Enstatit Chondrite: Kein Unterschied zwischen EL und EH ?

[ben.g]

Hallo Forum. 

Ich habe gerade mal in dem MaPS Supplement mit den Abstracts der Vorträge aus Nancy gestöbert. Da ist mir eine Arbeit über Enstatit-Chondrite (EC) ins Auge gefallen.

In den Systematiken wird ja zwischen EH und EL unterschieden, je nach Eisengehalt. Möglicherweise ist das kein gutes Differenzierungskriterium. Ich zitiere hier mal Auszüge aus der Arbeit:

EH and EL Enstatite Chondrite Physical Properties: No Difference in Iron Content.
Robert J. Macke SJ, Melinda L. Hutson, Daniel T. Britt, Guy J. Consolmagno SJ
72nd Annual Meeting of the Met. Soc.;  2009 Nancy, France (#5047)

Introduction:
(...) The most widely used system divides the ECs into two groups, EH and EL, based on iron content. (…) In many cases, the bulk compositions were determined from samples significantly smaller than 10g, while ECs are rich in large clasts and can be heterogeneous at this scale.
Grain density and magnetic susceptibility measurements of larger samples can resolve this issue, as they provide a quick and non-destructive measure of average whole-rock iron content.

Results:
(…) we have measured density, porosity and magnetic susceptibility of 26 stones from 16 different Ecs. (…)
- Average grain density for EH is 3.61±0.14 g/cm³, and for EL is actually slightly higher, at 3.65±0.24 g/cm³; statistically the two groups are indistinguishable. (...)
- Porosities from all but one sample were between 0 and 6.4%. (...)
- Average logχ for EH is 5.21±0.46 and for EL is 5.38±0.30. Eliminating outliers, average log χ’s for EH and EL agree at 5.45.

Discussion:
The EH and EL chondrites are indistinguishable in all of the physical properties tested: density, porosity, and magnetic susceptibility.
We conclude that there is no systematic difference in iron content between EH and EL chondrites. (…)

Falls das bestätigt wird, kann man sich diese Unterklassifizierung getrost sparen.

Gruß
Ben