Field Trip to Trowbridge Hall

Trowbridge Hall is home to the University of Iowa’s widely recognized Geoscience Department and the Iowa Geological and Water Survey, yet it also houses a little-known collection that is on display in its very halls. Within this historic building resides a collection of both hard-to-find and familiar minerals from around the state and around the world and whose histories are as varied as their colors and shapes. 

One example is this specimen of selenite found in Oklahoma. Selenite, otherwise known as Gypsum (CaSO₄*₂H₂O), is a common sulfate evaporate mineral found in warm, arid regions. Gypsum is typically clear to white in color but can sometimes come in brown tabular shapes as show in the specimen to the right. Gypsum is also a very soft mineral often used in plaster and cement, but another form, referred to as “alabaster,” is used in stone and monument carving. 

Realgar is an arsenic sulfide mineral (AsS), pictured right, which is only common in certain areas with low-temperature hydrothermal activity. Realgar can appear to be blood-red with prismatic crystals, but once exposed to sunlight and weathering, begins to change to the typical yellow and granular structure associated with sulfur deposits. This substance was once used in early fireworks manufacturing in China to produce the brilliant white colors that are now produced by many powdered metals such as magnesium. Realgar was also used by the ancient Greeks and Romans as a type of rat poison and red pigment in paints. 

 Heulandite is a silicate mineral with a lot going on. The chemical composition contains calcium, sodium, aluminum, silicon, oxygen and water molecules, a large mix of atoms for such small crystals, and is formed in the cavities commonly found in the volcanic rocks called basalts and in lower-temperature hydrothermal settings. These crystals are commonly tabular and radiate out from a single point in a cavity.

The mineral above is an interesting specimen with a long history and a dangerous side. Cinnabar is a mercury sulfide (HgS) with a beautiful red to purple color and a rhombohedral to tabular shape typically crystallizing in areas of lower temperatures around volcanic hot springs alongside opal. As many now know, mercury is a very sever hazard to humans and animals, and cinnabar is a common mineral ore for mercury, yet people in ancient China did not realize this information. In the Taoist tradition, priests would create mixtures with cinnabar to provide to emperors and elite leaders in order to prolong their life; however, we now know that cinnabar has the complete opposite effect, inflicting the imbiber with mercury poisoning.

These minerals mentioned here, and many other illustrious specimens, can be seen on display in the hallways of Trowbridge Hall on the University of Iowa campus. Please contact the Museum of Natural History with any questions about the location or about any of the minerals on display.  

-Written by MNH Education Staff Member Lee Falkena