Hi,

Did the paper get hung up? I will defend May 24th at 10:00 AM.

Mike



Michael P. Terry
Department of Geosciences
University of Massachusetts
Amherst MA 01003
Phone:  413 545 2286
Fax: 413  545 1200


-----Original Message-----
From:	Robert Tracy [SMTP:[log in to unmask]]
Sent:	Wednesday, April 26, 2000 2:46 PM
To:	[log in to unmask]
Subject:	Re: High potassium bearing mineral

 << File: ATT00000.html >> >
>Accordingly, let's forget my hypothetical "new mineral", K4Al3Si6O16(OH)5!
>But the reaction relationship among lithosite, muscovite, quartz and
>Kfeldspar is no less intriguing:
>
>K6Al4Si8O25.2H2O + KAl2AlSi3O10(OH)2 + 10 SiO2  =  7 KAlSi3O8 + 3 H2O 
>
>How commonly has lithosite been misidentified as "white mica" in high P/T
>chlorite-zone rocks that lack Kfeldspar?
>
>Dugald
>
>Dugald M Carmichael                    Phone/V-mail: 613-533-6182
>Dept of Geological Sciences and Geological Engineering
>Queen's University                              FAX: 613-533-6592
>Kingston  ON  K7L3N6             E-mail: [log in to unmask]


Dugald,

Your comments lead me to pose several parallel questions, one of them 
an old standby, and to muse about their implications:

1)  How commonly has non-porphyroblastic cordierite been 
misidentified as quartz in lower-P, moderate-T pelites?

2)  How commonly have margarite or pyrophyllite been misidentified as 
"white mica" (e.g., muscovite) in high-P amphibolite-facies pelites 
or low-T pelites, respectively?

3)  How commonly has hogbomite been misidentified as biotite in 
contact aureoles or pelite xenoliths?

These (and many similar questions) raise an additional philosophical 
question - how sure can we be normally (75%, 90%, 99%?), or SHOULD we 
be, that we have correctly identified all minerals present in any 
given thin section?  I'm sure each of us has a guess based on his/her 
degree of hubris regarding our petrographic abilities, but short of 
hitting every single grain with the probe beam (I have considered 
this in several cases and believe Dave Mohr may actually have done 
so) and at least accumulating and interpreting an EDS spectrum for 
each grain, it seems to me we always have to live with the 
possibility that something has been missed (maybe something 
important) because it masqueraded petrographically as a more 
"expected" or common mineral.  I regard myself as a reasonably good 
petrographer, but will readily admit that most of the IDs of more 
unusual minerals I have made have resulted from accident or 
serendipity and I sometimes wonder what I missed (not much sleep 
lost, however).  I remain in awe of the petrographic acumen of the 
old-timers who were able to do amazing feats in fine-grained rocks 
using only an optical microscope - a good example is Tilley's work on 
the ultra-fine-grained contact-metamorphic marbles/calc-silicates of 
Scotland and Ireland - but increasingly few of us have abilities 
approaching that level.

As we head into an era where technology actually allows us to 
characterize each and every grain in a thin section (in terms of 
identity, major and minor elements, trace elements and even isotopes) 
how strong is the justification to spend the considerable time (and 
NSF or NSERC money) required to do so?  Does our future lie in ever 
more detailed examination of fewer and fewer rocks or should we be 
looking with typical resolution at MORE rocks from a wider array of 
places?  I'd like to hear what our world-wide community of 
metamorphic geologists thinks about these issues.

Bob T.
-- 
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Dr. Robert J. Tracy
Professor of Geological Sciences
Virginia Tech
Blacksburg VA 24061-0420

540-231-5980
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