Yes, the OsCal brand uses oyster shell sources. I never would let my customers choose it. Some calcium carbonate is manufactured in chemical plants, and supposedly that contamination (which also includes cadmium in addition to lead now BTW) is supposed to be not a worry. The best way to tell is to read the labels carefully. Oyster shell must be listed in the ingredients if present.

The citrate form is slightly better absorbed, and also good for patients with a history or worry about kidney stones. Citrate helps prevent the calcium oxalate type which about 80% are.

But yes, thanks for the reminder, Chemar!