--- Michael Edison <[log in to unmask]> wrote:
> As for calcium carbonate and healing, I have heard
> it argued that the solubility of calcium carbonate
> is so low that the process of stalactite formation
> is more of a physical erosion and transportation by
> water of tiny limestone particles, rather than an
> actual dissolution of same.
>
> I'm not sure that's entirely correct. I suspect that
> even slight solubility can account for some of what
> we see in processes like formation of efflorescence.

Stalactite formation is, I always understood, driven
by the fact that all rainfall is slightly acidic, even
naturally.  This predisposes toward the dissolution of
calcium carbonate.

However, with the formation of efflorescence, and
particularly the hard crusty stuff when water leaches
through the joints, is probably driven by the solution
of lime-bearing material which is not calcium
carbonate.  I see the biggest problems with formation
of hard crusty efflorescence where water has been
migrating through paving beds ... which are invariably
formed out of a dry mix of cement and sand ... and
therefore has almost certainly not had enough water
for all of the Portland cement to properly hydrate ...
which I suspect means that there are still plenty of
soluble salts around to dissolve in the water and move
out into the open air to precipitate out in full view.

Cheers
david


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