Dear GJ,

any idea if the material is a carbonate? if not  the material you found my
be oxalate, which is a common mineral found on paintings and monuments and
fungi. You can find a discussion of its origin on paintings in Del Monte et
al. (1987) Sci. Total Environment, 67, 17-39, in fungi (with some isotope
data as well, if I remember correctly) in Russ et al. 1996 (Quaternary
research, 46, 27-36)
We did a study of different oxalate occurrences, and found oxalates with
delta 13C of up to +33.7 permil PDB.

best regards
stefano


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Dr. Stefano Bernasconi
Geologisches Institut
ETH-Zentrum
CH-8092 Zuerich
Switzerland
Tel. ..41-1-632 3693
fax:  ..41-1-632 1080
e-mail: [log in to unmask]
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