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.
Lapis is between 5 and 6 on the Mohs scale, depending on its composition. With care, lapis jewelry and carvings can delight their owners for generations. Its toughness is considered Fair.
The dye used in some lapis can come off if it’s rubbed with acetone (nail polish remover) or denatured alcohol, so it’s sometimes sealed with wax or plastic. Wax sealers can deteriorate when they’re exposed to heat or solvents.
Lapis that hasn’t been dyed might be impregnated with wax or oil to improve its color and luster. These treatments have only fair stability, and a gemologist can detect them.
Warm, soapy water is the safest way to clean lapis lazuli. It’s best to test a small, inconspicuous area first, because some dye treatments are not stable.