Quite literally Lapidary is the art of cutting and polishing stone. The implication is that the stone is decorative and rare and is, therefore, precious.
The person who cuts and polishes such a stone is also called a Lapidary. This is somewhat different to a Stonemason who fashions large pieces of rock into items that are more often functional rather than being purely decorative.
Gravestones, for example, are cut and polished by “Monunmental” Stone Masons even though their work is often highly decorative.