When a person thinks of agates Lake Superior agates probably come to mind or perhaps Montana agates. Not many among us would think of North Dakota. So one has to wonder how the North Dakota town of Agate got its name. Agate is just off highway 66 in Rolette County between Mylo and Bisbee. According to North Dakota Place Names by Douglas Wick, Soo Line Railroad workers named the town after moss agates that could be found in the area.
Agates are semi-precious stones that are used in making jewelry such as necklaces, pins, and rings. They are a brightly colored and fine grained form of chalcedony, a type of quartz, formed in cavities in volcanic rocks. As the cavity fills in with various layers of siliceous materials and minerals a layered appearance is often produced.
Moss agates are generally transparent to milky colored with inclusions of green colored material. Although the green inclusions may resemble mosses, these agates are not fossils. No moss material is in the rock, in fact, there is no type of organic material in the agate. The mossy looking material is the result of various mineral inclusions.
Moss agates may be found in the sand and gravel deposits along the Yellowstone and Missouri Rivers, especially near the confluence. Those from the Yellowstone River were likely formed in what is now Yellowstone National Park and washed downstream. The area around Cartwright, North Dakota is known for agates, and the area around Sentinel Butte is also known for having moss agates. A few Superior agates have even been found along the Red River and the beaches of glacial Lake Agassiz.
Rolette County is a young, glacial landscape. The moss agates found near Agate must have been transported to the area by the glaciers. It is interesting to note that Souris, Manitoba is well known for an agate pit near the town. That location is in on a glacial landscape as well. Perhaps it was the same glacial movement that dropped agates in both the Souris and Agate area. After all, these towns are around 60-70 miles apart. It might surprise you, but geologists use the type of rocks in a glacial area to help determine the direction of glacial movement.
As you travel the state, particularly in the Missouri and Yellowstone River confluence area or perhaps Agate, keep your eyes open for these interesting stones.
Natural North Dakota is supported by NDSU Central Grasslands Research Extension Center and Minot State University-Bottineau, and by the members of Prairie Public. Thanks to Sunny 101.9 in Bottineau for their recording services.
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