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

On Jan 9, 5:55 am, Jo Schaper <jo34schape...@xxxxxxxxxxxxxxx> wrote:
Bruce Bathurst wrote:
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.

The formation names are what they are, and around here they include the
lithology, unless they consist of known mixtures of the base rock. The
Bonne Terre, is the Bonne Terre Formation, because it is a mix, and
everyone recognizes it.

Sorry, I didn't.

I appear to have confused you somewhat, so I write this to clarify
myself. Joe's rock I shall address later.

Jo:
Originally, these all were called 1st, 2nd, etc magnesian limestones.
However, the term magnesian limestone to me is indistinguishable from
secondary dolomite. With one possible exception, none of the Missouri
dolomites are primary dolomites. No one locally uses magnesian limestone
any more, as that term is 100 years out of date.

(Primary dolomites are very rare, found precipitating from hypersaline
environments. Essentially all dolomites are grown during replacement.
Don't confuse a magnesian limestone with a dolostone.) Sorry, we've
become confused. I thought you were complaining that (old) formation
names ending in 'Limestone' and 'Dolomite' contained significant other
carbonates.

Jo:
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.

Though stratigraphy is far from my specialty, I assumed you were
taught (correctly) that you can use an actual rock to name a formation
only if there are no beds or facies with other rocks. However, one
commonly keeps old names that did. Hence my agreeing with you.

This post seem to be correcting this quote:

Bruce:
Deer, Howie, & Zussman still recommend Meigen's test to distinguish aragonite from >calcite, and Lemberg's test to distinguish calcite, magnesian limestone, and dolomite. >These are described in standard references.

Most tropical aragonites (used to) quickly change to calcites, which
can contain large quantities (up to 30 mol %) of Mg, Fe, Mn, &c. Those
calcites with greater than about 15% Mg are high-magnesian calcites,
never dolomites, because (thermodynamic) solvi separate the two: their
distinction is a natural one, not an arbitrary, artificial one.

The use of 'magnesian limestone' for 'magnesian calcite' was a typo
(sorry), but it still makes the sentence true. They differ in that
magnesian limestone can be a mixture of, for example, dolomitized
fossils and a calcite cement (which, BTW, paleontologists prefered
oxalic acid to hydrochloric to separate.), or a replacement dolostone
may be a facies (Joe should think 'face it presents') of an original
limestone.

It was to map the facies boundary that I remembered the 'iron spear'.
Mapping through soils has always interested me, and once in the 60s, I
accumulated data on the depths of the houses of Sierran burrowing
animals. :-)

Admittedly none of my places of education promoted using crystalline
acid, or had iron spears over their fireplace mantles. These are some
of the reasons I read 19th Century classics. That doesn't mean I
didn't read further. (For example, the term 'magnesian limestone' is
alive and well, and quartz still melts about 2000 degrees Celsius.
Unless in a eutectic mixture, the range of its melting temperature
varies with the composition of the rock.)

I'll answer Joe in a separate letter. The appearance of banding in his
rock confuses me, because the light minerals gave the appearance of
being cemented. However, I'll look again.

Hope this clarifies things. Some Canadian geologists may have better
insights into Logan's mapping techniques.

My best,


Bruce

.

Relevant Pages

  • 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 ...
    (sci.geo.geology)
  • Re: New Thread.
    ... I thought Dolomite and Limestone to be the same. ... The major components of a rock are primarily ... calcite than dolomite in a sedimentary rock (carbonates being the primary ...
    (soc.culture.scottish)
  • 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: 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 ... mine does not...your rock is ...
    (soc.culture.scottish)
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