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I recently encountered the existence of the "Niggli" norms in a 1930s paper by Read on some gabbros from my area. With no discussion of this norm-calculating method, I'm going to have to do some research to document it. Read was a smart cookie, and would have had some good reason for using Niggli norms instead of CIPW norms. Aidan Karley (talk) 09:25, 10 December 2008 (UTC)
So much for keeping up to date. Back in 2014!
A program (evidently for calculating norms from analyses) called [1], from .CZ, mentions Niggli norms in it's help pages, which suggests the author is in a position to explain the differences. I'll contact him.
From a book on Google Books Over Magma, 2003 comes the quote that "Like almost everyone else, Niggli (1931) recognised that the CIPW classification was really a classification of magmas, and therefore not suited to the needs of petrographers." Which may well explain why Read was using it.