It's hard to believe that a derailleur can weigh 500g, but, if you want that kind of thoroughly grounded, reassuringly solid, gravitas, you have a surprising number of options.

Here is a selection of derailleurs that weigh over 450g. I have listed them in descending order of weight. I have not concerned myself with whether the weight shown includes the hanger plate etc. etc.. Such trivial concerns are for flighty weight weenies, not for substantial gentlemen of unarguable substance.