Gems can scratch each other and the finish on your jewelry, so don't store them together or let them rub against each other. Most precious gemstones are much harder than the metal they are set in but allowing gemstones and jewelry to touch can result in damage. Pearls and opals, in particular, require special care. For most jewelry, mild soap and water applied with a soft brush is fine. However, do not use soap of any type with pearls, amber, coral, emerald, jade, kunzite, lapis lazuli, opal or turquoise. If you use a jewelry cleanser, make sure it is non-abrasive. Some gemstones may have been treated or enhanced by heating, oiling, irradiation or diffusion. The oil can get stripped away by cleaning, often making the gemstone change in appearance. If this happens, simply bring it in for re-oiling.