Re: inorganic limestone ???

On Mar 1, 9:56 pm, Jo Schaper <jospamnotschaper34@5socket78dot9net>
wrote:
Frank Palmer wrote:
Okay, all limestone is inorganic, what I mean is that I'm aware of
shellfish and other marine creatures making parts of their bodies from
calcium carbonate. When they die, this falls to teh sea bottom and,
ultimately, forms into limestone.

What I would like to know is whether there is any other mechanism
which can form limestlne. Is there a non-biological process?

Oh, goody, goody...Something I *know* something about! *|:-)

Actually, there are three primary forms of limestone: The fossiliferous
stuff you refer to above, crystalline limestone, which contains no
fossils, is nearly all calcite, and can be deposited by changes in
temperature, pressure, or water chemistry (fresh-saline mixing zones)
and micrite-- which is a fine grained, non-crystalline limestone which
basically forms from a mix of lime and silicate (clay) mud --the limy
mud under pressure limestone, where the calcite is basically the cement
holding the clay together.

I shan't bore you, but instead refer you to:

Donald Langmuir, Aqueous Environmental Geochemistry, Prentice-Hall,
1997, Ch. 6 p. 193-230.

And
William B. White, Geomorphology and Hydrology of Karst Terrains, Oxford
University Press, 1988, Ch.8, p. 247-258.

In short: if you've ever cleaned out a hot-water heater in an area with
hard water, or had the plumber saw through a pipe to find it clogged
with calcite, you believe in precipitation, through the mechanism of
temperature change laying down calcite.

In natural systems, the question gets a little stickier. Even though the
primary deposition of tufa, travertine, cave speleothems etc. is largely
an agitation/offgassing process, initial deposition, and deposition rate
can be greatly enhanced by microbial sized plants or critters, which
sometimes provide nucleation sites for the calcite/limestone to
preferentially precipitate. In the case of tufa, algae, moss, and other
vegetative living things change the gas makeup of the water via
respiration/transpiration, and may enhance the chemical process. Oolitic
limestone (being formed as we speak in the Bahamas), is another case
where the deposition is primarily chemical, but each oolite is
precipitated around some bit of stuff--usually organic in nature.

There have been experiments where a sterile marble substrate was placed
in water saturated with respect to calcite, and growth on that substrate
was slower than on the surrounding 'dirty' rock. Even your hot water
heater is liable to contain microscopic critters which influence the
deposition rate.

If you are interested in a good lay treatment of this
biogeomicrochemistry (gack! choke!) see the book "Dark Life" by Michael
Ray Taylor.

Limestone. It's cool stuff. And then when it is dolomitized, it is even
cooler. Everyone knows Bowen's reaction series for silicates. Well,
that's pretty straightforward if you're used to classifying limestones,
or tracing the sedimentary series from calcite crystals through
limestone, to low-mag, or hi-mag limestone, to dolostone, to dolomite,
to those beautiful curved pink crystals, and onto magnesium carbonate.

Thanks.

.

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