Each crystal has its own energetic codes that are an expression of light through color and vibration. They are known for their beauty and hold the energy of Mother Earth. They serve as releasers and activators of energy. Crystals can be placed directly on the body to work with corresponding chakras, arranged as grids on or around the body, or used as accents in the environment to regulate and harmonize energy in the space.
Choose the crystals that are the best match for your soul signature and the intention you have for their use. Use your clairsentience or gut feelings, sense of kinesthetic touch or your third eye for clairvoyant selection of crystals for your intended purpose. Crystals may also be used to make liquid essences for internal use. I like the gem and crystal essences from AlaskanEssences.com.
Animals are highly attuned to energy and the nature kingdom and when given a choice, they often select the stones that are a match for them.
Love is in the Earth by Melody is one of the best comprehensive crystal reference books.