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Fossil Meteorites and Dangerous Females

Hello Rob, hello List!

Rob wrote:

> I'm not so sure Bernd...my wife has PLENTY to say when she sees my
> monthly Visa card statement for meteorite purchases and is best
> avoided until the dust settles. The "it's a good investment" excuse
> doesn't seem to work anymore.

Thanks, Rob. Now I know why my study room is so dusty, although I
constantly try to keep it free from dust. It just doesn't settle.

Rob also wrote:

> I'm not sure if this topic has been discussed before I joined the list
> but I came across a paragraph in an old book recently that seemed
> strange to me. It refers to the lack of meteorites found in ancient
> coal deposits.....I've scanned the text and attached it as an image.
> This is a fairly old book on meteorites and may well be completely out
> of date now, but maybe worthy of comment.....has anyone got any
> thoughts on this?

Rob, the article I mentioned in my Sat, 2 May 1998 14:42 reply to
Martin's contribution contains further interesting information with
regard to that subject =>

SICREE A.A. et al. (1997) Potential for preservation and recovery of
fossil iron meteorites from coal, trona,limestone and other sedimentary
rocks (Meteoritics 32-4, 1997, A121):

An iron meteorite falling into a coal swamp will develop a rind of
pyrite, siderite, or rust, which inhibits alteration of the interior of
the meteorite. After coalification, an iron meteorite encased in coal
will be preserved from further corrosion by the reduced state of the
coal, particularly in a coal seam with a methane-dominated vapor phase.
The discovery of native Fe in coal indicates that iron meteorites could
survive for millions of years in coal seams. Native Fe has been reported
in a Cretaceous coal from the Dutch Creek Mine, Pitkin County, Colorado,
where it occurs at the coal/coke interface adjacent to an intruding
felsic porphyry dike [4].
Other sedimentary environments that may have been conducive to
paleometeorite preservation include those in which trona, limestone,
sandstone, shale, gypsum, secondary kaolin, or salt were deposited.
Trona, a sodium carbonate mineral, is particularly favorable to the
preservation of metallic Fe, because of the relatively high pH and
strongly reduced state of groundwater in contact with the trona beds.
Estimates of the present-day flux of meteorites range from 100 to 1000
metric tons of meteorites per day for the whole of the Earth's surface
[5], about 1% of which is recoverable or macrometeorites, giving an
average macrometeorite flux of 1.8 x 10^ -7g/m^2 yr. About 5% of these
meteorites are strongly magnetic (i.e., iron, or stony-iron meteorites).
If coal accumulated at the rate of 0.1 mm/yr, then every million short
tons of coal should yield about 300 g of magnetic macrometeorites. A
large Western U.S. coal operation such as the Black Thunder Mine in
Wright, Wyoming, which mines more than 36 million tons of coal per year,
could yield about 10,000 g of magnetic macrometeorites per year. Similar
theoretical yield estimates have been made for other sedimentary rocks.
By examining materials captured by existing large electromagnets (used
to remove "tramp" Fe, such as drill bits, from the mineral stream)
suspended over conveyor belts at coal mines, it should prove possible to
recover fossil iron meteorites from the coal. Efforts to recover fossil
iron meteorites by this method are underway at coal mines in
Pennsylvania, Wyoming, and Montana, and at trona mines in the Green
River Basin of southwest Wyoming. This recovery method potentially can
be applied to other sedimentary rocks such as limestone and secondary
kaolin, the mines of which also often employ tramp metal electromagnets.

References:

[1] La Paz L.(1953) Meteoritics 1, 109-113.
[2] Thorslund P. and Wickman F.E. (1981) Nature 289, 285-286.
[3] Nyström J.O. et al. (1989) Nature 336, 572-574.
[4] Thorpe A.N. et al. (1997) in preparation.
[5] Parkin D.W. and Tiles D. (1968) Science 159, 936-946.

The author's (email) address is:
A.A. Sicree, Earth and Mineral Sciences Museum, Pennsylvania State
University, University Park PA 16802, USA (sicree@geosc.psu.edu).