Quartz

specimen number:
2013621

location:
Keokuk, Iowa, USA

description:
A classic example of what many call a dew drop geode, these with tiny sparkling crystals of quartz throughout the open cavity. A colorless translucent calcite crystal just under 2.0 cm is present as well. This is in terrific condition.

The formation of Keokuk geodes in the tri-state area of Iowa, Missouri, and Illinois is a fascinating geological process centered within the Mississippian-aged Warsaw Formation. Geologically, these geodes began as rounded nodules of anhydro-rock or calcareous concretions within a soft, shaly limestone and dolomite matrix deposited roughly 340 million years ago. Over millions of years, mineral-rich groundwater dissolved the original centers of these nodules, leaving behind hollow voids encased in a durable, waxy chalcedony shell. Secondary minerals, primarily quartz, but also calcite, dolomite, pyrite, and rarely millerite or kaolinite, then precipitated from the percolating fluids to form the internal crystal linings. Historically, while never mined as a primary industrial resource, the Keokuk area has seen continuous quarrying and surface collection since the mid-19th century, with peak activity for scientific and commercial mineral collecting occurring from the 1940s to the present. The region is so significant that the geode was designated the state rock of Iowa in 1967. Today, numerous active quarries and dedicated collecting sites allow enthusiasts to extract these unique geological specimens, which are world-renowned for their variety and the precision of their internal crystal structures.

Questions about this specimen?
Send an email or call us: 314-341-1811.