Re: [meteorite-list] Re: Petrologic types and point values > No, it's simple. The decimals divide petrologic type 3 into ten finer > divisions. They are meant to convey a sense of relative metamorphic grade, > just as the original 3-4-5-6 numbers did. The reason this was done for > type 3 and not for 4-5-6 is that the differences between a low-type-3 (now > 3.0) and a high-type-3 (now 3.9) are as important as the differences > between a type 4 and a type 6. So it was decided that subdivision was > needed to make these distinctions (I was a coauthor on that original Nature > paper proposing this scheme back in 1980). You are correct that the scale > should not be thought of as linear. > > jeff > > At 02:18 PM 3/13/2003, E.L. Jones wrote: > >Hello Gents, List > > > >To my best recollection, the decimal value is not a scale from 3 to 4, > >such that 3.5 is "half way" would be between the two grades. It is an > >index for another characteristic peculiar to feldspathic minerals , I believe. > > > >The value after the decimal (e.g. 3."X", 3.5, 3.7 etc.) is a index of the > >degree to which some feldspar content fluoresces, indicating another, > >specific type of metamorphic process beyond the equilibration( > >comingling/co-melting) of all types of chondrites as they move from > >3-4-5-6 etc. I infer that the process is lost after stage 3 and may be > >insignificant(???) > > > >Perhaps someone else would offer the specifics as to who designed the > >index and what its significance is. We have discussed this before perhaps > >it is in the archives. > > > >Regards, > >Elton > > > >Lars Pedersen wrote: > > > >><snip>? > >>But what is the "tecknical" background for 3.2 - 3.8 ? > >>I would like to dig a litle bit deeper. > >> > >>Thanks > >>Lars > >> > >> > >> > >>>Hei Lars, > >>>Even finer grading, lowest value of 3.x means the chondrules > >>>are the most distinct, higher values that they become > >>>more 'blured'. But even 3.8 are quite distinct since > >>>it's 3, not 4,5,6 in the first place. > >>> > >>> > >>> > > > > > > > >______________________________________________ > >Meteorite-list mailing list > >[EMAIL PROTECTED] > >http://www.pairlist.net/mailman/listinfo/meteorite-list > > Dr. Jeffrey N. Grossman phone: (703) 648-6184 > US Geological Survey fax: (703) 648-6383 > 954 National Center > Reston, VA 20192, USA > > > > ______________________________________________ > Meteorite-list mailing list > [EMAIL PROTECTED] > http://www.pairlist.net/mailman/listinfo/meteorite-list ______________________________________________ Meteorite-list mailing list [EMAIL PROTECTED] http://www.pairlist.net/mailman/listinfo/meteorite-list
