[meteorite-list] Re: Chondrules Hardness

[Elton Jones]

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
>  
>