agate vs chalcedony

agate and chalcedony both are nouns.

Word	Noun	Adjective	Verb	Adverb
agate	Yes	No	No	No
chalcedony	Yes	No	No	No

As nouns, chalcedony is a hypernym of agate; that is, chalcedony is a word with a broader meaning than agate:

agate: an impure form of quartz consisting of banded chalcedony; used as a gemstone and for making mortars and pestles
chalcedony: a milky or greyish translucent to transparent quartz

Other hypernyms of agate include calcedony.

agate (noun)	chalcedony (noun)
an impure form of quartz consisting of banded chalcedony; used as a gemstone and for making mortars and pestles	a milky or greyish translucent to transparent quartz