[meteorite-list] Iron Meteorites IIG Group

[Mike Fowler]

Hi List,

I recently saw a small Tombigbee iron on ebay incorrectly listed as  
ungrouped, which it was, till the the Guanaco meteorite was  
determined to be the 5 member necessary to form a group.

My question is this:  Why IIG?  Why not IIIG, or IVC?  or some other  
designation?

Thanks,

Mike Fowler
Chicago