Smithsonite is a mineral form of zinc carbonate (ZnCO3). It is a secondary mineral that occurs in the oxidation zone of zinc ore deposits. It is a soft, brittle mineral with a Mohs hardness of 4.5 and a specific gravity of 4.4 to 4.5. Smithsonite is typically found in earthy, botryoidal masses, but it can also be found in stalactites, stalagmites, and other forms. It has a vitreous luster and a white streak.
Smithsonite was first identified as a distinct mineral in 1802 by English chemist and mineralogist James Smithson. It was named for him in 1832 by French mineralogist François Sulpice Beudant.
Smithsonite is a common mineral in the oxidation zone of zinc ore deposits. It is found in association with other secondary zinc minerals such as hemimorphite, hydrozincite, and willemite. It is also found in association with primary zinc minerals such as sphalerite and wurtzite.
There are several varieties of smithsonite, including:
- Cadmiosmithsonite (synonym: cadmian smithsonite): A variety of smithsonite that contains cadmium.
- Cobaltosmithsonite (synonym: cobaltoan smithsonite, cobaltismithsonite, cobalsmithonite): A variety of smithsonite that contains cobalt.
From the San Antonio Mine, Chihuahua, Mexico.|
Credit: The Mineral Gallery, Inc.
The rice grain Smithsonites are satiny lustrous and contrast perfectly with the lustrous, albeit colorless Hemimorphite crystals. They exhibit the absolute BEST color that leans a bit towards the bluish-green side of sea green.