smithsonite

Smithsonite is a zinc carbonate mineral with the chemical formula ZnCO3. It is a secondary mineral that forms in the oxidized zones of zinc ore deposits, typically through the alteration of primary zinc minerals such as sphalerite. Smithsonite can occur wherever zinc-bearing minerals weather and interact with carbonates.

Smithsonite crystallizes in the hexagonal system, but crystals are relatively rare. More commonly, it forms botryoidal, reniform, or stalactitic aggregates. The color range is broad and often striking, including white, gray, blue, green, pink, yellow, and brown, with hues influenced by trace impurities such as copper, cobalt, or manganese. The streak is white, and the hardness is about 4 to 4.5 on the Mohs scale. It is readily scratched by glass and fizzes with dilute acids due to its carbonate composition.

Occurrence and associations: smithsonite is widely distributed in oxidized zinc-rich ore bodies around the world. It is frequently found with other secondary zinc minerals such as cerussite and hydrozincite and can occur alongside minerals like hemimorphite, malachite, or azurite in ore-processing regions.

Etymology and uses: the mineral was named after James Smithson, the founder of the Smithsonian Institution. Historically known as calamine in some localities, smithsonite remains an important zinc ore in places, though it is primarily valued today by collectors for its varied colors and botryoidal forms.