After years of seeing the term “rotten granite” show up in bid ads, curiosity finally got the better of me and here we are, learning about rotten granite together.
Rotten granite is granite that has been so assiduously weathered that it crumbles to small-sized particles. If that doesn’t interest you, read no further and check out these recently declassified Area 51 documents and photographs.
Still with me? Good for you and your living brain. Now you’re going to have to give me the benefit of the doubt with some of this as I do not have the room (nor you the patience) to go into a deep plate tectonics/erosion and weathering discussion in regards to rotten granite. So trust me: Wisconsin used to be near the equator between 1,400 million and 500 million years ago. Look up the supercontinent Pangaea if you don’t believe science.
But before that, about 1.5 billion years ago, magma from volcanoes was intruding into many areas of what would become the Midwestern U.S. granite crystallized from this magma at very shallow depths and after the magma cooled, these granite strata were subject to extensive periods of weathering and erosion.
Back then, the area that would become Wisconsin was in a tropical environment that predated land-covered vegetation, causing more intense weatherization of exposed soils and rock formations. Feldspar took the hit more than other minerals due to this, and since feldspar is the “glue” that binds granitic rock together, this is where the rotten bit of our granite lesson starts.
Without the feldspar to hold it together, the granite started to crumble.
Spanning millions and millions of years, a plethora of this rotten granite eroded away due to the rivers, lakes, seas and multiple glaciations events that impacted the area which would become Wisconsin. Some areas escaped these intense erosion processes and some rotten granite was buried under sediment, where it can be mined for today’s needs.
Rib Mountain (one of the oldest geologic formations on Earth) is the foundation of a 1.5 billion year old mountain range that has eroded away to its base through wind and water erosion over thousands of millions of years and it helped shield some deposits of rotten granite from erosion processes.
The Wausau area of Wisconsin is famous for it’s rotten granite deposits. Rotten granite is extensively quarried at several locations in the Wausau area and is almost immediately ready to be spread on driveways, roads, and children’s playgrounds.
Exposed deposits of rotten granite can be found near the surface along a creek running through Irving Park in Chippewa Falls or just look for rotten granite beneath your feet the next time you are walking down a gravel road near Wausau.
Many municipalities are seeking bids on rotten granite right now. Just log-in to JobTrac and run a search for rotten granite.
Jeff Moore is a data reporter at The Daily Reporter. He has been collecting rotten granite for years and will someday redo his countertops with it.