Gemstones only improve the health and condition of both the seller and the wearer possibly.
Yes, it acts as a placebo, which in turn has a positive effect. But this cannot be attributed to the gem, it would be effective in the form of a ring or pendant made of precious metal, which in turn is being worn by a person with positivity and hopefully it is really helpful.
Gems do not attract gravity from Saturn or Jupiter, nor do some cosmic rays. If diamond is effective, then other gemstones also .