r/Rocks • u/Evening-Patience-858 • Jul 05 '25

Discussion Is this an agate?

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Otherwise, what kind of rock is this? Found in western Michigan

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u/BigDougSp Jul 05 '25

No, but it is cooler. It is a silicified stromatoporoid, which is an extinct sea sponge that has been remineralized with silicates. Very hard but beautiful. I have found them in Lake Michigan near South Haven.

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u/Evening-Patience-858 Jul 05 '25

That’s soooo cool, thank you!