MINERAL OF THE MONTH: June 2016 – Lake Superior Copper Replacement Agates

This web page update features the copper replacement agate. They can only be found in the Keweenaw Peninsula, located in Michigan’s Upper Peninsula. They can be found in the mine dumps near abandoned copper mines from the Kearsarge Lode. Most of these agates are small – less than an inch in diameter. They are extremely rare and difficult to find, usually requiring labor intensive work to free them from the basalt matrix rock. These agates are well sought after because of their rarity, their interesting patterns, and the vast array of other mineral inclusions. In addition to copper these agates often have other mineral inclusions including silver, calcite, malachite, tenorite, epidote, and pumpellyite, In most cases these small agates are fully husked, requiring them to be cut to expose their inner beauty.

The copper replacement agate shown below includes malachite, pumpellyite, and epidote inclusions.

The agate below has white chalcedony bands on the left and clear calcite on the right. Copper is in the outer shell, surrounding the specimen. The green is epidote and the red is a copper oxide.

The two photos below show copper replacement agate nodules in basalt matrix rock. In addition to copper there is also prehnite, epidote, and pumpellyite (dark green inclusions). These photos were taken by Dave Schuder.

The specimen shown below has basaltic matrix on the left and copper replacement on the right. The copper bands alternate with the chalcedony bands. This photo is from my agate book, Agates Inside Out.

CITATION: The first three photos shown above (used with permission) are from the Wayne W. Sukow collection http://www.sukowssuperiorminerals.com.

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