Duplicating categories & SEO ramifications

My jewelry site has a "Shop by Gemstone" top-level category as well as top-level categories for "Necklaces", "Bracelets" and "Earrings".

Under my "Shop by..." category, I have sub-categories of the gemstones like, "Amber", "Amethyst", etc. Under each of these I have sub-sub-categories like, "Amber Necklaces", "Amber Bracelets", "Amber Earrings".

In my remaining top-level categories, I am wanting to add the same sub-sub-categories as above ("Amber Necklaces", "Amber Bracelets", "Amber Earrings") as sub-categories, using the exact same attributes, including SEO Keyword so the exact same category content appears. In essence creating the effect of assigning children categories to multiple parent categories.

Does anyone see any particular SEO issues with doing this? I have added code to canonicalize all category URLs. I'm not seeing any obvious functional issues, but am concerned with negative SEO ramifications and/or search engine penalties.

Would appreciate feedback or thoughts. Anyone else done this with success?

Not sure why you want to duplicate categories? Why not just do a custom menu and link to the same category in multiple places instead of duplicating them completely?

I hand code all my top menus so I can do things like this myself.

I suppose that is an option but try to avoid hardcoding for obvious upgrade reasons. I could attempt to write a vQmod for it, but it almost seems easier to go the duplicate route.

Thanks for the suggestion. Anxious to hear other thoughts, pros/cons.