Onyx is a gemstone that is a variety of the mineral chalcedony. When cleaning and taking care of this stone, you should keep in mind that onyx is relatively soft (6.5-7 on the Mohs scale of hardness), porous and easy to damage.
It is worth noting that a lot of the stones sold as onyx today are actually dyed agate. Nevertheless, even if this is the case with your gemstone, it should be cleaned using the same methods applicable to real onyx.

Black onyx
Cleaning Onyx Gemstones
Cleaning onyx jewelry is pretty straightforward: Just use a soft, dry cloth or a soft brush to wipe any dirt off your gemstones.
You can also use a little water to moisten the cloth and make the cleaning easier.
Don’t wet the stone or soak it in water, however, as onyx is porous and absorbs liquids easily.
After the cleaning, dry the stone with a soft cloth.
What to Avoid When Cleaning Onyx
Since onyx is very absorbent, you should not use any cleaning chemicals on it as they may seep into the stone and cause it to change its color.
Although ammonia is commonly used to clean jewelry, you should not use it on onyx. Even using soap or mild dishwashing liquid is not recommended.
Do not put onyx in ultrasonic cleaners as the cleaning liquid and ultrasound vibrations can be harmful to the stone.
Related: Check out this rich selection of onyx jewelry.
Cleaning the Settings of Your Onyx Jewelry
To clean the setting that holds your onyx stone, you should use a method that is appropriate for the metal your ring or other jewelry is made of.
However, since onyx is such a vulnerable gemstone, it unavoidably limits you in how you can clean the other parts of your jewelry. As already mentioned, be careful not to use any harsh chemicals that could harm the stone.
If your onyx ring is made of silver, for instance, it is not recommended to drop it in a solution of water and baking soda to remove tarnish, as you could do if the piece was made from silver only.
If you are using water and soap to clean your gold onyx jewelry, for example, be careful not to wet the gemstone; also, don’t allow any soap to come into contact with your onyx.
In general, the safest way to clean the metal parts of your onyx jewelry is to use a soft cloth and a little water. Use a soft brush to clean the hard-to-reach areas of your setting.
If you are polishing your jewelry using a polishing cloth, do not use it to also polish the onyx gemstones set in the piece.
Care When Wearing Your Onyx Jewelry
Since onyx is a stone that can scratch, chip or crack easily, make sure you avoid hitting or bumping your onyx ring or other jewelry when wearing it.
Always put on your onyx jewelry after you’ve already applied any makeup or other chemicals such as hair spray or perfume, which can be potentially harmful to your gemstone.
Take your onyx rings off when doing any housework: Water and other substances used in cooking and cleaning can damage your stone.
Do not wear your onyx jewelry when taking a bath or when swimming.
Storing Onyx Gemstones
Make sure your onyx jewelry is stored in a way that protects it from damage. Wrap your onyx pieces in a soft cotton or velvet cloth to keep the stones from being scratched by other harder gemstones or metals.
You can use individual jewelry pouches such as these for each item. For further protection and convenience, you can store your jewelry in a jewelry box with separate compartments — here is a jewelry box that is very popular.