University of Montevallo hides forgotten rock

Published 12:00 am Wednesday, November 15, 2006


Millions of years ago, slushy water seeping through swamps in Shelby County left a deposit of iron oxide, which when found in the late 1960s was a giant, round, hollow formation dubbed &8220;the largest known geode in the world.&8221;

The eight-ton geode is displayed in an atrium at the University of Montevallo, surrounded by the school&8217;s Harman Hall, home of the department of biology, chemistry and mathematics. The late Dr. J. F. L. Connell, a geology professor known to his students as &8220;Dr. Rock,&8221; often told visitors that the facility was built around the giant geode in 1970. Today, sightseers often mistake the oddity for a meteorite, but a plaque mounted on the front of the geode’s pedestal leaves little doubt about the origin of the mammoth formation.

It is composed of iron-oxide minerals, primarily hematite, goethite and limonite. The geode was formed when ground water, seeping through cracks and pore spaces in surrounding rock, dissolved a cavity in the rock of which the geode became a part. Ground water, heavily charged with dissolved iron, seeped along the cavity walls, evaporating and leaving behind the gummy iron residue which slowly hardened to form the various structures inside the mouth of the geode.

Stalactites, ropy patterns and grape-like lumps are visible by peering into the three-foot mouth of the geode. Iridescent colors of black, purple, blue, red and green add interest to the attraction.

Barbara Brande, assistant professor of geology at Montevallo, said kidney-shaped, bulbous formations of hematite inside the geode look like &8220;shiny multi-colored bubbles.&8221;

The colors represent minute amounts of sulphur, copper and various minerals contained in the original solution.

Brande said it isn&8217;t unusual for cavities to form in limestone-rich area of Shelby County. &8220;Iron-rich ground water enters the cavity and deposits a variety of iron minerals. Concentric layers (represented by rings) are formed, and this accounts for the color variations inside the geode. The saying goes, &8216;what ground water takes away, ground water puts back.&8217;&8221;

Cynthia K. Shackelford, director of public relations at Montevallo, said the geode has been included in a number of walking tours directed by the university and the community. The site also is a popular stop-over for Boy Scout groups and others studying rock formations. Brande said area school groups visiting Harman Hall are usually taken to the atrium for a geode show-and-tell session.

Geology aficionado Dr. Mark Manning of the University of Colorado at Denver, told about the geode during a campus visit, proclaimed the &8220;world&8217;s largest known geode&8221; a remarkable product of the processes of nature. He said he hopes to study it further during a subsequent visit to Montevallo.

The geode was extracted from an iron quarry in northwest Shelby County in November 1965. It was donated to the university by Shook and Fletcher Mining Co. and the Shelby County Highway Department