Smithsonite, or zinc spar, is zinc carbonate (ZnCO3), a mineral ore of zinc. Historically, smithsonite was identified with hemimorphite before it was realised that they were two distinct 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 chemist and mineralogist 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 masses. It has a Mohs hardness of 4.5 and a specific gravity of 4.4 to 4.5.
Smithsonite occurs as a secondary mineral in the weathering or oxidation zone of zinc-bearing ore 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, hydrozincite, cerussite, malachite, azurite, aurichalcite and anglesite. It forms two limited solid solution series, with substitution of manganese leading to rhodochrosite, and with iron, leading to siderite.
Smithsonite is a secondary mineral of the oxidized zones of zinc ores. It is relatively rare as a mineral and even rarer as a cabochon or faceted gem. The best deposits of Smithsonites are in Mexico (green, blue, pink), in the state of New Mexico in the USA (blue, green), in Sardinia (yellow), in Greece (blue, green) Namibia (green, pink, colorless, beige, yellow), Morocco (green, yellow) and Australia (colorless, green).
The Smithsonite is usually translucent, rarely transparent. The mineral occurs in thin crust, nipples, hemispheres or prismatic single crystals. The aggregate may have a fibroradic structure sometimes visible to the naked eye, except under the microscope or microscope. The pastel colors of the Smithsonite are very attractive. Blue and green are caused by impurities of copper, pink by cobalt and bright yellow by cadmium.
The rather fragile and is therefore aimed at collectors rather than jewelers, although splendid green, yellow, pink and blue specimens have already been seen mounted in earrings and pendant. A special feature of this stone is its high density (4,35-4,48), well above the average of other better known gems such as Quartz (2,50-2,90) or Beryl (2,65 -2.92).