WordNet records no synonym and no antonym for magnesium carbonate. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a very white crystalline salt that occurs naturally as magnesite or as dolomite
Synonyms, antonyms and the broader and narrower relations for magnesium carbonate come from Princeton University’s WordNet. Full sources and licences.