[meteorite-list] Sahara Sand and Michigan Dirt

From: Keith <littlejo_at_meteoritecentral.com>
Date: Thu Apr 22 09:52:18 2004
Message-ID: <Pine.SOL.4.33.0208191953070.10491-100000_at_katie.vnet.net>

In the thread [meteorite-list] Sahara Sand and
Michigan Dirt and on Thu, 1 Aug 2002 19:55:53 -0800,
Jeanne wrote:
>I will eagerly be awaiting any further thoughts
>you have on this! I wish I could take a picture
>of them.

...text deleted...

Mark Fox wrote:
>>I believe I have a clue to what you are describing.
>>On our farm I have often seen thin layers of what
>>appear to be dark grey to black particles in wash
>>outs. They are very minute to be sure. However,
>>a magnet readily attracts them as if they were metal
>>filings. If they were magnetite, wouldn't one expect
>>them to rust and/or corrode? I find them to be very
>> strange and even more so under a microscope. Some,
>>I recall, reminded me of micro iron meteorites. I
>>have pondered there presence for a long time and
>>have come up with a few theories, one being that they
>>are connected in some way to an impact crater.

There are there possible origins for the origins of
these "dark grey to black particles" depending from
where they are washing out. They are 1. man-made
particles, 2. heavy minerals in local sediments, or
pedogenic iron oxide concretions.

In the industrial parts of the United States magnetic
particles of man made origin can be quite abundant.
These particles are produced by diesel engines, coal
burning, coke production, steel manufacturing,
smelting, and similar processes. For example, Byerly
et al. (1990) discusses such spherules produced by
diesel engines and Matzka (1997) discusses conversion
of iron pyrite to small, magnetic iron spherules
during the burning of coal containing pyrite.

References Cited:

Byerly, G. R., J. E. Hazel, and C. McCabe (1990)
Discrediting the late Eocene microspherule layer at
Cynthia, Mississippi. Meteoritics. vol. 25, no. 2,
pp. 89-92.

Matzka, J. (1997). Magnetische, elektronenmikroskopische
und lichtmikroskopische Untersuchungen an Stauben und
Aschen sowie an einzelnen Aschepartikeln. Diploma Thesis,
Institute for Geophysics, University Munich.

A English summary of this can be found in "Case Study-
Anthropogenic Magnetic Minerals Combustion products:
ash from a Bavarian power plant" at:

Also, look at "Magnetic study of dusts collected in
and around Munich" found at:

Anthropogeneic Magnetic Minerals
fly-ash (combustion products), ferrous contaminatio

(NOTE: The above URL must be reassembled to work)

Second, the "dark grey to black particles" might be dark
colored, iron-bearing minerals that are washing out of
local glacial deposits. Because these minerals are often
significantly denser than the quartz and feldspar that
comprise the bulk of such sediments, they are
preferentially concentrated in thin layers when these
sediments are eroded and reworked by water and wind.
More information about heavy minerals can found standard
sedimentology textbooks such as:

1. Folk, R.L. (1980) Petrology of Sedimentary Rocks
Hemphill Publishing Company, Austin, Texas.

Heavy Minerals

2. Pettijohn, F. J., P. E. Potter, and R. Siever, R.
(1987) Sand and sandstone, 2nd ed., Springer, New York.

Third, any source of dark colored magnetic grains are
small concretions of iron oxide that form in many soils.

A discussion of the possible sources of magnetic
particles in modern sediments can be found in:

Bi, D. and R. D. Morton (1995) Magnetic spherules from
Recent fluvial sediments in Alberta, Canada;
characteristics and possible origins. Canadian Journal
of Earth Sciences [Journal Canadien des Sciences de la
Terre] vol. 32, no. 4, pp. 351-358.

However real cosmic spherules do exist and fall to Earth
all of the time. The problem is that they fall in such
small numbers relative to other sources that in historic
and surface sediments they are overwhelmed and masked
by man-made magnetic spherules and natural terrestrial
grains that are also magnetic.

1. Taylor, S., J. H. Lever, and R. P. Harvey (2000)
Numbers, types, and compositions of an unbiased
collection of cosmic spherules. Meteoritics and
Planetary Science. vol. 35, no. 4, pp. 651-666.

2. Lunar and Planetary Science XXXII (2001)
Thursday, March 15, 2001
9:30 p.m. UHCL
Cosmic Dust

Toft B. J. Chambers, R. Hassings, A. Godwin, R. Schauer,
A. Ross, J. DeBaer, R. Melchior, and J. Annexstad (2001)
Are Cosmic Spherules Found in Glaciogenic Sediments? A
New View of an Ongoing Investigation

Other related paper of interest.

Preliminary work on Spherule Bibliography by Gyorgy
Don Geological Institute of Hungary, Stefania ut 14,
Budapest, HUNGARY at:

Pictures of various types of magnetic grains can be
found in "Quaternary Climates, Environments and
Magnetism" by B. A. Maher and R. Thompson (Cambridge
University Press 1999) at:

Jeanne Devon asked:
> > Can anyone tell me anything about the general
> > composition of Sahara Desert sand? I have a couple
> > vials that I've been looking at on my lunch break.
> > Just out of curiosity, I held a Nd magnet against
> > the glass of the vial and several little black
> > specks jumped up on to the magnet. I looked at them
> > under a binocular microscope. I couldn't rule them
> > in or out as little micrometeorites.
> >
> > The orange color of the sand leads me to believe
> > that iron may be a factor in the sand's coloration
> > and composition, and that these specks may just be
> > ferrous minerals and nothing to get too excited
> > about.
> >
> > Has anyone come across this? Does anyone have any
> > information/thoughts/comments?

I suspect that the black grains in the Saharan sand might
be iron-bearing heavy minerals as discussed above and iron
oxides, which have accumulated on some grains. Mixed
in with these heavy minerals, there is the slight possibility
very might be very, very few grains of cosmic dust.
Recognizing these few brains will be very difficult.

Some starting references:

Alimen, H., J. Chavaillon, and S. Duplaix. (1964)
Mineraux lourds des sediments quaternaires du Sahara
nord-occidental. Serie Geologie no. 4, . Centre de
Recherches sur les Zones Arides, Paris, France. 74 pp.

Bellair, P. (1953) Diagramme mineralogique du Grand Erg
Oriental d'El Oued a Ghadames. Compte Rendu Sommaire des
Seances de la Societe Geologique de France. no. 5-6,
pp. 99-101. (Societe Geologique de France. Paris, France)

El-Baz, F., M. H. Slezak, and T. A. Maxwell (1979)
Preliminary Analysis of Color Variations of Sand Deposits
in the Western Desert of Egypt. In: Apollo-Soyuz Test
Project Summary Science Report. NASA SP-412, Vol. II,
p. 237-262.

El-Baz, F., and D. J. Prestel (1979) Desert Varnish on
Sand Grains from the Western Desert of Egypt: Importance
of the Clay Component and Implications to Mars. In Lunar
and Planetary Science XI, Lunar and Planetary Institute,
Houston, Texas, Part 1, p. 254-256.

Morales, C., ed. (1985) Saharan Dust. John Wiley & Sons,
New York, NY.

Prestel, D. J., J. E. Wainwright and F. El-Baz (1979)
Mineralogy and Morphology of the Coatings on Sand Grains
from the Gilf Kebir, Southwest Egypt. Transactions,
American Geophysical Union. vol. 60, no. 46, p. 872.
(November 13, 1979)

Herzig, C. T., and F. El-Baz (1980) The Effects of
Mineralogy and Grain Shape on the Color of Sands from
the Western Desert of Egypt, and Possible Applications
to Mars. Reports of Planetary Geology Program - 1980.
NASA Technical Memorandum 82385, p. 301-303.

Venzo, G. A., G. Marocco, G. Lenardon, and F. Princivalle
(1985) Grain size, roundness, surface textures and
mineralogical composition of recent desert sediments in
the Algerian Sahara. Giornale di Geologia. vol. 47,
no. 1-2, 3eme serie, pp. 221-235. (Istituto di Geologia
e Paleontologia. Bologna, Italy)

Worrall, G. A. (1969) The red sands of the southern Sahara.
Bulletin de Liaison - Association Senegalaise pour l'Etude
du Quaternaire de l'Ouest Africain. vol. 21; pp. 36-39.

Voelkel, J., and J. Grunert (1990) To the problem of dune
formation and dune weathering during the late Pleistocene
and Holocene in the southern Sahara and the Sahel.
Zeitschrift fuer Geomorphologie. vol. 34, no. 1, pp. 1-17.


Keith Littleton
New Orleans, LA
Received on Mon 19 Aug 2002 07:56:27 PM PDT

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