Pietre dure is the art of using the natural variegation in semi-precious stones to assemble an image—much like a paint-by-number picture, executed as a jigsaw puzzle of stone veneers. Tucked amid the tourist circuit in Florence, the Opificio Delle Pietre Dure (which literally translates to "workshop of semi-precious stones") is the Italian Ministry for Cultural Heritage's center for this intricate art.
The center contains a conservation school, a specialist library, archives of conservations, and a scientific laboratory. But the general public will likely mainly be interested in the museum's display of historic examples of pietre dure, which includes exquisite examples of finished objects—largely tabletops and cabinet plaques, but also an absolutely massive malachite fireplace.
Also on display are samples demonstrating how the stone is cut and fitted together, historical tools once used for the stone work, and extensive displays showcasing the wide varieties of colors and patternings in stone traditionally available to the historical pietra dure craftsperson. The museum is close to the central Florentine tourist crush but is generally sparsely attended—don't be surprised if the ticket seller seems taken aback to see you.