Crystals are very useful tools in healing and ascension work. In my e-book titled Heal Yourself - Heal the World: Preparing for the New World Consciousness, I mention that I used green aventurine to heal an aura imprint from a past life.
There are many types of crystals and gemstones that can used in the healing and ascension work and the decision as to which ones to use is based on what types of issues and/or blocks an individual needs to work on. For example, Tigers Eye is one of the crystals I am currently working with. This crystal is helping me to better serve my ascension process by enabling me to achieve better mental focus and thought processes and allowing me to be more aware of my conditioned responses and self-imposed limitations.
Your higher inner guidance and intuition can help you to discern which crystals are best for you in the current stage of your healing and ascension work. I also find that when I'm selecting a crystal to purchase, it helps to hold the crystal and see if it "speaks" to me. I've selected many of my most helpful crystals simply by holding them and seeing if they resonated with me. If a crystal feels right then I know it's a crystal that I may need in my healing and ascension work.