onyx vs chalcedony

onyx and chalcedony both are nouns.

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

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

onyx: a chalcedony with alternating black and white bands; used in making cameos
chalcedony: a milky or greyish translucent to transparent quartz

Other hypernyms of onyx include calcedony.

onyx (noun)	chalcedony (noun)
a chalcedony with alternating black and white bands; used in making cameos	a milky or greyish translucent to transparent quartz