Smoky quartz's spiritual meaning is centered on grounding, protection, and the transmutation of negative energy into positive energy. It is associated with the root chakra and is believed to provide a sense of stability, strength, and security while helping to release fear, stress, and other unwanted vibrations. Historically, it has been used as a talisman for protection against negative forces. 
Smoky quartz is associated with the zodiac signs of Scorpio, Sagittarius, Capricorn, and Aquarius. It is considered a grounding and protective stone, beneficial for Scorpio, Sagittarius, and Capricorn by providing stability and cleansing energy. For Aquarius, it is thought to help ground their often idealistic nature. It is also sometimes mentioned as a birthstone for Libra or June.