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Hey Taliakerch, I always suggest not to wear any stone on permanent basis. They should be used need based. I use them only for healing purpose and never advise anyone to wear anything on permanent basis. Though there are some like Amethyst, Rose quartz, Selenite whose energies are very very soothing and can be used all the time.
Specific crystals rule the zodiacs but I still advise to use it purpose specific :-)

ok, Nainaz, thanks for explanation!
so one person can choose several stones and change them?
i saw persons who only wear 1 definite stone, saying "it's MY stone"-)

Yes dear, we can work with several crystals at one time, but when we wear something we need to be mindful. We can make certain universal crystals as My 1 Stone, like the Amethyst, Clear Quartz, Rose Quartz these work on overall basis for us.
There are times when we are stuck with certain patterns in life, like unknown fear in such cases one can keep 1 Crystal which works best for the person in this area, otherwise it's good to use them need based.
This is a very exhaustive subject my dear and there is no right and wrong about it, here you go more with the experiences. Like just 1 e.g. I so closely work with crystals but there is one Crystal Citrine which when I wear makes me very aggressive but if I have it around in my space it works beautifully with me. You keep discovering their magic as you more and more work with them.