[meteorite-list] Magnet canes are evil

From: David R. Vann <drvann_at_meteoritecentral.com>
Date: Tue, 24 Aug 2010 14:23:37 -0400
Message-ID: <CBCD31405B664E21AA8D329964FE4508_at_sas.upenn.edu>

Magnetic canes and similar can add to, alter or destroy the magnetic imprint on
a meteorite. So, however, does the Earth's own magentic field after a time (OK,
a long time, but not *that* long). In general, only very recently fallen
meteorites are useful for magnetic domain studies. However, a cane's effect can
be restricted to measurable surface effects if the meteorite is large enough. A
few magnetic studies have been done, usually on falls (e.g. Richardton, Berduc,
Allende). Some have determined paleomagnetism, in spite of the overprint (which
can be recognized). In fact, attempts have been made to estimate Mars' magnetic
field based on the micromagnetic domains within e.g. nahklites. Unsurprizingly,
most of the analyzed samples are Antarctic ones, where anthromagnetic imprints
have been avoided. One of the most interesting things to come out of this is
that early planetismals may have been large enough to have a dynamo, i.e. their
own magnetic field.

This is an interesting summary of some of what is known:

Paleomagnetic Records of Meteorites and Early Planetesimal Differentiation
 SPACE SCIENCE REVIEWS Volume: 152 Issue: 1-4 Pages: 341-390
Published: MAY 2010
Weisss, et al.

Abstract: The large-scale compositional structures of planets are primarily
established during early global differentiation. Advances in analytical
geochemistry, the increasing diversity of extraterrestrial samples, and new
paleomagnetic data are driving major changes in our understanding of the nature
and timing of these early melting processes. In particular, paleomagnetic
studies of chondritic and small-body achondritic meteorites have revealed a
diversity of magnetic field records. New, more sensitive and highly automated
paleomagnetic instrumentation and an improved understanding of meteorite
magnetic properties and the effects of shock, weathering, and other secondary
processes are permitting primary and secondary magnetization components to be
distinguished with increasing confidence. New constraints on the
post-accretional histories of meteorite parent bodies now suggest that, contrary
to early expectations, few if any meteorites have been definitively shown to
retain records of early solar and protoplanetary nebula magnetic fields.
However, recent studies of pristine samples coupled with new theoretical
insights into the possibility of dynamo generation on small bodies indicate that
some meteorites retain records of internally generated fields. These results
indicate that some planetesimals formed metallic cores and early dynamos within
just a few million years of solar system formation.

Contact me off-list if you are interested in the PDF

So, best not to pick them up by magnetic cane if you want paleomagnetic data.
But note, plenty of meteorites that cannot be picked up by a magnet have relic
magnetic fields in the stones, whether in tiny ferromagnetic bits or in the
other minerals (magentic microdomains). Also, unless the original signature has
been destroyed, it is still just possible to recover the signature from
"beneath" a stronger, localized imprint caused by a magnet. Just don't touch all
of the stone with a magnet... (little stones, forget it)



David R. Vann, Ph.D.
Department of Earth and Environmental Science
THE UNIVERSITY of PENNSYLVANIA
240 S. 33rd St.
Philadelphia, PA 19104-6316
drvann at sas.upenn.edu
office: 215-898-4906
FAX: 215-898-0964


| -----Original Message-----
| From: meteorite-list-bounces at meteoritecentral.com
| [mailto:meteorite-list-bounces at meteoritecentral.com] On
| Behalf Of Meteorites USA
| Sent: Tuesday, August 24, 2010 1:45 PM
| To: meteorite-list at meteoritecentral.com
| Subject: Re: [meteorite-list] Magnet canes are evil
|
|
| Curious about the magnetic properties of meteorites as well.
| We all know
| that you can magnetize metal just by placing it near a
| powerful magnet.
|
| I read yesterday in Richard Kowalski's post about Brother Guy
| Consolmagno's visit to Tucson. Dr Concolmagno's research also
| includes
| the study of magnetic properties of meteorites. I'm sure he's not the
| only person to study these properties, but it got me to
| thinking about
| it. If one does in fact use a magnet cane on a meteorite, do
| you impart
| any magnetic field into the meteorite? I would think yes,
| even if it is
| small on a scale only readable by the most powerful equipment.
|
| My question is does it cause problems with analyzing/testing?
| Is this a
| form of contamination?
|
| My question would of course then be... Why use a magnetic cane at all?
|
| If you think about it, we're "taught" NOT to remove a meteorite from
| it's original location until we get in-situ photos, and record GPS
| coordinates of the find. If you use a magnetic cane, the
| meteorite will
| be removed from it's ancient resting place as it "snaps" onto
| the magnet.
|
| Eric
|
|
|
|
| On 8/24/2010 10:10 AM, Matson, Robert D. wrote:
| > Mark wrote:
| >
| >
| >> As soon as everyone stops using metal detectors and magnet
| canes to
| >> look for meteorites then the first Lunars in Europe or USA will
| >> eventually be found, .... until then!
| >>
| > I have never used a magnet cane, nor will I ever, and I
| always advise
| > new hunters against their use. A magnet cane is basically
| an H-, L-,
| > iron, and stony-iron filter. I sometimes carry an LL6 with
| me to the
| > desert on the off-chance I'll run into someone using a magnet cane.
| > That usually "cures" them. ;-)
| >
| > --Rob
| > ______________________________________________
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| >
| >
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Received on Tue 24 Aug 2010 02:23:37 PM PDT