Prehnite is considered a "stone of dreaming". It is believed to increase the power of the dream state, strengthen lucid dreaming and promote communication with other planes of existence. Prehnite alleviates nightmares, phobias and deep fears, uncovering and healing the disease that creates them. It is a stone for dreaming and remembering.
Amethyst is by far one of the most widely used and known crystals for sleep. It provides both a soothing and serene frequency that will calm your surroundings making you feel very relaxed in its presence.