Smithsoniet

Smithsonite is a zinc carbonate mineral with the chemical formula ZnCO3. It is named after James Smithson, the founder of the Smithsonian Institution in Washington, D.C., who conducted extensive research on this mineral. Smithsonite is a secondary mineral, meaning it forms through the weathering and alteration of primary zinc minerals like sphalerite. It is often found in the oxidized zones of zinc deposits, associated with other secondary minerals such as hemimorphite, cerussite, and limonite.

The color of smithsonite can vary widely, ranging from colorless and white to yellow, brown, pink, green, blue, and gray. This variability in color is often due to impurities within the crystal structure, such as iron, cadmium, or manganese. Smithsonite typically occurs in botryoidal, reniform, or stalactitic masses, though well-formed crystals are rare. It has a relatively low hardness, rating 4 to 4.5 on the Mohs scale, and a specific gravity of around 4.4 to 4.5. It is typically found in hydrothermal veins and sedimentary rock environments.

While smithsonite is not a primary ore of zinc due to its often small and scattered occurrences, it can be an important secondary ore when found in sufficient quantities. It has also been used as a minor gemstone, particularly in its more attractive colored varieties. The mineral's type locality is in the Rosas Mine, Sardinia, Italy.