[meteorite-list] Cosby's Creek, Tennessee

From: bernd.pauli at paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: 30 Mar 2007 18:59:17 UT
Message-ID: <DIIE.000000C600001945_at_paulinet.de>

Hi Robin and List,

Here is some interesting info from the Vagn Buchwald trilogy. Happy reading
and enjoy! For me, if I were you, the most interesting comment by Buchwald
would be this one: "It probably burst in the atmosphere and produced a limited
shower centered around Cosby's Creek" So, maybe there is still something out
there waiting for you to go for it!

Best wishes,

Bernd


BUCHWALD V.F. (1975) Handbook of Iron Meteorites, Volume 2, pp. 500-502, excerpts:

Cosby's Creek, Tennessee, U.S.A. / 35? 47' N, 83? 15' W; 450 m / Coarse octahedrite, Og.
Bandwidth 2.5?0.8 mm / Neumann bands / Group IAB-MG / 6.67% Ni / 0.53% Co / 0.29% P
91.5 ppm Ga, 431 ppm Ge, 2.9 ppm Ir

The greater part was forged, but about 100 kg fragments have survived in collections.

History: A fragment of a larger mass, found about 1837 near Cosby's Creek in Cocke County, was
described by Troost (1840) with an analysis. Further information was provided by Shepard (1842;
1847), and by Huntington (1888; 1894) who discussed the identity of a number of similar irons
(Sevier County, Greenbrier County, Jenny's Creek, Wilson County, Waldron's Ridge, Smithville
and Cosby's Creek), reportedly coming from different places in the Appalachian Mountains.
Several of Huntington's suite of irons certainly do not belong with Cosby's Creek, such as
Greenbrier County, Jenny's Creek, Waldron Ridge and Smithville. Black Mountain is probably a
transported fragment of Duel Hill (1873), since the detailed structures, the general locality
of find and the state of terrestrial corrosion are almost identical.

According to Shepard the greatest mass of 700-800 pounds weight (another less reliable estimate:
2,000 lbs) was found on an offset of an eminence about 30 m above the bed of Cosby's Creek.
It was an oblong, square block from which it was easy to detach fragments because of the violent,
 terrestrial corrosion that had taken place. The mass was "placed upon what is here called a log-heap,
 where after roasting for some time, it developed certain natural joints, of which advantage was taken
with cold chisels and spikes, for its separation into fragments. These were put into a mountain wagon,
and transported 30 or 40 miles" to Lary's forge in Sevier County and Peter Brown's forge in Greene
County. The greater part was wrought into "gun scalps" (in Tennessee the forged iron bar, before being
bored for a gun barrel, is called a "gun-scalp" - Huntington 1894), horseshoe nails and other articles
of common use, but some remnants of the mass fell into the hands of Dr. Troost. Another mass weighing
112 pounds, which was found in the immediate vicinity of the larger mass by a mountaineer, apparently
escaped the fate of the larger. It became known under the synonym Sevier County, was divided and went
through several hands (Troost, Shepard, Heuland), before it ended up in various collections, the largest
part presumably in the British Museum.
Many descriptions were given in the nineteenth century, of which, in addition to the above mentioned,
those of Reichenbach (1862a), Rose (1864a) and Smith (1876a) are noteworthy. Bergemann (1857)
and Cohen (1900b) presented the first reliable analyses, while Farrington (1915) reviewed the literature.

Description: Most specimens in collections are heavily corroded fragments with weights from a few grams
to a few kilograms. The original surface has lost its regmaglypts and atmospheric sculpturing due to
terrestrial weathering and is now covered with 1-3 mm thick adhering crusts. Most specimens appear to
be broken fragments; concave smooth impressions of now lost troilite-graphite nodules, 2-5 cm in size,
are often found in the fracture surfaces. Some specimens have a crust that indicates slight, artificial
reheating, since the color and morphology resemble scale on mill products. Such specimens are probably
surviving fragments of the larger mass that was heated in order to split it more easily.

Undamaged specimens show a coarse Widmanst?tten pattern with a bandwidth of 2.50?0.80 mm. The
thinner lamellae are invariably associated with cohenite-rich patches. In the cohenite-poor regions grain
growth has often wiped out the Widmanst?tten array and created almost equiaxial ferrite grains 3-20 mm
in diameter. Neuman bands are common.
 
Cohenite is the dominant mineral in most sections. It occurs typically as 3 x 0.5 mm oblong, rounded,
monocrystalline fingers and is occasionally clustered sufficiently to create rosette-like aggregates. Graphite
is common, probably always associated with troilite. Smaller graphite and troilite nodules are frequently
met with. Some appear to have been parallel, elongated cones of finger size that were easily detached
from the matrix. Daubreelite frequently occupies 5-10% of the troilite nodules.

Schreibersite is present as 10 x 1 mm skeleton crystals with cohenite rim zones. It further occurs as
grain boundary precipitates and as inclusions in cohenite. Phosphides are numerous as rhabdites.
Corrosion penetrates deep into the interior everywhere. Cosby's Creek is a typical inclusion-rich,
coarse octahedrite which is closely related to such irons as Seel?sgen, Duel Hill (1873), Cranbourne
and Gladstone. It probably burst in the atmosphere and produced a limited shower centered around
Cosby's Creek; specimens from this region were later recovered and described under the names:
Cosby's Creek, Sevier County and Wilson County.
Received on Fri 30 Mar 2007 02:59:17 PM PDT