[meteorite-list] Meteorite or not???

From: Matson, Robert <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Thu Apr 22 09:41:07 2004
Message-ID: <AF564D2B9D91D411B9FE00508BF1C8692C5EEF_at_US-Torrance.mail.saic.com>

Hi Craig,

> I am from Chapleau, Ont, Canada and believe that I have found a meteorite
and have
> been trying to find someone whom can accurately verify and classify. Here
are the
> reasons that I think it is a meteorite:

> The specimen was found in an area comprised of sand and gravel(granite
based) and
> it is black which is what caught my eye.

Black can be good and bad. Black is good if it is clearly a fusion
crust, but a bad sign otherwise. Most meteorites (that have spent
any time on the ground) start to weather to brown in fairly short
order.

> It is fairly dense, my calculations are- mass 69 grams, volume 23.287
cubic cm,
> for a density of 2.963 grams/ cubic cm

This is light for an ordinary chondrite, but not a 100%
shop-stopper.

> a magnet sticks to it

Good, but not conclusive by itself. Magnets will also stick
to magnetite (which is also black), hematite and basalt.

> black surface with evidence of thumb prints but not real obvious as in
some
> specimens, all edges are rounded

Based on the image, I probably wouldn't call these thumbprints.
But thumbprints aren't a requirement -- particularly for a
meteorite candidate of this size.

> a few locations have a fusion crust( rustly brown in colour) with melt
lines showing
> The majority of the surface is black except where the fusion crust is.
The interior
> (small section is broken off) is also black but a bit duller than the
exterior.

This (the interior) is generally a bad sign. If the black
exterior truly represents a fusion crust, then it should
only be a maximum of a couple millimeters thick. The interior
should be noticeably lighter, with few exceptions.

> Not silvery or metallic.

Given the low density, you would not want to see a uniformly
metallic or submetallic interior -- that would be a bad
sign. Of course, you'd *prefer* to see little specks of
silvery metal in a stoney matrix.

> Where the section is broken off there is a vug which is supposedly not
conducive
> to a meteorite

Vugs are not uncommon in irons, but then this isn't an iron.

> The surface also has scattered, small, very shallow, circular depressions
that
> range in size of a tip of a pin(less than a mm) to up to a mm or two. A
few of
> these depressions holes are filled with a whitish material.

Unfortunately, this is the biggest counter-indicator for you.
Tiny holes in the surface is not at all typical for a
meteorite.

Based primarily on the image you provided, the density estimate,
and the magnetism, I'd say you've probably got a fine-grained
olivine basalt, with the black color coming primarily from
magnetite as a partial constituent. If you do a streak test
of this rock (scrape it against a piece of unglazed white
porcelain -- like the back of a porcelain tile), I expect the
streak will be dark gray. Most (but not all) meteorites are
hard enough that they produce a white streak -- i.e., they
are harder than the streak plate material.

But the best test you can perform is to file down a side a
millimeter or two deep to see what the fresh interior looks
like. If it looks relatively uniform black, it's very unlikely
to be a meteorite.

Best of luck,
Rob
Received on Wed 07 Feb 2001 11:07:58 PM PST