opal vs fire opal

opal and fire opal both are nouns.

Word	Noun	Adjective	Verb	Adverb
opal	Yes	No	No	No
fire opal	Yes	No	No	No

As nouns, fire opal is a hyponym of opal; that is, fire opal is a word with a more specific, narrower meaning than opal:

opal: a translucent mineral consisting of hydrated silica of variable color; some varieties are used as gemstones
fire opal: an opal with flaming orange and yellow and red colors

Other hyponyms of opal include black opal, girasol, harlequin opal.

opal (noun)	fire opal (noun)
a translucent mineral consisting of hydrated silica of variable color; some varieties are used as gemstones	an opal with flaming orange and yellow and red colors