\Mar"ca*site\, n. [F. marcassite; cf. It. marcassita, Sp. marquesita, Pg. marquezita; all fr. Ar. marqash[=i]tha.] (Min.) A sulphide of iron resembling pyrite or common iron pyrites in composition, but differing in form; white iron pyrites. {Golden marcasite}, tin. [Obs.]