Valuable Items Insurance
A valuable items policy, or "Personal Articles Floater", insures collectible and appraisable items in case of loss, theft or damage. Items such as jewelry, artwork, fine china, collectible firearms, and anything else that requires an appraisal in order to establish a value for replacement need to be insured separately from your homeowner's policy or scheduled directly on it.
It is also possible to purchase a "blanket" on a homeowner's policy to cover items without specifically scheduling them. This can be of great use when you have a number of smaller pieces that need coverage.
Many homeowner's policies provide some form of limited protection for collectibles on a blanket basis for theft, but not necessarily for mysterious disappearance – this protection tends to vary by insurer and policy.
Check with your agent to make sure you are covered properly.