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The formation of Lake Superior agates is a long, complex, and interesting journey. Here, we will explore how Lake Superior agates formed and were distributed.
The formation of Lake Superior agates began 1.1 to 1.2 billion years ago, so you could say that Lake Superior agates are almost twice as old as the first animals with multiple cells.
First, forces that manipulated the tectonic plates of the earth’s crust caused it to rip apart, from what is now Lake Superior to central Kansas. This area spanned almost 600 miles in length. Then, lava spilled out onto the land from that rip in the ground, slowly cooling to eventually become hard basalt, which is dark gray rock that is very common in Minnesota, that contained bubbles, alternatively called “vesicles”. These “vesicles” formed when carbon dioxide and steam were trying to escape the lava, but got trapped in the cooling process. Meanwhile, the sheer weight of this lava flow made a trough in the crust of the earth. Millions of years later, a part of this trough filled with water to form Lake Superior.
When the lava finished cooling, cracks formed in the lava-turned-basalt, creating a passage from the vesicle to the open air (and water). This happened because of contraction, or substances becoming smaller as they cool.
Next, the formation of the agates in the vesicle. This is when the debate begins.
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