Crystal Cleansing
There are many ways to "cleans" or "neutralize" your crystals. The main idea is to remove the emotions and intentions that you have charged into your crystals so they are clear for next time. Some stones will even be so fully charged that they start to splinter or crack! Here are a few ways to clear your crystals before you get to that point.
With other crystals:
Selenite is a fan favorite here. Placing your stones in a selenite bowl or on a wand/bar of selenite is a goes-anywhere solution to bringing your stones back to zero. It is also great for a quick fix considering it takes very little time and can be done anywhere, though it is said that leaving them overnight is best. Just make sure your stones are touching the selenite and voila! Your crystals are ready for recharging.
Moonlight:
Any moonlight will do! Place crystals on a windowsill so they are exposed to moonlight and leave overnight. There is no specific type of moonlight that is best for cleansing, though the new moon is considered the best time to recharge your crystals, set new intentions, and renew your energy. Ironically, a new moon is when you cannot see the moon at all, but the alignment of the earth, moon, and sun make it an ideal time to renew.
Water:
Running your crystals under a faucet or dipping the crystals into a small bowl of water. Water cleansing for crystals can be tricky. NEVER use salt water, NEVER use on non-polished crystals or geodes, and NEVER use water on any crystal ending in "-ite" (Thank you, Peggy for that tip!) due to the stones being too porous. In other words, calcite, hematite, flourite...etc. should be cleansed with water.
Sunlight:
Another good option, but not for all stones or with repeated use. Most crystals are found underground and out of direct sunlight making their colors vibrant and bright. If left repeatedly in the sun crystals have a tendency to fade over time. Again, not the worst option (especially in a pinch), but avoiding constant sun exposure is a good practice. If you find that this is the best option for you only leave the crystals to bask in the sunlight for a few minutes and avoid any timeframe over 30 minutes+.
Smudging:
Ah! One of the best known and most popular options for clearing your crystals is the smoke-it-out method. Sage is always a popular choice and has been used for centuries to clear energies out of crystals. Herbs, incense, Palo Santo, and incense resins are also great options for the smudging process. The smoke creates a wonderful visual of taking any negative emotions and releasing them. Always make sure there is an exit for the smoke and intentions by opening a door or window. Also, it is best to use a catch- either a fire safe bowl or shell to catch the ash. Cleanse yourself before you cleanse your crystals. Set your intentions, and go for it. It is a great meditative practice that can be done whenever you have a few minutes (which you should build into your life at minimum weekly! Don't ever forget to take care of YOU).
There are always ways to neutralize the powers contained in your crystals. These seem to be the most ideal and practical options for wherever your are. It is a best practice to reset your mind as you reset your crystals so both are ready to take on anything that comes your way.