[meteorite-list] Re: Chondrules Hardness

From: Pete Pete <rsvp321_at_meteoritecentral.com>
Date: Tue May 16 08:12:56 2006
Message-ID: <BAY104-F12A63EB550FF39DE445489F8A00_at_phx.gbl>

Thanks, guys.

That was very helpful, Elton!




From: Elton Jones <jonee_at_epix.net>
To: Rob McCafferty <rob_mccafferty_at_yahoo.com>
CC: meteorite-list_at_meteoritecentral.com
Subject: Re: [meteorite-list] Re: Chondrules Hardness
Date: Tue, 16 May 2006 00:53:25 -0400

Hello Rob, Pete

This has surfaced on the list a few times but long ago. Your assessment is
seems reasonable to me. One thought was that the chondrule would have the
hardness of its mineral of specific composition. (e.g an Olivine chondrule
would be the same as Fayalite 6.5-7 or feldspar as Orthoclase 6) with the
matrix on the order of Pyroxene/Bronzite/Hyperstene/Enstatie 5-6 Mohs etc.
I don't know that anyone actually tested that.

There are microhardness testers which should be capable of doing these
measurements and I , too would like to know. Perhaps someone with an
academic subscription could research any quantative work done on not just
chondrules but meteorite matrices in general.

Elton

Mohs and Hardness Trivia: " Hardness is the property of a material that
enables it to resist plastic deformation, usually by penetration. However,
the term hardness may also refer to resistance to bending, scratching,
abrasion or cutting." <http://www.gordonengland.co.uk/hardness/> Most
folks doing basic mineral identification are familiar with the Mohs(Mohs')
Scale. We take the published hardnesses for granted, it is usually a range
of values which that are just relative after all.

Several words of caution regarding the Mohs scale or any hardness scale for
that matter. The Mohs scale was developed in the early 1800s and based on
common minerals. Be it remembered that this is a scale using ordinal numbers
but the actual hardness increases at an increasing rate. (e.g gypsum-2 isn't
twice as hard as talc-1 and corundum-9 isn't 9/10ths the hardness of
diamond-10) As technology progressed, somewhere, someone added common items
for reference. Glass being 5.5 was based on non-tempered, soda-lime, plate
glass-- and all glasses aren't the same. Some volcanic glasses are in the 6+
range. There is some difference of opinion now that glass is 5.5 Mohs.
Plate glass has traditionally been 5.5 Mohs/143 Brinell but some glass's
tensile can be 325 Brinell_at_1000psi/ 700 Vickers: which is in the mild
tool-steel range. Some new references put the hardness at 6 Mohs. As to
knife blades and nails this reference was established long before cheap
pot-metal , 99 cent knife blades came into vogue. Files are harder than
normal steel. Normal nails not the panel brads are around 5, but I am hard
pressed to scratch glass with it most of the time. The new US penny is no
longer copper and I don't know if the English penny is/was comparable to the
US Alloy but "the penny" is considered to be a 3 Mohs.

I have a set of Mohs Index
minerals<http://teach.fcps.net/trt20/projects/EKU/Minerals/ID_Tests/MOHMIN.GIF>
at <http://teach.fcps.net/trt20/projects/EKU/Minerals/ID_Tests/> mounted on
rods with epoxy in a nice little case. Always remember when doing a hardness
test to start higher then you think it is because you'll wear out your
softer points a lot faster!

Ergo, when checking for hardness, insure your reference material/tool/point
is the hardness you believe it to be, that the hardness you are measuring is
the hardness definition you intend. Start with the harder points first.

Finally, the streak test is another common field test for mineral ID but it
is of little value in identifying most silicates, which is the primary
composition of chondrites and related clans. This is owing to the fact that
most all the silicates do not leave a colored streak even thought their
hardness is 5-6 and a streak plate is in the 7.5 Mohs range. Minerals over 6
in hardness tend to break into little grains along clevage planes rather
than smear. So we tend to call the streak "white" rather than clear. There
are also black streak plates for the purist.

Finally, a resource page for measuring hardness values and converting
scales, and etc.
<http://www.gordonengland.co.uk/hardness/brinell_conversion_chart.htm>

Rob McCafferty wrote:

>Well, My understanding is that normal glass is at
>about 5.5 and steel around 6.5 on the Moh scale.
>
>My own experience is that a chondrule rich meteorite
>will dull a steel file fairly quicky and I'd imagine
>that despite chondrules being supposed to be glass,
>they are much harder than terrestrial glass and it is
>the silicates which allow meteorite friability.
>
>I have not heard of a chondrule study but I don't
>think they'd be less than 6.0 on the Moh scale.
>
>Rob McC
>
>

______________________________________________
Meteorite-list mailing list
Meteorite-list_at_meteoritecentral.com
http://six.pairlist.net/mailman/listinfo/meteorite-list
Received on Tue 16 May 2006 08:12:47 AM PDT