Wikipedia states:
"Tufa is the name for an unusual geological form of calcite rock.
"Tufa is a rough, thick, rock-like calcium carbonate deposit that
forms by precipitation from bodies of water with a high dissolved
calcium content. Tufa is not to be confused with tuff which is
volcanic."
I know of no igneous rock here; everything is sedimentary. But I
guess it could be tufa.
On Nov 11, 2007, at 7:09 PM, <eureka AT hctc.net> <eureka AT hctc.net> wrote: