hardstone 
noun [mass noun]
Precious or semi-precious stone used for intaglio, mosaic work, etc.Since the art of cameo cutting is such a difficult one, these hardstone royal images were regarded as the most prestigious of gifts, reserved either for a close relation of the monarch or a person of the greatest political importance....
- Scagliola, an ancient Roman technique revived in the renaissance, is in essence the imitation of marble or hardstone with a powdered crystalline version of gypsum, which is mixed with glue, coloured and polished.
- Prague once again became a great centre of hardstone - not to mention rock crystal - production in the later sixteenth century by virtue of the patronage of Emperor Rudolph II.