Some of the coolest rock on campus, from a geo-nerd point of view, are the facing stones in the main (East) entrance to Haring. Here you will find a presumably accidental juxtaposition of two different facing stones, one being an interesting and somewhat unusual limestone sedimentary rock (beige), the other a metamorphic rock (greenish). Here’s the exciting geo-nerd part...the metamorphic rock formed from a limestone that must have been nearly identical to the other rock. It’s the metasomatized equivalent of the limestone!

Geology word of the day:
Metasomatism – the process in which the chemical composition of a rock is changed. (Geologists like to use the occasional geo-nerd word to impress non-geologists.)

Want some more details? Hang onto your hats...here we go!
When you walk into the entrance of Haring Hall, you immediately see that the walls are covered with two different types of polished rock. One rock is a beige colored, layered sedimentary rock composed of the calcium carbonate that we call limestone. The nature of the layers in the limestone tell us that it formed in a very shallow lagoonal setting, probably behind a limestone reef. The lack of fossils in the sediment suggest it may have formed in a hot climate with a lagoon that was so salty due to evaporation of seawater that the only things that could live there were algae and bacteria. It was apparently too salty for clams and snails and other creatures that could have left fossil shells. The abundant open spaces and cavities filled with fine-grained sediment formed when rotting algae and bacteria fermented - releasing gases that made gas pockets which were preserved because the calcium carbonate sediment forming the rock was being cemented together by carbonate crystals formed in response to the evaporation. This is some of the evidence that tells us the rock formed in a shallow water lagoon.

The other rock has thin layers and a texture that looks a lot like the limestone, but rather than being composed of soft calcium carbonate, this rock is made of hard minerals that are various shades of greens, browns and whites. The minerals in this rock are diopside, epidote, vesuvianite, and quartz. These are minerals that occur in high temperature metamorphic rocks called skarns that form when granite magmas intrude into buried limestone at great depths. The high temperatures cause the rock to recrystallize and change form (or metamorphose) from a sedimentary rock to a metamorphic rock. When the granite magma cools and crystallizes, it releases high temperature fluids that carry dissolved elements like silicon and aluminum, that flow through the limestone and cause the calcium carbonate to be replaced by various calcium silicate and calcium aluminum silicate minerals, changing the chemical composition of the rock in a process geologists call metasomatism (all together now..."Metasomatism is the process in which the chemical composition of a rock is changed." Very good; you've been paying attention to your tour guide).

The textures in the green metamorphic rocks match the textures in the buff colored limestone and suggest that the metamorphic rock formed due to heating and chemical alteration of a shallow water limestone. The shallow water lagoonal limestone is not a very common type of limestone. It is surprising to see that the building architect paired this unusual limestone with a high temperature metamorphic rock that must have also formed from a very similar limestone. Was this just an accident? Was the architect really just a frustrated geologist? Was the architect a truly sensitive artist in touch with mother earth who instinctively knew these two rocks belonged together? The folks in the Geology Department would love to find the answers to those questions, as well as finding out where these two different rocks were quarried if any knows who the architect was.

Okay, on to the next stop on the tour. Oops! We almost forgot; before we leave, let's check the steps on both the S&E sides of Haring for fossils. Everybody gather around closely...

This is most likely “Indiana limestone” which is extensively used as an architectural detail or a facing stone. The limestone is almost exclusively composed of CaCO3 skeletal fragments, and is Mississippian in age (Late Paleozoic). The limestone was formed at a time when central Indiana was below sea level, and was shallow enough to have a carbonate bank formed on it. Sediment from land couldn’t reach the area, so the limestone is very “pure.” Because of the shallow water environment in which this limestone formed, all of the finer material (smaller than sand-sized) has been washed away as the rock was forming - that is, as the animals that produced the CaCO3 skeletons were growing and dying - leaving only sand-sized or larger particles. As a result, this limestone has many features commonly associated with sandstones: ripple marks, sand waves, and cross bedding. The most common fossils (skeletons) in this rock are bryozoans - filter-feeding colonial animals that resemble corals, but are actually related to brachiopods, and crinoids - commonly known as sea-lillies, which are echinoderms. Echinoderms, meaning spiny skin, include starfish, sea urchins, brittle stars, and sea cucumbers. Other fossils that you can find in this rock are rugose corals, commonly known as horn corals, and brachiopods, which look kind of like clams, but are very different inside.