Re: Quartz Origins (Uh-Oh, Another Geology Post)


Jo Schaper a écrit dans le message ...
Bruce Bathurst wrote:
On Jan 6, 12:36 pm, Jo Schaper <jo34schape...@xxxxxxxxxxxxxxx> wrote:

None of the dolomite in Missouri (unless it is actually pink crystals)
is made properly, but I already know that, so I use other ways to
determine what carbonate I'm dealing with. *|:-)

Jo,

The oxalic acid crystals I used may occasionally have been citric acid
crystals - whichever was available at the time. Truly, I never carried
a plastic bottle of dilute hydrochloric acid on my belt, which always
seemed excessive.

As I noted somewhere else in the thread, I just carry a old OTC nasal
spray bottle with HCL clearly marked on it, I double bag it in ziplocks,
and it's in the pack, not on my belt. Never had an issue with it, since
that tiny squeeze spray hole is going to drip at best, even if the screw
on cap came off.

However, this requires practicing with various known carbonate
minerals before leaving for the field. You alluded once before to
powdered dolomite not fizzing in an appropriate acid. This I've never
encountered nor heard of; and it is important to geologists. I have no
explanation, other than it's being a different carbonate. If it didn't
fizz when powdered, how did you identify it as dolomite?

Most of my field work is done in Paleozoic (Cambrian-Mississippian,
occasionally Pennsylvanian) carbonates which are an
insane mix of of limestones, secondary dolostones, mudstones and thin
crumbly shales. The sandstones are pretty discrete; but the other three
sometimes interlayered and gradational. For the most part, the rock
units around here are named as Potosi Dolomite, St. Louis Limestone,
etc., so you would think knowing what unit it is in would be diagnostic,
but because the dolostones are of the replacement variety, actual
lithology varies quite widely. It is fairly easy to tell the limestones
from the dolomites by texture; once you get the sparry limestones out of
the mix, most of the limestones (grading into mudstone) are powdery, and
rather soft; the dolostones are gritty, compact and generally harder.
What confuses things even more are those incompletely dolomitized; it's
not that unusual to have fossils retained in the dolomite-- i.e. the
rock will not fizz, it's not shaley or muddy, but is carbonate and has
fossils in it. I've also picked out limestone exposures in putative
dolomites-- the book and the map says it should be dolomite, but it
fizzes like crazy. What prompts me to test such rock? Its texture and
eyeball muddiness.

I'm sure this method is non-scientific, and I don't expect it to work in
an unfamiliar area, so I'm not advocating it. But that's what I like
about geology-- every time you put information in little boxes, some of
it thumbs its nose at you and does the Nah-Nah-Nahnahnah! dance.

Standard for geologist worldwide is a 10% solution of HCL. A 1 molar
concentration which is sometimes used in soil science will generally not
react with dolomite. Even with a 10% solution the dolomite must be scratched
or powdered. Household vinegar used drop wise on limestone will not work (as
a rule) it must soak the sample. Just to make sure I tried using fresh lemon
juice on a almost pure limestone sample with no visible results. I would be
curious to know where in the literature is the use of oxalic acid crystals
recommended.
Here are some links that may be of use.
http://www.usbr.gov/pmts/geology/geolman/chap11.pdf
http://geographyplanning.buffalostate.edu/MSG%201998/2_Tang.pdf
http://serc.carleton.edu/files/NAGTWorkshops/sedimentary/activities/Greer_We
atherLabs.pdf
http://eesc.columbia.edu/courses/v1010/

Scientific discussion: Upon reaction with 10% hydrochloric acid, ...
Geologists use this behavioral difference as a field test to discriminate
between ... http://www.mii.org/pdfs/An_Acidic_Reaction.pdf

Someone reminded me that in the USA often the muriatic acid is sold as 22
degree baumé . This is 36% (11.64) molar . To get 10% (2.87M) add 258 ml of
the 36% acid to distilled water then dilute to 1000ml. If you have Chemical
company concentrated HCl that will be 12 molar. For a 3 molar concentration
(close enough for field work) just dilute by a factor of 4 or 250 ml in
distilled water then diluted to 1000ml.

JL




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Relevant Pages

  • Re: Quartz Origins (Uh-Oh, Another Geology Post)
    ... crystals - whichever was available at the time. ... powdered dolomite not fizzing in an appropriate acid. ... other than it's being a different carbonate. ...
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  • Re: Quartz Origins (Uh-Oh, Another Geology Post)
    ... The oxalic acid crystals I used may occasionally have been citric acid ... powdered dolomite not fizzing in an appropriate acid. ... other than it's being a different carbonate. ... I've also picked out limestone exposures in putative ...
    (sci.geo.geology)
  • Re: Quartz Origins (Uh-Oh, Another Geology Post)
    ... The oxalic acid crystals I used may occasionally have been citric acid ... powdered dolomite not fizzing in an appropriate acid. ... other than it's being a different carbonate. ... I've also picked out limestone exposures in putative ...
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