A purple stone on a mood ring indicates that the wearer is in a particularly happy or romantic mood. A purple mood ring color is associated with love and passion.
A mood ring's stone is really a glass shell or a hollow piece of quartz that contains thermotropic liquid crystals or a strip of liquid crystals under a protective coating. As the temperature of the adjacent skin changes, the crystals twist and alter the wavelengths of light that the crystals reflect or absorb. At a standard temperature of 82 degrees Fahrenheit, the ring is blue or green. As the temperature increases, the ring turns purple.