Maybe that's 'cause we live in Houston, and it's pretty darn humid here. :)
Pardon me for barging in but precious opals are my specialty. I've been cutting/selling them for 40+ years and have learned a little about them.
Just treat your opals with respect. They're more delicate than other gems and can't take hard knocks. They do have relatively high water content. If you live in a very dry area give them a soak in water occasionally to rehydrate them or, better, store them in a plastic bag with damp cotton inside. Chances are your opal won't crack anyway but it's like eating chicken soup for a cold -- it can't hurt!
Do NOT store opals in safe deposit boxes! Bank vaults are dehumidified to prevent paper from mildewing and opals need a little humidity. Opals need repolishing now and then: they're soft and the polish can wear away. The main reason for repolishing is appearance: you want all the beautiful play of color you can get. Most opals can be repolished without removing them from their settings.
Enjoy those marvels of nature!
Thanks Bernard!