pietra dura

from The Century Dictionary.

• Ornamental work in inlay of hard stones, such as agates and jaspers, especially when on a somewhat large scale.

from the GNU version of the Collaborative International Dictionary of English.

• (Fine Arts) Hard and fine stones in general, such as are used for inlay and the like, as distinguished from the softer stones used in building; thus, a Florentine mosaic is a familiar instance of work in pietra dura, though the ground may be soft marble.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun art Hard and fine stones in general, as used for inlay etc. and distinguished from the softer stones used in building.