Put all the ingredients except for the carnelian gemstone in a bowl and mix with a wooden spoon.
Add the carnelian gemstone to the mixture to infuse into the salt.
Store the mixture in a glass jar with a lid and label.
To use your bath soak, draw a warm bath, placing a handful of the mixture into the water to dissolve, leaving the gemstone in the jar. Soak for 20 minutes. Keep in mind that pigmented clays can stain white towels, robes, and rugs, so plan accordingly.
Gently pat your skin dry.