Search any gemstone to see its Mohs hardness, toughness, and how to clean and store it safely — before you reach for the ultrasonic cleaner.
Hardness and durability figures are general guidance for typical, untreated material — treated, dyed, filled, or heavily included stones can be more fragile than the species' textbook values suggest. When in doubt, clean with a soft cloth and warm soapy water only.
Mohs hardness measures resistance to scratching: diamond tops the scale at 10, while talc sits at 1. But hardness is not toughness. Toughness is resistance to breaking and chipping — and some quite hard stones are genuinely brittle. Topaz, at 8 on the Mohs scale, has perfect cleavage and can split from a single sharp knock, while jade, only 6.5–7, is so tough it has been carved and worn for millennia.
This is why the ultrasonic cleaner question can't be answered by hardness alone. Emerald (7.5–8) is almost always fracture-filled and should never see an ultrasonic bath, while garnet (6.5–7.5) tolerates one easily. When in doubt, warm soapy water and a soft brush remain the safest cleaning method for every gemstone on this list.
The Mohs scale ranks minerals from 1 (talc, scratchable by a fingernail) to 10 (diamond, the hardest natural material) by which scratches which. It's a relative scale, not a linear one — diamond is roughly four times harder than corundum (9), which in turn is far harder than quartz (7). Everyday dust contains quartz, so any stone below 7 will slowly dull from normal wear.
Hardness is resistance to scratching; toughness is resistance to breaking and chipping. They behave independently: topaz is hard (8) but brittle due to perfect cleavage, while jade is only moderately hard (6.5–7) yet exceptionally tough. For everyday jewelry, toughness often matters more than the Mohs number.
Generally safe: diamond, spinel, garnet, quartz (amethyst, citrine), and chrysoberyl. Avoid entirely: emerald (fracture-filled), opal (water content), tanzanite and topaz (cleavage), turquoise and lapis (porous), pearl, amber, and coral (organic). Untreated sapphire and ruby are usually fine, but fracture-filled stones should never go in ultrasonic.
Warm water with a drop of mild dish soap, a soft brush for settings, and a lint-free cloth to dry. This method is safe for every species in this database. Avoid harsh chemicals, sudden temperature changes, and — for porous or organic gems like opal, turquoise, and pearl — even prolonged soaking.