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
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