These geodes occur in Lime Creek shales. They are rather unusual in containing a number of roundish cavities rather than the customary rough opening. The cavities are lined with: 1. small rhombic calcite crystals which are bronzed with limonite; 2. occasional tabular and fan-shaped aggregates of barite crystals. The mode of formation is obscure.
Proceedings of the Iowa Academy of Science
©1922 Iowa Academy of Science, Inc.
Galpin, S. L.
"The Rockford Geodes,"
Proceedings of the Iowa Academy of Science, 29(1), 128-129.
Available at: https://scholarworks.uni.edu/pias/vol29/iss1/25