Theft coverage for jewelry is included on most homeowners and renters insurance policies. However, the coverage included on an unendorsed homeowners or renters insurance policy can be very limited. If you want to coverage a piece of jewelry for it’s true value than you need to do one of two things: Specifically schedule the piece of jewelry onto your homeowners or renter insurance policy.
Buy a separate personal articles insurance policy for that piece of jewelry.
In both cases you will need to get the jewelry appraised and give the appraisal to your insurance professional.