[Rockhounds] Pennsylvania fern fossils

[Earl R. Verbeek]

OK, I'll give it a shot.  The thermal maturation process that leads from
peat through lignite and bituminous coal to anthracite occurs at
temperatures and depths below those responsible for most of the metamorphic
rocks with which we are most familiar.  If you go to the anthracite coal
basins of Pennsylvania you'll find the strata deformed into wonderful
folds, but in those folds you'll see sandstone and siltstone and shale, not
slates or schists or gneisses.  The metamorphic grade is just too low for
those rocks.  You're correct that the St. Clair host rock is better termed
"shale" than "slate" because it splits along bedding, not cleavage, which
is largely (wholly?) absent.

Bear in mind that different rock type show obvious effects of metamorphism
at different temperatures and pressures.  Anthracite coal is described in
some texts as a metamorphic rock, in part because nearly all of its
original constituents are now unrecognizable as such, but the degree of
metamorphism required to change bituminous coal to anthracite is well below
that necessary to change other rock types to their common metamorphic
equivalents.  Other texts describe anthracite as a sedimentary rock, in
keeping with its association with other rocks that we still recognize as
shale and sandstone.

         Cheers-   Earl Verbeek



On Mon, 03 Nov 2008 19:24:42 -0500,  wrote:
> 
>  I've been reading about St. Clair material. People keep calling the
> matrix "slate". My specimens from there frequently are very detailed and
> not at all distorted as they might be if there was? more than a little?
> slate producing metamorphism. Also a thought that slate splits along
> planes perpendicular to the pressure, not along sedimentary layers
> containing the fern fossils. I also was told that this was a worked out
> anthracite location. How do you get shale type fossils and matrix next to
> an anthracite location.? Somebody set me straight. smkell
> 
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> 
> -----Original Message-----
> From: John Junkroski <jpjunk at mc.net>
> To: Rockhounds at drizzle.com: A mailing list for rock and gem collectors
> <rockhounds at lists.drizzle.com>
> Sent: Mon, 3 Nov 2008 2:12 pm
> Subject: Re: [Rockhounds] Pennsylvania fern fossils
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Hi Larry,?
> ?
> 
> I'd be very interested in those fossils.?
> 
> I have some 1 1/2 inch pyrite cubes from Spain to trade and some
> fluorescents from Ontario, Kentucky and California.?
> 
> Might be able to find some U.P. Michigan native copper...?
> ?
> 
> John?
> ?
> 
> 
> On Nov 3, 2008, at 10:11 AM, Lawrence Rush wrote:?
> ?
> 
>>?
> 
>>?
> 
>> I'm still digging through boxes of old material. Today the find is > of
> 3 large plates of fern fossils from St.Clair, Pennsylvania > (about 8X12"
> in size). I dug these some 35 years ago, when access > was still
possible.
> If any fossil collectors would like to trade > for these (for mineral
> specimens, please), give me a shout, and I > will send photos.?
> 
>>?
> 
>> Good Collecting........Larry?
> 
>>?
> 
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