Iowa Gems and Minerals in Your Pocket Format: Other (Undefined)

Most, if not all, of Iowa’s gems and minerals are products of crystallization in underground cavities that filled with water containing dissolved chemicals. The famed Iowa geodes (Iowa’s state rock) are products of a complex process of replacement and cavity-filling in the Warsaw Shale. Armored by a rind of tough chalcedonic quartz, these spheroidal masses, which range up to more than a meter across, weather out of the host rock and accumulate along streams in the southeastern part of the state. During the Pleistocene Epoch, large masses of glacial ice rafted the ultra-fine-grained variety of quartz called Lake Superior agates, which had previously weathered out of their host rocks, southward into Iowa. They can be found in the gravels that have accumulated along major streams in the eastern half of the state.

Iowa’s long record of mining lead, coal, gypsum, and limestone contains a rich history; the forty-seven mineral specimens inIowa Gems and Minerals in Your Pocketmake up a fascinating illustrated guide to that history. Carefully lit and photographed to reveal both maximum detail and maximum beauty, each specimen becomes a work of art.

Paul Garvin is professor emeritus of geology at Cornell College and the author of Iowa’s Minerals: Their Occurrence, Origins, Industries, and Lore (Iowa, 1998). Anthony Plaut is a professor of art at Cornell College.