calcite vs Iceland spar

calcite and Iceland spar both are nouns.

Word	Noun	Adjective	Verb	Adverb
calcite	Yes	No	No	No
Iceland spar	Yes	No	No	No

As nouns, Iceland spar is a hyponym of calcite; that is, Iceland spar is a word with a more specific, narrower meaning than calcite:

calcite: a common mineral consisting of crystallized calcium carbonate; a major constituent of limestone
Iceland spar: a transparent calcite found in Iceland and used in polarizing microscopes

Other hyponyms of calcite include alabaster, Mexican onyx, onyx marble, oriental alabaster, chalk.

calcite (noun)	Iceland spar (noun)
a common mineral consisting of crystallized calcium carbonate; a major constituent of limestone	a transparent calcite found in Iceland and used in polarizing microscopes