opal vs harlequin opal

opal and harlequin opal both are nouns.

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

As nouns, harlequin opal is a hyponym of opal; that is, harlequin 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
harlequin opal: a reddish opal with small patches of brilliant color

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

opal (noun)	harlequin opal (noun)
a translucent mineral consisting of hydrated silica of variable color; some varieties are used as gemstones	a reddish opal with small patches of brilliant color