There's thousands of bloggers who write about jewelry: http://www.google.com/search?sourceid=chrome&ie=UTF-8&q=jewelry+inurl%3Ablog
There's cool stuff like this:
http://www.huffingtonpost.com/2010/01/20/geeky-jewelry-the-nerdies_n_429408.html
http://mashable.com/2010/08/05/geek-jewelry/
Videos with hundreds of thousands of views: http://www.youtube.com/results?search_type=videos&search_query=jewelry&search_sort=video_view_count&suggested_categories=26%2C10%2C24
There's no niche, IMO, that's too boring or too stale for great content.
