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.
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