precious stone vs gem

precious stone and gem both are nouns.

Word	Noun	Adjective	Verb	Adverb
precious stone	Yes	No	No	No
gem	Yes	No	No	No

As nouns, precious stone and gem are synonyms defined as:

precious stone and gem: a precious or semiprecious stone incorporated into a piece of jewelry

Other synonyms of precious stone include jewel.

precious stone (noun)	gem (noun)
a precious or semiprecious stone incorporated into a piece of jewelry	a precious or semiprecious stone incorporated into a piece of jewelry
	art highly prized for its beauty or perfection
	a sweet quick bread baked in a cup-shaped pan
	a person who is as brilliant and precious as a piece of jewelry
	a crystalline rock that can be cut and polished for jewelry