Na₂Cu(SO₄)₂ .2H₂O

This sample of Krohnkite is displayed in the Smithsonian Museum of Natural History. Krohnkite is a sulfate of copper and sodium with the composition Na₂Cu(SO₄)₂.2H₂O. The sample at left is about 12x12 cm and is from Chuquicamata, Atacama, Chile.