One of the mineral forms of Copper is malachite. Its chemical composition is Cu2(CO3)(OH)2.The sample shown here at right is about 30 cm tall. It is shown on display at the Smithsonian Museum of Natural History along with another copper containing mineral, cuprite.
This is a closeup of the sample above showing the details of the remarkable columnar structure.
This sample of malachite has a distinctly different appearance. It's horizontal dimension is about 25 cm.