New Mexico Mineral Symposium — Abstracts

The midwestern states of Ohio, Indiana, Kentucky, Tennessee, Illinois, and Missouri share a simple suite of minerals that are found wherever dolomitized limestones crop out or are exposed by surface or underground mining. Of interest to collectors are approximately two dozen minerals that can occur as well-crystallized carbonates, sulfides, sulfates, oxides, or halides composed of eleven metals and silicon. The following table lists these minerals and the elements that form them. 

Metals present in the original sediments were mobilized by relatively low-temperature (100-200°C) fluids flowing upslope from the ancient basins and saline seas of the region and were concentrated. As these fluids reached an arch or a dome adjacent to the basins, minerals crystallized in open cavities within the host rock when the pressure and temperature were reduced. Other factors, such as the pH of the fluid, the presence of pyrobitumen, and the presence of fresh formation water influenced the timing and degree of crystallization.

Minerals found in the limestones of the Midwest are often well crystallized, beautiful, and abundant and occur in a wide range of habit, color, and association with other minerals.