A crystal is a material with a clear, uniform structure.
A psychic deals with the essence of things. Most of the time, the essence we are looking for is buried deeply, hidden from our sights. Crystalline structure is important for psychics because with crystals the essence is clearly visible - the whole form and structure of the crystal is the essence of it.
A crystal for a psychic is a something like a tuning fork for a piano tuner. A tuning fork gives a clear, distinct sound by which we can align the clarity of our hearing. Similarly, a crystal gives of a clear, distinct psychic vibration and energy by which we can align our understanding and experience of the flow of the psychic world around us.
If you let your psychic energy flow through a crystal, you can achieve different effects. Just by touch and feel (or mental imagination) you can observe the vibrational effect of specific kinds of psychic energies.
It can even be beneficial to apply some attributes of crystalline structure (especially the deep, essential clarity) to our own minds, hearts, and physical bodies.
In older ages, a mystic versed in herbalism used herbs in two different ways: for their biochemical effect and for their homeopathic, psychic effect.
The biochemical side of using herbs improved and went on to become modern medicine. Unfortunately, the psychic side of using herbs hasn't improved much - maybe even declined.
How does a psychic herbalist use herbs?
First, the vast knowledge of herbs forms a psychic system - not unlike astrology. Such knowledge provides a framework for understanding mental and psychic processes.
Secondly, herbs can be used in a similar way as crystals. A crystal is a visible, material essence of a type of psychic energy. A psychic can use plants and herbs as tuning forks for psychic energies on the biological level. Understanding this way of using herbs to influence the flow of psychic energies results in the homeopathic effect when used for healing.