Rock on! Discovery of white quartz a happy surprise

Last time we were together, we explored the formation of the unique bedrock of downtown Thomson. We traveled in the time machine of science and saw 2-billion-year-old mud compressed into shale, then cooked and deformed about 1 billion years ago, turning into slate. Now it is exposed in the St. Louis River in Jay Cooke Park and lines the community of Thomson.

After that journey through time, I hopped into my Dodge Dakota, left Thomson, and traveled less than a quarter of a mile before I got distracted again, this happens often to me.

As I was driving over the St. Louis River on Highway 210 I spotted a huge white rock at the base of the Thomson Bridge. "That is a huge vein of white quartz," I said to myself as I scrambled down the river bank to get a better look.

The best way to experience it is to stand on it and touch it. You can pull your car over on the Carlton side of the bridge and scamper down the upriver side. Another great way to see this formation is to park at the end of the parking lot for the UMD Outpost (White Water Paddling Center). From here you can look across the river and you will see a very large white area amidst the gray bedrock. It almost looks like someone spilled a few buckets of white paint. It isn't white paint, it is a huge vein of white quartz that probably even has a very small amount of gold mixed in.

How did it get there, how old is it, and is there any gold, were some of my questions as I stood on this large formation of beautiful white quartz. The exposed quartz formation is about 50 feet long and 10 feet wide. I don't know how deep it plunges into the crust and we don't know how high it went because a glacier ground it down to its current position.

We know from our visit to Thomson last time that the gray rock surrounding the quartz is indeed slate. It was mud, then shale about 2 billion years ago, then became slate when it was cooked and deformed when North America tried to split in half about 1 billion years ago.

The key event for the formation of that amazing chunk of quartz began after the slate layers were bent and deformed. During the deforming, large cracks would break within the slate. These cracks would later fill in with water: some of the water came from the surface in the form of runoff and some of the water actually came from deep magma cooling and releasing hot water from deep below.

Remember that I am in my time machine of science and I can see all of this happening. It's amazing. This water in the crack is not pure: it is very hard, full of minerals and some of it was very hot. As the water evaporated, it left behind deposits of minerals, like it does in my pipes at home. One of the minerals deposited when the water evaporated from our crack was silicon dioxide, also known as quartz. Now the fresh snow on the ground has covered our formation, but next spring or summer, check it out.

I am off again in my truck; if I am distracted I will let you know in a couple of weeks. Let me know if you find any cool places in the area.

FDLTCC science tutor Glen Sorenson was Minnesota Teacher of the Year before he retired from teaching science at Proctor High School after 30-plus years. He is an avid outdoorsman who most recently coached the Lumberjacks Nordic ski team. Contact him at [email protected] or leave a message for him at the Pine Knot News office at 122 Avenue C in Cloquet.