noun
: any of various silicates of magnesium: as
a. : a tetrasilicate Mg 3 Si 4 O 10 (OH) 2 found in nature as talc from which it is obtained usually in fibrous or micaceous forms for use chiefly as a filler or extender (as in paints)
b. : a trisilicate approximately Mg 2 Si 3 O 8 . n H 2 O obtained by precipitation as a white powder and used chiefly in medicine as a gastric antacid adsorbent and coating (as in the treatment of ulcers)