I would strongly recommend you cleanse your crystals of unwanted vibrations/energies from other people or surroundings, absorbed during its findings, mining, packing, transportation, unpacking, displaying, before it has reached you.  As crystals absorb energy, you may feel this potential chaotic or lack of energy within the stone within yourself.

Once stones absorb non-positive energy, and aren’t cleansed, the next person that uses it can absorb that non-positive energy.  Or if you are the only user, your stone can get so absorbed that the non-positive energy can start draining you.  When a crystal/stone is ‘full’ the stone may feel different to you, maybe heavier, or maybe you just can’t figure it out, definitely time to cleanse it.

Crystals/stones have been known to break in two (or more pieces) when over filled with non-positive energy.  If this happens, the stones are still usable after cleansing.  The break may change the attraction within you, or alter the properties somewhat. 

If after you’ve cleansed it, you don’t feel right with it, your need for this stone may be at an end, and it may be time to gift it to someone else, or give back to Mother Nature.  Not recommended to throw stones/crystals in the garbage, as they are precious gifts from Mother Earth. Gift them back outside.

Some options are:

• Place crystal in organic brown rice (or organic wild rice). Option to leave them in the rice until the next time you need them.
  
• If you are familiar with Reiki, Reiki is also an excellent way to cleanse crystals, as well as asking our Universe to cleanse crystals.  Hold crystals in hand, set intent to cleanse crystals, and pray and/or draw symbols on stones.
• If you have a crystal/stone that is self-cleansing  (e.g. citrine), it may cleanse others.  Place near each other.
• Gently/carefully pass them over a candle flame a couple of times.
• Place crystal outside in a moonlight phase, or outside for a 24 hr cycle.
• Some crystals are safe to run under water for a minute or so, or place in salt water for a short time.  It’s best to read up on the specific crystal.
• Gently pass them over cleansing incense, suggested choices are (but not restricted to) sage, sandlewood, lavender. 
• Always an option to do a search on the internet for other options.

How long to cleanse? This is a tough question to narrow down.  When your stone/crystal is cleansed, it should feel better somehow..maybe even lighter.  Your intuition may pick up that it’s energy is radiating stronger.  Various dynamics may determine how long.  How long since the last cleanse. How much it has absorbed.  Different methods of cleansing may have different timeframes.  If using rice, how old is the rice? Should it be replaced?

Think of it this way, when we need a vacation, sometimes we just need a few hours alone time, and sometimes we would love a days or weeks.  This is comparable to how long to cleanse your crystals, it all depends on how much they've been working for you.

Time to move on: There may be a time when one of your precious stones/crystals is done serving you/your Higher Self.  You may find you don’t resonate with it anymore, or you’ve forgotten about it.  If this happens, and you’re ok with it, gift it to someone who may need it, or someone who has noticed it and has complimented/commented on it. Remember to thank the stone for all it’s done for you.