Smithsonite, also known as turkey fat or zinc spar, is zinc carbonate (Zn 3), a mineral ore of zinc. Historically, smithsonite was identified with hemimorphite before it was realized that they were two different minerals. The two minerals are very similar in appearance and the term calamine has been used for both, leading to some confusion. The distinct mineral smithsonite was named in 1832 by François Sulpice Beudant in honor of English James Smithson (c.1765–1829), whose bequest established the Smithsonian Institution and who first identified the mineral in 1802.
Smithsonite is a variably colored trigonal mineral which only rarely is found in well formed crystals. The typical habit is as earthy botryoidal of 4.5 and a specific gravity of 4.4 to 4.5.
Smithsonite occurs as a secondary mineral in the weathering or oxidation deposits. It sometimes occurs as replacement bodies in carbonate rocks and as such may constitute zinc ore. It commonly occurs in association with hemimorphite, willemite , malachite and anglesite series, with substitution of manganese leading to rhodochrosite