gemstone vs gem

gemstone and gem both are nouns.

Word	Noun	Adjective	Verb	Adverb
gemstone	Yes	No	No	No
gem	Yes	No	No	No

As nouns, gemstone and gem are synonyms defined as:

gemstone and gem: a crystalline rock that can be cut and polished for jewelry

Other synonyms of gemstone include stone.

gemstone (noun)	gem (noun)
a crystalline rock that can be cut and polished for 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