As our trees are dropping their leaves and the landscape is feeling more bare by the day, there’s a different natural feature whose mark is more visible on our landscape. While overshadowed by towering oaks and dense greenery in the spring and summer months, or blanketed in snow through the winter, Wisconsin red granite, our state rock, stands out in the grays and browns of November. But what exactly is granite and what gives Wisconsin red granite its namesake shade? It’s helpful to break down red granite into its composite parts–red and granite. 

What is Granite?

Granite is an intrusive igneous rock, meaning it was formed when molten rock, or magma, cooled below the surface to form solid rock. This slow cooling process allows more time for large structures in the rock to grow, giving granite its coarser grain and more crystalline features. Extrusive igneous rocks, unlike granite, are formed when molten rock exits the Earth rapidly, also known as volcanic eruptions, and doesn’t have time to form those crystals. This fast cooling results in a fine grain and a more uniform coloration.

Image Source: Earth at Home Geologic map of Wisconsin showing maximum ages of mappable units. Image by Jonathan R. Hendricks for the Earth@Home project developed using QGIS and USGS data (public domain) from Fenneman and Johnson (1946) and Horton et al. (2017).

Why is it Red?

The red in Wisconsin red granite comes from the minerals in the rock. Minerals are the ingredients in granite soup that interact to create the distinct crystal and color structure of the rock. Granite is typically a combination of three main minerals: feldspar, quartz, and mica. For our red granite, the color comes from the alkali feldspar. This type of feldspar is high in potassium and is often present in granite with the red to pink hues we see in our Wisconsin red granite.

Don’t Take if for Granite…

Since 1971, Wisconsin red granite has been a state symbol, but its history and economic importance goes back much further. Red granite was long quarried in northern central Wisconsin and has been used to make anything from curbs to countertops. The red granite industry birthed several towns in the region whose economies were driven by quarries that dug into the bedrock of the communities. Red granite is cemented in our state’s communities. Th red granite we see in the hills of central northern Wisconsin was formed approximately 1.85 billion years ago by a chain of islands crashing into the Superior Upland. This makes the red granite it Wisconsin of the Proterozoic Eon–approximately 2.5 billion to 541 million years ago.

Granite is a critical resource to geologists in Wisconsin, particularly because of this timing. Some of the oldest rocks in our state are granite and due to the way they form–over a longer period of time, the rocks can tell geologists a lot about what the Earth was like during the time the granite was forming. The geologic record tells us that during this time, the plate tectonics of Earth were active with many of the land masses on Earth’s surface either crashing into each other (like our islands crashing into the Superior Upland) or rifting apart. 

From the countertops in your home to miles below the Earth’s surface, Wisconsin red granite tells a story billions of years long. Like so much of our geology, granite is a material resource and a historical resource, telling us about our home before we were even here.

For more on geology from a Wisconsin trained geologist, check out this podcast:

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News from Nature Net Members​​

For the first time, the Lussier Family Heritage Center will be offering a full summer of camps in 2024! The camps are geared towards ages 6 to 14 and will cover a wide range of topics. Follow along on their Instagram for weekly reveals of camp themes. Full summer camp details will be available in January.	Upham Woods is proud to partner with Access Ability Wisconsin (AAW) as part of their efforts to promote access through their programming. Upham Woods will hold accessible events at their site and host AAW’s all-terrain outdoor wheelchair (OWC). The OWC is available for reservation both on-site at Upham Woods as well as at off-site community events. Read more here!	The Aldo Leopold Nature Center is hosting its annual Holiday Market on December 3rd! Shop local and shop small this holiday season from vendors selling everything from locally grown foods to found-object art, from upcycled mittens to handcrafted jewelry. Learn more about the vendors and event details here.

More from Nature Net…

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Cozy up as a family this season with a good book. Inspire the young people in your life to find wonder even in the colder months with a book off our Winter Landscapes book list! Check out some of our other book lists to keep curious minds occupied through these chilly days.	Planning for field trips to Nature Net sites next semester? Check out our Nature Express Grant program to support your excursion. Grants can help cover bus costs, field trip fees, or nature-themed projects. More information available here!	Get ready for winter with events from our Nature Net members. Make winter bird feeders at Madison Children’s Museum or get a behind the scenes look at what goes into Olbrich’s Holiday Express Show. However you choose to celebrate, Nature Net has something for everyone!

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