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

On Jan 7, 11:37 am, Jo Schaper <jo345sch765a...@xxxxxxxxxxx> wrote:
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.

Yes, I don't think it's in keeping with recommended nomenclature to
call a formation with various carbonates a 'Dolomite' or 'Limestone'
unless they were named long ago. If it doesn't fizz when powdered, one
must ask whether it is magnesian limestone (with Mg > 15%), dolomite,
or mixtures including other carbonates. When the organic acidic
granules I'm fond of indicated a different carbonate was present, the
powder method graded nicely into simple wet-chemical tests to better
identify the carbonates. Here's a long quote that might interest you.
I've not read Logan, but you might find ideas for distinguishing
various carbonate facies in his writings.

'When Sir William Logan was carrying on the survey of the Laurentian
limestones of Canada, he received much help from what he called his "
limestone spear." This was a sharp-pointed bit of iron fixed to the
end of a pole or a walking-stick. He enlisted farmers and others in
his operations, instructed them in the use of the spear, and obtained
information which gave him a good general notion of the distribution
of the limestone. The spear was thrust down through the soil until it
struck the rock below. It was then pulled up, and the powder of stone
adhering to the iron point was tested with acid. If, after trying a
number of places all round, the observer uniformly obtained a brisk
effervescence when the acid drop fell on the point of his spear, he
inferred that the solid limestone existed below, and noted the fact on
his map accordingly.'

Geikie, A. 1882. Outlines of Field Geology, 3d ed. London: MacMillan,
p. 27-8.

Bruce

.

Relevant Pages

  • Re: Quartz Origins (Uh-Oh, Another Geology Post)
    ... 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 ... the term magnesian limestone to me is indistinguishable from secondary dolomite. ...
    (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. ... I've also picked out limestone exposures in putative ... call a formation with various carbonates a 'Dolomite' or 'Limestone' ...
    (sci.geo.geology)
  • Re: Quartz Origins (Uh-Oh, Another Geology Post)
    ... this requires practicing with various known carbonate ... powdered dolomite not fizzing in an appropriate acid. ... It is fairly easy to tell the limestones ...
    (sci.geo.geology)
  • Re: New Thread.
    ... Umm, incorrect, since most limestone has only a percentage of it's ... composition as calcium carbonate. ... "dolomite" it simply means they want a CaCO3 ... I call the stuff "Calcium Magnesium Carbonate", ...
    (soc.culture.scottish)
  • 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. ...
    (sci.geo.geology)