Agates in MN EarthCache
-
Difficulty:
-
-
Terrain:
-
Size: 
(other)
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
This EarthCache is wheelchair accessible and is accessible in all seasons. It is located inside the Visitor's Center.
Agates in MN
Agates have always been popular in Minnesota. We love to search for them and collect them. It is one thing that children and adults like to do together. How many people do you suppose have a lake cabin in Minnesota? Of those, how many have a jar of agates on a shelf in the cabin?
In 1969, the Lake Superior Agate, popularly known as a Laker, became the Minnesota State Gemstone. Lake Superior Agates may be the oldest type of agate known to us; geologists believe they were formed at least a billion years ago. Many collectors say that when you find and pick up a Lake Superior Agate, you are the first person in a billion years to touch it. This certainly adds to the mystique or romance of the beautiful agate.
Uniquely characteristic of Lake Superior Agates is their color. Their main colors are bands of red, orange, yellow, and/or rust. Another characteristic of the Lake Superior Agate is its wide distribution throughout Minnesota; actually, it can be found as far south as the state of Kansas. This wide distribution encourages us to look for them. While we frequently find them on lake beaches and along rivers and streams, we should not forget that we can also find them in gravel pits and in our yards and gardens.
In the distant past, tectonic forces opened a rift valley that ran north and south through Minnesota. The northeastern part of the rift valley is known as the Superior Trough and forms the bed of Lake Superior. It is here that Lake Superior Agates were formed in Minnesota. As the walls of the rift valley spread apart, lava oozed into the floor of the valley. Bubbles formed on the upper layer of the lava; as the lava cooled, the little bubbles filled with water vapor and carbon dioxide. Geologists call these pockets vesicles. Over time, groundwater carrying dissolved minerals and quartz filtered through the vesicles that the bubbles left. Gradually, the quartz and minerals crystallized into patterns inside the pockets, forming a fine-grained chalcedony with interesting patterns of bands. These nodules are a precious stone or gemstone that we call Lake Superior Agates.
Lake Superior Agates are classified by the pattern of banding in them. Some of the most popular ones are:
1. fortification agates, which have bands that form concentric patterns. They somewhat resemble the walls for a fortress.
2. eye agates, which are specialized fortification agates. Their bands are round and frequently have a white band that makes them look like eyeballs. They are not as common as other forms of agates.
3. water-level agates, which are another, specialized fortification agate. The bands are parallel and straight. The quartz and mineral rich water collected inside the pockets in little puddles that crystallized into layers. They form solid little levels that tell us about the position in which the agate formed.
4. moss agates, which are specialized water-level agates with inclusions of little bits of minerals. Frequently the inclusions look like little trees and other plants in the agate. Often a moss agate will look like a miniature landscape.
These are examples of agates from the collection of Harriet Noreen.
As soon as the agates formed in the old lava, erosion began to wear away some of the lava. The agates were much harder than the lava so they remained. Although some of the agates were freed from the lava matrix, many more remained trapped in the lava. As weather patterns changed and the temperatures became colder, snow did not melt during the summer. The snow accumulated throughout the year and slowly compacted into ice, forming the glaciers. Glaciers covered all of Minnesota except for a relatively small area in the southeastern corner of the state. The glaciers picked up the freed agates and moved them south out of the Superior Trough. In addition, the freezing and thawing action at the bottom the glaciers as well as the movement of the glaciers broke off chunks of rock with agates in them. As these chunks of rock churned inside the glacier, more agates were freed. The free agates inside the glacier were polished in the same way that they are polished inside an electric rock tumbler. They bumped against each other and other rocks as the glaciers moved; they were also churned inside the glacier with grit that was left from rocks that had broken apart.
As the temperatures began to warm, the glaciers retreated leaving enormous ice chunks as big as icebergs. These ice chunks contained soil, rocks, minerals, and agates. As some ice chunks melted, they formed lakes where we find agates that wash up onto the beaches. In other parts of Minnesota, the glaciers left soil deposits that covered the rock that was present with new soil containing agates.
Obviously since the agates formed inside bubble pockets in lava, most of them are small, pea-sized nodules. There are some that are large, weighing 20 pounds or more and there are some that weigh 2 or 3 pounds. There are still some medium to large agates waiting to be found.
Objectives of this EarthCache:
1. Basic knowledge of how agates were formed
2. Knowledge of where in Minnesota agates were formed
3. Understanding of why the agates came to be where we find them
4. Knowledge about how long ago agates were formed
You will be going to Moose Lake State Park. It is located east of I-35 at the Moose Lake exit #214. The park entrance is off County Road 137. Take the Moose Lake exit from I-35. Go east on County Road 137 until you see the park signs about 1/2 mile down the road.
At the posted co-ordinates, you will be in front of the door to the Moose Lake Agate and Geological Interpretative Center located inside Moose Lake State Park. In the interpretative center you will learn more about agates and Lake Superior Agates in particular. You will also learn about the geological history of Minnesota. To access the interpretative center, you will need either a daily park permit or an annual park permit. Daily park permits are available for $7.00. Annual permits are valid for a year from the date of purchase and cost $35.00. An annual Minnesota State Parks permit, giving you access to all of the state parks is one of the neatest things you can put on your windshield.
Park Hours, Memorial Day through Labor Day:
Sunday – Wednesday, 10:00 a.m. – 4:00 p.m.
Thursday, 10:00 a.m. – 4:00 p.m.
Friday & Saturday, 10:00 a.m. – 4:00 p.m.
After Labor Day until Memorial Day, the building is open on a more limited basis.
The center usually is open periodically from 10:00 a.m. – 4:00 p.m. M, T, Th, F and Sat. If you call ahead to the park [218-460-7001], you may make arrangements to be certain the building is open for your visit. It is still possible that the staff member may not be in the center when you arrive. There will be a sign posted on the door telling you when the staff member will return. Use the time to hike in the park; Moose Lake State Park is a gem. In the winter, bring your cross-country skis or snowshoes.
As usual, observe the park rules during your visit. Collecting within Minnesota State Parks is not permitted in accordance with state law. If you have questions, please ask the staff.
To claim this EarthCache, please send the answers to the following questions.
1. What causes the characteristic red, orange, yellow, and/or rust color in a Lake Superior Agate?
2. Why is the Lake Superior Agate a good choice for Minnesota State Gemstone? Please give three reasons.
3. On the east wall of the Agate and Geology Interpretative Center is a timeline. Where on this timeline, would you place the development of Lake Superior Agates? Please note the answer may not be what you might expect based upon a geology lesson. If you are not certain about the answer, please send a picture of the timeline.
4. Post a picture of yourself (face not required) or a personal item
Additional Hints
(No hints available.)