COLUMN: Iowa's state rock

     Looking out my window at the patchy snow, ice, and brown winter landscape, my mind drifted back to last spring and one fun and educational day of hunting for Iowa’s state rock. Maybe it’s the abnormally mild mid-winter temperatures tempting my mind with thoughts of spring to come. Or maybe it’s the melting ice that reminded me of last March when I traversed a frigid stream in search of Iowa’s state rock – the geode.

     The geode was designated as Iowa’s official state rock by the Iowa General Assembly in 1967. It was picked over the more plentiful limestone and abundant fossil coral found across the state. Aiding to the appeal of the geode was the large number of rare and beautiful geodes found in parts of the state and the draw to state tourism they create.

     The word “geode” is of Greek origin and means earth-like. This is a good description of their oddly round and lumpy appearance often referred to as resembling a cauliflower. The modern definition of geode is a stone with a hollow space inside lined with crystals or mineral matter.

     In Iowa, geodes are typically two to six inches in diameter but some have been found up to 30 inches around. The most highly prized geodes have hollow interiors, although many geodes are solid. You can sometimes tell if the geode you have found is hollow or solid by its weight and by shaking it to listen for loose crystals and sand within the hollow cavity.

     According to the Iowa Geological Survey, Iowa geodes can contain up to 20 different minerals within, contributing to the color and rarity of each individual specimen. Quartz is the most common mineral with beautiful transparent to white quartz crystals covering the walls of many geode cavities.

     In many geodes, chalcedony layers cover the previously generated quartz crystals generating colors ranging from white, gray, blue, and yellow to orange. Calcite is another common mineral in many Iowa geodes, leading to a wide variety of other crystal formations ranging from clear, white, and amber to brown. A few highly sought-after geodes include those with pyrite or fool’s gold, iron sulfide, sphalerite, and blackish zinc sulfide minerals within.

     Geologists attribute the crystal growth to the percolation of groundwater through the geode walls over millions of years since the time when Iowa was a shallow sea. Geode State Park, located in Henry County in Southeastern Iowa, is named for the occurrence of geodes. Although not abundant in East Central Iowa, there are pockets of geodes here and there.

     Geodes are commonly found in stream beds where they have weathered out of exposed limestone and accumulated downstream. It is important to remember to ask permission from landowners before collecting – most geode rich areas are on private lands. Collecting rocks and artifacts is illegal in many Iowa State Parks and County Conservation Areas.

     If you are lucky enough to find a geode, use an old towel to cover your geode, put on a pair of safety glasses and gloves, and use a rock hammer to deliver a few sharp blows to expose the prize inside. Remember – not all geodes will be hollow. Caution: crystals from your geode can be extremely sharp.