Every rock tells a story

Have you ever picked up a really interesting rock and wondered what it was and how it was made? Well, I have, and still do. Each rock tells a story about its creation: when it was made, how it was made, where it was made, and how it got to its finding spot. As I learn more about rock creation, I become interested in all rocks, even the plain ones.

One rock that is definitely not plain is our state gemstone, the Lake Superior agate. While visiting my son and his family in Omaha last week, my granddaughter and I found a Lake Superior agate - she is only 18 months old but spotted this tiny little agate in the pea-sized rocks in a playground.

As you can see in my drawing, Omaha is at the extreme southwest part of the Lake Superior agate distribution area and Cloquet is at the other end. Let's make an agate and figure out how it got from northern Minnesota to Nebraska.

The recipe for a Lake Superior agate is a closely guarded secret, but I was able to find the recipe and will share it with you. The list of ingredients follows:

1) hot lava with air bubbles,

2) vesicular basalt,

3) water with dissolved iron and silicon dioxide,

4) lots of time.

Let's jump into our time machine and travel back one billion years ago and watch the beginning of agate formation. When what is now North America tried to split in half (see mid-continental rift in the drawing), dense lava flowed up and out of this rift. As it cooled, gasses were released and formed bubbles. This cooled lava is the rock called basalt; basalt with bubbles is called vesicular basalt.

Now we are on Step 3 of our recipe. Over millions of years, ground water rich in iron and silicon dioxide seeped into these bubbles through microfractures in the rock. The silicon dioxide then crystalized while in the bubbles - silicon dioxide crystals are clear or white colored, and silicon dioxide containing iron is reddish in color. The red and white bands that give the Lake Superior agate its character is actually a combination of quartz and a more opaque variety of quartz called chalcedony. Over time, these layers grow from the outside of the bubble towards the center to make an agate. If the growth stops before the bubble is filled, we call it a geode, or a hollow agate.

All we need now is something to release these agates from the basalt and carry them to Omaha: enter the glaciers that ground out the agates and carried them to faraway places.

Agate hunting is fun and we live in a great place for it.

The Moose Lake Agate and Geological Center in Moose Lake State Park is a fantastic place to learn about our geology and see some amazing agates and other rocks and crystals from our area. The Rock Place at the corner of Avenue C and Vine Street in West End Cloquet is a good place to see all kinds of rocks and agates, from near and far, and even purchase some.

Gravel pits, freshly plowed fields, gravel beaches and gravel roadsides are all great places to agate hunt. Free agate hunting permits are available online for three local gravel pits in the Moose Lake area. Make sure you bring a little kid with you: they have great eyes, are close to the ground, and make great agate pickers.

Remember, every rock tells a story.

The very curious 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. He's also a proud grandfather. His 18-month-old granddaughter, at right, has proven to be a good rock hunter.