You can use any crystal you want to help aid different chakras. Red for root, Orange for Sacral, Yellow for Solar Plexus, Green for Heart, Aquablue for Throat, Indigo blue for Third Eye, and Violet for Crown. If you're having pain in any of these areas, you can place the according crystals (clear quartz can also replace any crystals you may be lacking) over the area and do breathing meditations. There are also different practices for building strength in certain areas, for instance this one is from a book I read on how to access your chakras, on the root chakra (I'm paraphrasing, but if you'd like a direct quote, I'll go ahead and grab the book for anyone who requests):
Find a comfortable, quiet place. Make sure it's warm, perhaps wrap yourself in a blanket or even lay in the sun by a window or outside. Curl into the fetal position, close your eyes, and breathe deeply. Imagine you are in your mother's womb. Try to imagine the sounds, the muffled breathing, maybe even create a small heartbeat with a recording or the beat of a drum. You may put a red blanket or shirt over your eyes in order to fully create the effect. Stay like this for as long as you choose, preferably for at least ten minutes, and try to find the peace, quiet, and trust one feels in the mother's womb. A regular exercise like this can help heal and aid your root chakra and build trust in others and your environment.
