I do believe in their healing powers, not in a magical or mystical sense, but in terms of their colours (the effects of colour and the associated light waves on the brain is well known) and also vibrations that can come from them. Everything on this planet vibrates and it's a case of finding the right vibrations to sympathise with or enhance your own vibrations.
And then there's the placebo effect. I have a lot of time and respect for that! If something helps, then why mock it or try to discredit it?
Having said that, one of my fave shops is 'The Rock Shop'. It has THE most beautiful jewellery made from Nature's rocks. In all the time it's been trading, I've NEVER walked out of there without having purchased SOMETHING, maybe I shouldn't walk IN! Lol!
I have a chunk of.Rose Quartz and I do believe it makes a difference. Perhaps because the look of it pleases me I feel better likewise the lump of amethyst. I also have various bits of rock on a bookshelf I am intrigued by them - if they have 'powers' - fine with me. Each unto his/her own!