0100,0100,0100Hi William: You can make life much easier if you first make 2 mirror-immage slabs, one is processed as the other you keep for microsampling under binocular microscope. In the thin section, you check the preservation of fibrous structure of crystals under polarizing microscope and the luminescence that they exhibit under luminoscope as well. You might recognize, under CL, alternate dull (summer) and bright (winter) layers due to changes in growth rate during seasons which is relative to the rate of incorporation of Mn that mainly causes bright red luminescence. The bright CL may also reflect alteration due to incorporation of Mn during diagenesis. Therefore, you may take a fraction from each layer and check it out under SEM to see the ultra structure and this is the most powerfull tool that will help you indentify the altered parts because you can see clearly the damage in the crystal structure caused by dissolution. In a later stage, you may run major and trace element analysis to confirm your results from petrographic criteria and to reveal any hiden alteration you could not recognize. The following references will help you a lot. Barbin, V. and Gaspard, D., 1995, Cathodoluminescence of recent articulate brachiopod shells: Implications for growth stages and diagenesis evaluation: Geobios, M.S., v. 18, p. 39-45. Azmy, K.; Veizer, J.; Bassett, M. and Copper, P., 1998. OXYGEN AND CARBON ISOTOPIC COMPOSITION OF SILURIAN BRACHIOPODS: IMPLICATIONS FOR COEVAL SEAWATER AND GLACIATIONS. GSA Bull., 110: 1499-1512. ---------------------------------------------------- Karem Azmy, PhD. Research Associate Department of Earth Sciences University of Ottawa 365 Nicholas St., Box 450, Stn. A Ottawa, Ontario, K1N 6N5, Canada Tel. (613) 562 5773 Fax. (613) 562 5192 e-mail [log in to unmask], [log in to unmask] http://www.science.uottawa.ca/users/azmy/ ----------------------------------------------------