Re: KRS - artificial weathering

From: zolota (zolota3_at_REMOVEshaw.ca)
Date: 09/17/04 

Date: Fri, 17 Sep 2004 05:56:49 GMT

"Eric Stevens" <eric.stevens@sum.co.nz> wrote in message
news:dbtik0hl6215lkksjiqsi0f3dvdjg4bgsl@4ax.com...
> On Wed, 15 Sep 2004 09:49:55 GMT, "zolota" <zolota3@REMOVEshaw.ca>
> wrote:
>
>>
>>"Martin Reboul" <martin.reboul@SPAMFUKvirgin.net> wrote in message
>>news:tdj1d.171$P02.102@newsfe3-gui.ntli.net...
>>>
>>BIG SNIP
>>
>>>>
>>>> Something to ponder is that micas are attacked by sulphuric acid.
>>>> Biotite,
>>>> the marker mineral used, is especially reactive, muscovite less so. A
>>>> fresh
>>>> surface with micas in it will show flakes protruding out of the matrix,
>>>> like
>>>> sultama rasins in a biscuit. Sulphuric will not attack the other
>>>> minerals
>>>> in a greywacke, so the result is to eat off the edges of the biotite
>>>> until
>>>> it is flush if given time. Less time and acid would convert the surface
>>>> of
>>>> the mica into vermiculite that has the softness of talc and would
>>>> readily
>>>> abrade in dirty water. Also, heating the surface in a fire to 800 deg C
>>>> will
>>>> cause it to calcine (oxidize). So, in 24 hours you can convert a fresh
>>>> surface into an aged one, mica-wise.
>>>>
>>>>
>>> http://www.altamet.com.au/Technical%20Papers%20and%20Articles/ALTA%20Copper/Over
>>> view%20of%20Gangue%20Mineralogy.pdf
>>>>
>>
>>>> http://www.geocities.com/mineralsgems/Identifyingmineralschemicalanalysis.htm
>>>>
>>
>>>> and in hydrochloric acid
>>>>
>>
>>>>
>>> http://technology.infomine.com/enviromine/ard/Acid-Base%20Accounting/ABAdiscussi
>>> on.htm
>>>>
>>>
>>> This is the sort of pertinent information, scientific method and
>>> analysis
>>> we
>>> need!
>>> Thanks...
>>> Cheers
>>> Martin
>>
>>Thanks. something that I note is that no one asked about how sulphuric
>>acid
>>could be used to age such a surface without damaging the calcite that is
>>present. Calcite (CaCO3) is extremely soluble and is the mineral of
>>limestone whose solubility results in caves from the action of simple
>>carbon
>>dioxide in the armosphere dissolved in water.
>>
>>Sulphuric acid immediately creates a layer of gypsum on the surface of the
>>calcite that protects it from further etching. This would result in a
>>calcite surface whose shape is fresh but whose chemistry is not. A forger
>>can get around that by starting with some hydrochloric acid that will
>>round
>>off the corners and age the surface in mechanical appearance before using
>>sulphuric acid to break down the mica. I'm not sure if a 19th century
>>forger
>>would know about gypsum on a calcite crystal, but he would want the stone
>>to
>>look aged.
>>
>>Conversely, a scan today that detected a gypsum surface IMHO cannot be
>>interpreted as either artificial or natural aging. Sulphate molecules are
>>abundant in soils and their presence is not anomanous. If there is pyrite
>>nearby (allegedly present in the KRS) then its to be expected.
>>
>>A second form of weathering is the spalling of entire crystals and chunks
>>of
>>rock, producing the pits we see on formerly smoothly polished stone. That
>>can be done by thermal cycling, a cycle consisting of time beside a hot
>>fire
>>followed by splashing on ice water, then letting it totally cool in an
>>winter night, then bringing it inside to the fire again. A few cycles
>>would
>>also tend to round off sharp edges on quartz and other silicate crystals
>>present. Thermal cycling would leave no chemical residue for later
>>inspection on most minerals.
>>
>>Themal cycling would however speed up the oxidation of pyrite which is
>>also
>>artificial aging. Pyrite in nature can oxidize in a few years so
>>converting
>>fresh faces is critical to a forgery. peroxide will also dissolve/convert
>>pyrite.
>>
>>Does anyone here see an error in my thinking, or a way that such
>>artificial
>>aging could be detected?
>
> To use your first example, a short time of exposure to reasonably
> concentrated Sulphuric acid may produce much the same surface results
> as a long time of exposure to dilute sulphuric acid (i.e. suitable
> natural sulphate soltions). You may be able to deal with the gypsum
> problems as you described but what about the subsurface reactions
> relying on a slow rate of permeation? The increased concentration of
> the acid on the surface will not make up fo the short time of
> exposure. The concentration gradient of SO4+ in the stone will be all
> wrong and so too will be the pattern of subsurface reaction products.
>

So far I have only addressed two minerals in detail. The first is the
biotite that has been mentioned most often for dating the KRS. The second is
the calcite that is also an acid soluble mineral. Biotite as far as I
remember only occurs in three geometries in a broken surface. Known as a
book, a mica grain is actually a stack of sheets that are strong in the two
dimensions but very weak in attraction between sheets. #1 orientation is to
be sticking out from the surface with it's roots in the rock. #2 is to
actually make up the surface, ie the rock split through a mica grain leaving
a mica surface. #3 geometry is that of the edge of the mica *** visible
where it plunges into the rock, the result of weathering of the rest of a
book in 1 or 2 above. Since a *** can peel off the book, the only
available comparison is to compare the books in a fresh surface with what
remains of them in the weathered surface. As I have observed them the books
sort of swell as they decompose, like a paper book that got wet. It is a
know fact that this process can be completed in short order (hours) using
strong acids. SO4 cannot penetrate the book to depth, think the curling
pages of a paperback in a fire vs a hard cover book. The reaction stops or
seriously slows down when condition #3 is reached. After a couple of water
washes an anomalous SO4 gradient in the mica would no longer exist if one
ever existed (SO4 cannot penetrate the book) but the surface would appear to
be ancient if the observer is familiar with biotite.

You must also remember that biotite burns at 800 deg C which can be reached
in a fireplace and even if not oxidation will occur at lower temperatures.
To put that in perspective, one minute at 200 deg C is theoretically equal
to 11 years at a constant temperature of 20 degrees C. Let's also consider
putting the KRS in a caultron and building a wood fire underneath it.
Oxidation would cease, but the speed of a dilute acid reaction would make
one day equal to about 10 Minnesota years at the same solution strength. Now
increase the strength by ---------?

As for all other minerals, name the ones that would also combine with
sulphate AND show a gradient through their surfaces.

It may be possible to detect some levels of chemical diffusion if you slice
the KRS through a letter although I'm not sure what could be seen. Do you
think that anyone will ever do this? Hint, don't hold you breath. The one
thing that comes to mind is that scan that shows when a rock was last heated
in a fire, now that would be interesting.

Z

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