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January 28, 1977

AIRMAIL

Dr. W. Compston
Research School of Earth Sciences, ANU
Canberra, A.C.T. 2600, Australia

Dear Bill,

I was interested to get your letter of January 20 and learn of your proposed work on possible variations of the isotopic composition of Ti in the Allende meteorite. However, your request for "a chunk of Allende, [[underlined]] at least [[/underlined]] several hundred grams [[underlined]] and with abundant inclusions" [[/underlined]] puts me on the spot; if there were such a chunk in our collection it would have been broken up long ago to satisfy the many requests we have received for such material. No chunk of Allende has abundant inclusions; some appear to have more than others, but selection of these is a chancy business at best. I recently spent several days working through our Allende material searching for inclusions for Ross Taylor to analyse; I found 18 in all, and sent ~100 mg samples of them to him. I suggest you examine these (if they have not already been crushed) and note any that might be suitable for your project; if you send me the sample numbers, I may have sufficient material remaining to send you some.

It appears to me that the only material suitable for your needs are the coarse-grained melilite-pyroxene-spinel-anorthite chondrules.  These usually contain 10-20% pyroxene, so to get the 10 mg pyroxene for your measurement, you will need at least 100 mg of starting material. I presume you plan to hand-pick the pyroxene; if contamination is not a problem, I would suggest heavy-liquid separation (the pyroxene is slightly denser than pure CH2I2, and the melilite and anorthite much less dense), and/or chemical separation (pyroxene is insoluble in HC1, melilite and anorthite dissolve readily). 

Rather than send you a chunk of Allende I think it might be preferable to try to find you 200 mg fragments of several melilite-pyroxene chondrules from among our material. However, if you feel that you would rather proceed as outlined in your letter, I will try to find you some suitable material. Would you be agreeable to accepting several chunks with a total weight of several hundred grams, rather than a single piece?

With best regards,

Sincerely yours,
Brian Mason 
Curator
Department of Mineral Sciences

BM/ks