noun
: a carbonate of magnesium: as
a. : the very white crystalline normal salt MgCO 3 that occurs naturally as magnesite and also in the form of dolomite, is prepared artificially by precipitation usually as the trihydrate MgCO 3 .3H 2 O, and is used chiefly in paint and printing ink, as a filler (as in paper and rubber), as an addition to table salt to prevent caking, and in medicine and pharmacy
b. : a crystalline hydrated basic salt obtained by precipitation (as by heating a solution or suspension of the trihydrate) and used in thermal insulation and for many of the same purposes as normal salt