Copper Ore Bookends. Basalt (lava rock) with Copper. This set is app. 9 1/2"W x 6 1/4"H x 1 3/4"D. Our natural rock bookends are cut to show the best pattern, color and veining of each mineral. Float copper bookends are buffed polished and coated to enhance the beauty of the piece. One of a Kind Item. Michigan Native Copper Michigan's Keweenaw Peninsula is the most important locality in the world for pure native copper. Mining began in 1845 and continued until 1968 and over 5 million tons of refined copper were recovered from Michigan's copper mines. In the early 1900's it led the world in copper production and "Lake Copper" was the purity standard to which other refined copper was compared. Long before the mining operations of the past century began in the Keweenaw, pre-historic peoples mined copper from the mineral rich veins.