Steve... Careful...alot of chalk is not calcium carbonate but calcium sulphate! John --oOOo----oOOo----oOOo----oOOo----oOOo----oOOo----oOOo----oOOo----oOOo- http://http.tamu.edu:8000/~jmd9261 jdavis at bio_tamu.edu jmd9261 at tam2000_tamu.edu ----------oOOo----oOOo-------------------------------------------------