The term crystal includes gemstones or precious stones and semi-precious stones. Crystals can be worn as pendants or as rings; or carried in your pocket.
A six-pointed crystal (many are long, polished stones with six sides and often have a pointed or rounded end) balances the upper and lower chakras. The six-pointed crystal also balances and strengthens the upper, middle and lower sections of the aura.
As a pendant, a crystal is preferably worn between the heart and the throat.
As a ring, it is better to wear the crystal on the little finger or the middle finger; either on the left or right hand.
Garnet is preferably worn on the right hand and is used for strengthening the aura and for psychic self-defense. People who are pessimistic or rather negative should not wear it because they tend to attract misfortune. However, if worn by people with a wholesome and optimistic attitude, garnet tends to attract good luck.
Citrine is good for psychic self-defense. It should also be worn on the right hand.
Green tourmaline or emerald is recommended for healers, physicians and psychotherapists. It should be worn on the right hand.
Diamond is a very powerful crystal for psychic self-defense and is preferably worn on the right hand. Diamonds with inclusions, slightly yellow diamonds or a cluster of small diamonds on a ring will do. The lesser expensive diamonds will provide a similar degree of protection as will expensive diamonds.
Crystals should be cleansed before wearing as a pendant or ring. One of the easiest methods is to wash the crystal with soap in running water for about a minute or more. You may also use the fingers to rub it under running water with an intent to cleanse it of all impurities. Alcohol can also be used to cleanse the crystal.
Source: Practical Psychic Self-Defense for Home and Office by Master Choa Kok Sui.