This has been a banner year in the world of geology for Illinois. One of the biggest and most notable breakthroughs is the recent organized efforts to establish a new state symbol—the state rock— thanks to the students at a local middle school. The campaign originated in a fifth-grade classroom at Pleasantdale Middle School in Burr Ridge, where students selected three rocks found in the state and created a website allowing visitors to vote on their choice, culminating in a fierce and “rocky” competition with input from geology scholars, student peers, and public voices alike, including our very own educator, Sara Kurth. Ultimately, the specimen chosen was dolostone. The other two rocks up for candidacy were limestone and sandstone, which can also be found across Illinois.

According to our geologist Sara Kurth, ‘dolostone was formed during the Ordovician era (450 million years ago) in the warm seas that covered much of the earth. While similar to limestone, dolostone is composed of at least 50% dolomite, a calcium carbonate with added magnesium, CaMg(CO₃)₂. Limestone is primarily made of calcite, CaCO₃. There is still debate among geologists as to what causes the dolomite to replace the calcite in limestone, although one of the leading arguments suggests that high rates of evaporation of sea water results in raising the calcium to magnesium ratio in the leftover brine. From that brine, dolomite would form and the process of lithification results in the formation of dolostone. Because of their similarities, it is difficult to definitively distinguish dolostone and limestone, although dolostone tends to be harder and more resistant to acids compared to limestone.’  

Dolostone is part of the very bedrock here in Illinois, and additionally has many architectural and industrial uses. Quarried dolostone is used as a building material, mixed in concrete and used in gravel driveways or paths. The mineral dolomite is used in medicines to treat osteoporosis and hypothyroidism. As a Pleasantdale graduate, I feel such pride in knowing that this upcoming state symbol has its origins from my very alma mater!  It is highly inspiring to see such young individuals interested in the field of geology and be able to see their work come to fruition. Thanks to the combined efforts of these students, Illinois is the 29^th state to declare a state rock.

In addition to admiring dolostone and its recent fame, you can enjoy seeing it for yourself through expeditions of your own! Illinois is renowned for its natural repositories of dolostone, spanning the entire state. A sedimentary rock, this is very common in quarries and dolomite prairies, which can be found across several northern counties. A few of these prairies include the Colored Sands Bluff Nature Preserve in Winnebago County, the Lockport Prairie Nature Preserve in Will County, and the Jarrett Prairie Nature Preserve in Ogle County. For more information on Illinois Dolostone Prairies visit the webpage of the Illinois Department of Natural Resources.

As luck would have it the Lizzadro Museum is planning a collecting field trip to a dolostone quarry! Saturday, July 16, is our Fossil Collecting Trip to Irene Quarry in Belvidere, Illinois to collect marine fossils. These dolomitic limestone rocks contain fossils including brachiopods, cephalopods, corals, crinoids, gastropods, and more. Sign up for the field trip here!

Marguerite Striegel is interning at the Museum this summer. She is currently a junior attending Boston College and studying Art History with a concentration in Museum Studies. She is the executive writer of the Boston College Arts Journal and a Student Ambassador at the McMullen Museum of Arts on campus. She hopes to further her knowledge of museum work at the museum this summer and pursue a career in the curatorial field.