What’s in the Box? Green Eyes

These concentric green circles look like some kind of painting or an old-fashioned LP gone wrong, but in reality this mesmerizing pattern was created by nature. This is the mineral malachite, a copper carbonate associated with ore deposits.

Green malachite "eye"

Malachite forms when other copper minerals like chalcopyrite react with acidic water percolating through the rock. This water can carry copper atoms along for a bit before the copper begins to combine with other atoms and grow minerals like malachite. Sometimes, the water drips into open cavities in the surrounding rock, and malachite will grow as a stalactite or stalagmite the same way other cave formations do.

The photo above shows a slice through a malachite stalactite. The concentric rings come from the growth of the stalactite in fits and starts, and the light and dark colors reflect small changes in the water chemistry over time.

Even though it was made by nature, a little human ingenuity helps this pattern to shine: the rings are most striking in malachite pieces that have been cut and polished like this one.

This post is part of our What’s in the Box? series.

Rice Northwest Museum of Rocks & Minerals
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