Each crystal is believed to have a different energetic profile, and so certain ones lend themselves best to the treatment of specific issues and chakras. In the case of the sacral chakra, which crystals to use would depend on whether you feel this chakra is blocked (stagnant energy) or overactive (via Chakras Info). In the event your sacral chakra is blocked, both citrine and orange calcite have cleansing properties that could help, while coral calcite also has amplifying qualities, making it a good choice to strengthen the effects of another stone or to heal at a distance. Orange carnelian, because of its color and properties, also help to support healthy creative energy flow.
If, however, you feel that this chakra is overactive, hyper-excited, and resulting in impulsivity or burning yourself out, purple gemstones like amethyst, quartz, and tourmaline can act as a cooling, soothing force to help calm the energy and bring it back into balance. Snowflake obsidian is also useful for bringing balance back into a body dealing with some equilibrium issues.
If you are unsure which direction to go into, it might be worth discussing with an experienced practitioner or healer who has studied these energies and philisophies in depth and can help you assess your needs.