There's a terrific paper by Al Cuoco, Paul Goldenberg, and June Marks called Habits of Mind: An Organizing Principle for the Mathematics Curriculum, which deals with the differences between algebra and geometry. Of course there are other parts of mathematics with distinctive patterns of mind -- probability and statistics, combinatorics, etc. -- and not everyone will agree with everything they say, but it's a good place to start.
I don't believe it's appeared anywhere, but if you're interested you could write to them at EDC.
==================================== Judy Roitman, Mathematics Department Univ. of Kansas, Lawrence, KS 66049 firstname.lastname@example.org =====================================