Can gemstones be cleaned with ultrasonic cleaners?

Hard, untreated gemstones like diamonds and sapphires can often be cleaned without trouble in ultrasonic cleaners. But many other stones will crack, shatter, or lose their protective treatment layers. Porous, heavily included, or organic gems should not be placed in ultrasonic vibrations under any circumstances.

Ultrasonic cleaners use high-frequency sound waves, which then make microscopic bubbles that actively scrub away grime. That cavitation effect becomes pretty intense, and it can expand existing natural inclusions inside fragile stones like emeralds, tanzanite, and tourmaline, causing sudden structural failure. Also, the vibration plus the heat can strip protective oils and fracture-filling resins from treated stones, changing their look permanently. For all fine jewellery, the gentlest method is still mild dish soap with warm water and a soft brush, nothing more.