Among all energetic and chakra stones available, I would recommend Amethyst as the best gemstone for meditation. Its properties are among the best crystals to enhance meditation and to help someone enter into the meditative state easier. It is known as the "Stone of Spirituality". Amethyst is also a protective crystal. Kyanite would also be a nice choice. It has a strong connection to your higher self as well as spirit guides. Kyanite assists in balancing all of the chakras. One other crystal that is highly recommended, more for the aura protective aspect, is Labradorite. Use your intuition to see which one feels right to you for these purposes.