The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.
Malachite is abundant in its typical forms, so even the best specimens are modestly priced. Pieces showing an unusual crystal habit, distinctive pattern, or chatoyancy will have higher values. Rocks consisting of malachite and other colorful copper minerals in lovely combinations generally command higher prices than pure malachites. The value of carvings and ornamental objects hinges primarily on the size and artistry of the work.