Re: Daryl Krupa: Geology Question (KRS related)


"Daryl Krupa" <icycalmca@xxxxxxxxx> wrote in message
news:1138600323.430523.90870@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Steve Marcus wrote:
> <snip>
>> What I've learned, so far, about
>> the geology of the dating method employed
>> is that a weathering comparison was used to date the inscription
>> by comparing the KRS (which is
>> greywacke, a meta-sedimentary rock
>
> Steve:
> Just a point of clarification:
> graywacke (American spelling) is a sedimentary rock;
> metagraywacke is a metamorphic rock,
> which could be called meta-sedimentary.

Which is why I asked you for help. I couldn't tell whether the name
metagraywacke implied that the rock was sedimentary graywacke produced by
metamorphism, as slate is produced from shale.

> The KRS is best described as metagraywacke,
> in that it is graywacke that shows signs of
> having undergone metamorphosis
> (i.e., changes resulting from heating, pressing,
> and crystal growth and substitution, etc.).
> What does Wolter call it?

Metagraywacke.
>
>> bearing these micas: biotite, chlorite and muscovite)
>
> Chlorite is a flat *** silicate, like the micas,
> but it is not generally called a mica, though some would see it as
> related. From:
>
> http://www.eos.ubc.ca/personal/groat/claymanual.htm

I was working from this site, which gives "the most common" micas, and does
not list chlorite (but, of course, does not exclude chlorite as a member of
the mica grouping):

http://www.galleries.com/minerals/silicate/micas.htm

lass.htm#phyllo
>
> See also this description of the metamorphic
> origins of mica and chlorite:
>
> http://csmres.jmu.edu/geollab/Fichter/MetaRx/Metatexture.html
>
> Does Wolter say that chlorite is a type of mica?

Nielsen and Wolter's book, at page 34, discusses the mineralogy of the KRS
and states: "The elongated grains exhibit a preferred orientation that is
sub-parallel (nearly parallel) with the foliation composed of various mica
minerals (muscovite, chlorite and biotite) that comprise the matrix."

>
>> with three slate (a metamorphic rock) tombstones
>> from Augusta Maine
>> that were selected from a much larger number of tombstones
>> because the mica grain size in samples of those three tombstones
>> was comparable to the grain size of the KRS micas.
>> The authors only discuss biotite,
>> leading me to believe that the tombstones
>> did not have the other KRS micas.
>
> I wouldn't go that far. Absent a detailed description
> of the Augusta tombstones, we don't know that.
>
> Did Wolter say which formation the tombstone slate
> was quarried from?

Not that I've been able to see in the material that I've read so far. (I've
reached the end of the "tombstone comparison" material, but that doesn't
mean that more info re the tombstones won't crop up later in the book.) The
tombstones were from Hallowell Cemetary in Hallowell, ME.

Another tidbit: Nielsen/Wolter include a photo of lichens from one of the
tombstones (although it isn't stated whether it is from one of the three
tombstones from which samples were used to date the KRS). They state that
acid produced by these lichens would "accelerate the weathering rate of
biotite mica." (page 44, and Fig. 51 on page 46). No comment is made
regarding the possibility that given the similar climates of Augusta, ME
(evidently as close as to Hallowell, ME as they could gather data for) and
Kensington, whether it would have been likely that lichen would have grown
on the KRS (obviously any such material would have been removed in the
various cleanings that the stone received subsequent to its discovery).

>
> Yet the specific type of biotite was not given.
> I am not a petrology or mineralogy wizard, but
> I have seen descriptions of a single rock type
> with four phases of biotite, with different chemical
> makeup in each.
> The longer a rock is metamorphosed,
> the more the biotite that it contains changes;
> e.g., garnet can grow at the expense of biotite.
> I have also seen analyses of biotite weathering that distinguished
> between different types.
> This might be a case of comparing apples and
> oranges, WRT weathering characteristics of biotite.

>
>> The tentative dating for the KRS is
>> "older than 200 years" because
>> all of the mica minerals on
>> the "man-made surfaces" of the KRS
>> have weathered away
>> (it's not present in either the inscription or
>> the surfaces bearing the inscription),
>> while the biotite on the tombstones
>> (average age 194 + or - 5 years)
>
> Hmmm? I had thought that that was
> about the age of the oldest tombstone sampled.

"The average age of weathering of the three samples was 194 years, plus or
minus 5 years." The three sample tombstones had "death dates" of 1806, 1805
and 1815, yielding 197 years, 198 years, and 188 years of weathering in
2003.

>
>> is still present,
>> although it is severly weathered.
>
> If the weathering characteristics of the biotites
> in the Augusta tombstones and the KRS were similar,
> then that 200-year-plus age estimate might be
> a fair assumption.
> But it is as yet only an assumption, as
> the congruency of the two materials' weathering
> characteristics has not been proven.

Or, at least, haven't been stated by Nielsen/Wolter. I figured as much;
quite possibly, an apples/bananas comparison, all tricked out with some "8 x
10 color glossy photos", to borrow a nicely turned phrase from Arlo Guthrie.

>
>> It is noted that the tombstones are from
>> a geographical area stated in the text to
>> average 17 inches of rain per year more than
>> falls in Kensington (although tabular data
>> in the book states that the average is
>> 17 inches of *precipitation*,
>
> A minor flaw, perhaps resulting from
> an assumption that precipitation in Maine
> is mainly plain rain.

You would have thought that; I certainly did, until the authors noted that
they hadn't obtained any below ground samples from the tombstones because
the ground was frozen and covered in a foot of snow.

>
>> and although it is stated that both above and
>> below grade samples should have been compared,
>> only above-grade samples were collected from
>> the tombstones because the ground was frozen
>> and covered with a foot of snow.
>
> If we knew the burial history of the KRS, and
> how long any one side had buried, under what
> conditions, and for what amount of time, that
> might be a significant problem.
> But we don't, so I am content to limit the
> discussion to sub-aerial weathering (i.e.,
> that which comes about during exposure to weather).
>
>> Leaving aside the issue of differences in
>> average temperatures between Augusta ME and
>> Kensington, MN, as well as acid rain issues,
>> I'm wondering whether the comparison made by
>> the authors is geologically sound in the
>> sense of comparing apples to apples.
>> I don't know enough geology to know whether
>> the fact that the two rocks are of different
>> types, and the micas on the two different types
>> of rocks also being different different
>> (the rocks are reported as having only biotite
>> in common) amounts to comparing apples to bananas.
>
> I would be surprised to find that the only common
> mica between the KRS and the Augusta tombstone slate
> was biotite.
> A mention of the tombstones' parent formation
> would have been useful in that regard, or even
> the location of the quarry or quarries that
> supplied the cemetary.
>
> From an ancient tome on American slate quarrying,
> WRT Maine slate:
>
> 1906
> Slate Deposits and Slate Industry of the United States
>
> http://www.cagenweb.com/quarries/states/me-slate_1906.html
>
> "
> The constituents of this slate, arranged in
> the order of their decreasing abundance,
> appear to be muscovite (sericite), quartz,
> chlorite, biotite, pyrite, carbonaceous or
> graphitic matter, magnetite, rutile, and apatite.
> "
>
> Two types of mica there,
> the most important constituent of the rock (i.e.,
> the matrix that the other minerals occur within)
> being
> the mica known as muscovite.
>
> Similarly from 1914:
> Excerpts From
> Slate in The United States
>
> http://www.cagenweb.com/quarries/states/me-slate_1914.html
>
> That Maine slate seems to be made mainly of
> another type of mica than biotite seems
> to have been known for a century. Or more.
>
>> Any light you could shed on these points
>> would be appreciated.
>
> Hoping that this has been a start on answering,
> Daryl Krupa
>

Daryl, your time and your expertise are greatly appreciated. I'm trying to
approach the Nielsen/Wolter book objectively, looking for evidence that
solidly supports the logic of the authors and their conclusion. So far,
through about 60 pages, I haven't found a great deal of solid logic. Your
input seems to be that their "tombstone evidence" may be nothing more than
suggestive, but inconclusive.

Steve
--
The above posting is neither a legal opinion nor legal advice,
because we do not have an attorney-client relationship, and
should not be construed as either. This posting does not
represent the opinion of my employer, but is merely my personal
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