Hardness and Toughness
Gem and mineral hardness is measured on the Mohs scale. The numbers are based on the relative ease or difficulty with which one mineral can be scratched by another. But the Mohs scale is deceptive. The steps between the minerals are not evenly spaced. For example, diamond is only one number away, but it’s many times harder than gems in the corundum family.
Feldspars, including sunstone, share two traits that affect their durability and make them vulnerable to damage. These are softness—at 6.5 to 7.2 on the Mohs scale—and cleavage in two directions, which gives sunstone a Poor toughness rating.
When sunstone is mounted in a setting that protects it, however, it’s an excellent choice for jewelry. Protective settings include pendants, earrings, and pins rather than rings, which are more likely to receive knocks and bumps.
Exposure to heat is not recommended for sunstone, but its color is stable when exposed to light and won’t fade.
Warm, soapy water is always a safe sunstone cleaning method. Ultrasonic and steam cleaners should be avoided. Feldspars are rapidly attacked by hydrochloric acid, so cleaning products containing bleach should also be avoided.
Rarely, sunstone might be fracture filled. These stones should only be cleaned with warm, soapy water.