[meteorite-list] Iron Meteorites IIG Group

[David Weir]

Hello Mike,

I have not yet read an official publication on the IIG proposal for the 
five members you mentioned, but perhaps I just missed it. I presume it 
will be accepted when published by the present-day dean of irons.

Here is a synopsis of the classification parameters for the various iron 
chemical groups:

The main groups are resolved based on a congruence in the percentages of 
nickel (Ni) and certain trace elements, mainly germanium (Ge) and 
gallium (Ga). These two are especially useful because of their wide 
range across the entire iron spectrum, but narrow range within specific 
iron groups. Some other elements used to resolve groups are iridium 
(Ir), copper (Cu), cobalt (Co), and gold (Au); each resolved group 
represents an origin from a unique asteroid accreted in a unique nebular 
region. The occurrence of either positive or inverse correlations among 
the ratios of Ge, Ga, Ni, and Ir serves as a useful grouping 
determinant. Likewise, the consistent variation of certain elemental 
concentrations in the irons serves as a grouping determinant. Another 
useful, but less precise, grouping method is based on similarities in 
the macrostructure of etched irons, and is influenced by the bulk nickel 
content of taenite in association with the cooling rate. This feature 
primarily categorizes irons as either hexahedrites, octahedrites, or 
ataxites.

David