Because crystals pick up energies and vibrations from their environment and anybody who has handled them, regular cleansing should be a part of their maintenance.
Whether the vibrations your crystal has come in contact with were positive or negative - it will have an effect on your stone. Hence, why it is especially important to purify any new crystals that you purchase since their energetic history is unknown to you.
There are a number of techniques in which you can effectively cleanse and recharge your crystals. Below is a list of some of those methods. Apply these to new crystals, stones that cause feelings of irritability and gems that you frequently make use of.