Natural crystals include amethyst, citrine, rose quartz, and tourmaline. Crystals are generally durable, but can still break or get worn away by harsh soap and scrubbing, so make sure you treat them gently. Start by wiping your crystal with a soft cloth dipped in warm water. If that doesn't restore its shininess, you can use a more thorough cleaning method. But before you do, please check whether your crystal is porous or non-porous (for examples of porous and non-porous stones, see the Semi-Precious Stones entry below). Assuming your crystal is non-porous, start by mixing 1/2 cup warm water, 1 teaspoon rubbing alcohol, and 1/2 teaspoon detergent-free dishwashing liquid. Dip your crystal in the liquid and let it soak for 30 seconds to one minute, then rinse it off briefly under lukewarm running water. Dry your crystal with a clean cloth, and it should be good as new!