Many pagans and witches use crystals and gemstones in their practice. They tap into their energies, using them to enhance spells or meditation, calling on them to represent the element of Earth (or sometimes fire), or wear them as talismans for protection, and much more besides. Crystals are some of the hardest working items in a witch’s toolkit! So it makes sense that, like any other hard-working object or person, crystals need to be taken care of.
There are many different methods of charging crystals, and also cleansing them, which is a subtley different but closely related concept. For me, I like to cleanse crystals with incense, and charge them mostly by moonlight. Some people prefer to charge their crystals by sunlight, but it is important to note that several crystals cannot be left in sunlight for long periods as their colours will bleach. Of the crystals I work with these would include amethyst, aquamarine, aventurine, sapphire and rose quartz. Equally some people like to cleanse their crystals with water, but again this method is not suited to all stones as some will be damaged by prolonged contact with water, or may leech elements into the water which are not beneficial to you - for instance Malachite leeches copper.
Whenever I receive a new batch of crystals, including those I use for jewelry making, I make a point of cleansing them with incense as soon as possible to remove traces of any other energies they have picked up on route to me, either from previous owners or anyone handling them along the way. Then I will lay them out under the next full moon, often also with incense burning nearby, to allow their energy to be replenished. You can find your own rituals and ways of enhancing your work with crystals, but I definitely advise you to research the specific stones to ensure they are not negatively affected by the process.
I hope this has been helpful!