[meteorite-list] Meteorite Densities - Brother Guy

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Wed, 6 Oct 2010 15:04:05 -0500
Message-ID: <01504EDF7AB0416A8394173BF4A2AB8A_at_ATARIENGINE2>

Hi,

I thought this thread had died out. However,
while Wal-Mart playground sand would give good
results, you could try this: go to a construction
materials dealer or a hardware store and get
"White Flint Sand" (the ultimate playbox sand).
The last time I bought some, it was definitely
in 500-micron and smaller sizes.

Wash the sand first to remove dust and fines.
Then, sift some through a series of graduated
screens until you find the grade of screen
through which nothing passes. Use the next
coarsest screen to get the finest particles.
Unless you're measuring giant meteorites,
the amount of sand required is not great.

I searched for suppliers of volumetric glass
beads. Most such beads are 3 to 6 mm in
size and often irregular (and expensive). The
beads used in the lab procedure described
by Brother Guy were undoubtedly these:
http://www.amazon.com/3M-Empore-Filter-Inert-microns/dp/B0017Y3KF0/ref=sr_1_15?s=industrial&ie=UTF8&qid=1286391461&sr=1-15

They are: 3M Empore Filter Aid 400; Inert
Glass Beads Avg Dia. 40 microns; With Scoop;
1.5kg --- $107.49. 3M makes everything,
doesn't it? $200 to $300 ought to be enough
to measure meteorite density the same way.

Here's 100 to 150 micron beads at $42/pound:
http://www.amazon.com/Glass-Beads-0-1-0-15-mm/dp/B003NV7KOM/ref=sr_1_22?s=industrial&ie=UTF8&qid=1286391774&sr=1-22

Says the Wikipedia: "As the term is used by geologists,
sand particles range in diameter from 0.0625mm (or
1?16 mm, or 62.5 micrometers) to 2 millimeters." I
suspect White Flint Sand sifted for its smallest sizes
would likely fall into the 100-150 micron range.

["Buying some White Flint Sand, sifting, and then
measuring its particle sizes is left as an exercise for
the student."]

The smallest interstitial space of spheres in a lattice
is 26% of the volume of the spheres, of cubes, about
50%. That volume is the error you introduce into
the volume measurement (when multiplied by the
surface area of the meteorite. The smaller the particle
size, the smaller the error.

The error introduced by measuring an one centimeter
rock with 100 micron cubic particles (like sand) is
approximately 0.05%. The error introduced by
measuring it with 40 micron spherical particles is
approximately 0.01%. Even the error with half-
millimeter (500 micron) spherical particles is only
0.25%.

The bigger the meteorite, the smaller the error.
Doubling the size of the meteorite to 2 centimeters
cuts the error in half, and doubling again to 4-cm to
1/4th of the 1-cm error.

Measuring a less-than-2-inch meteorite with 100-micron
sand has an error so small, you're almost certain to make
a bigger error somewhere else...

Publish your results.


Sterling K. Webb
-----------------------------------------------------------------------------
----- Original Message -----
From: "Steve Dunklee" <steve.dunklee at yahoo.com>
To: <damoclid at yahoo.com>; <meteorite-list at meteoritecentral.com>;
<volcanoted at yahoo.com>
Sent: Wednesday, October 06, 2010 11:28 AM
Subject: Re: [meteorite-list] Meteorite Densities - Brother Guy


> or for the cheap people ordinary playground white sand purchased at
> wal mart cheers Steve
>
>
>
>
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Received on Wed 06 Oct 2010 04:04:05 PM PDT