[meteorite-list] Pallasite Vs Mesosiderite

[al mitterling]

Hi Pete and all,

Pallasites are named from their discover the German naturalist Protr Pallas 
and are NOT named from the asteroid 2 Pallas. As said previously they are 
stony-iron material containing olivine crystals that are enclosed in an iron 
metal. The crystals are often of gem quality. Their is variation on the 
amount of crystal to iron metal ratio. Sometimes having more crystals and 
less metal and sometime just the opposite. Some specimens like Glorieta 
Mtns. the crystal material simply runs out and you are left with all metal. 
The Olivine in most pallasites are rich in magnesium, the metals have nickel 
(of course) germanium, and gallium contents that are very similar to the 
iron meteorite group (IIIAB) which is the most populous and contains over 
200 meteorites.

There are three groups of Pallasites, Eagle Station, Kentucky is one that 
has iron rich olivines and metals which are composed differently from the 
other iron groups. Suggesting similar formation but from a different parent 
body.

Mesosiderites are stony-irons composed of nearly equal amounts of metal and 
silicates. It is thought that the iron and the silicates formed from two 
different parent body sources and then through collision mixed and 
solidified. The stony material in mesosiderites consists mostly of pyroxenes 
and plagioclase. Many of the fragments that contain the silicate are similar 
to eucrites, diogenites, and howardites or come from an achondrite body. 
Missing in mesosiderites (in any abundance) is olivine, the most abundant 
mineral in ordinary chondrites. So mesosiderites are mixtures of core 
material and crust materials from a highly differentiation parent body. The 
stony material in these have been recrystallized from possible mixing with 
molten iron. Age for these are the same as iron and other achondrite bodies 
suggesting that the formation occurred early on in the solar system history. 
There are something like 40 different mesosiderite find and falls. The 
cooling rate is interesting as these cooled very slowly and no explanation 
as how they could of cooled so slowly unless they formed within a very large 
asteroid parent body.

Best!

--AL Mitterling

Mitterling Meteorites

----- Original Message ----- 
From: "Pete Shugar" <pshugar at clearwire.net>
To: <meteorite-list at meteoritecentral.com>
Sent: Monday, December 29, 2008 2:55 AM
Subject: [meteorite-list] Pallasite Vs Mesosiderite


> OK, to me they look the same when you cut them open.
> What gives? Does one have more metal or more olivine
> than the other?
> Brahin is a Pallasite with beautiful olivine and metal to hold
> it all together.
> Altho I have as yet to see a slice of Vaca Muerta, a mesosiderite, just
> looking at it
> I can see what appears to be olivine crystals.
> Would someone chime in with a concise defination of the two, please?
> Thanks for the help.
> Pete
>
>
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