Found this cool rock

[Kevinrose.1]

Found this rock in the river while camping. Was just wondering if anyone could help identify?

 

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[Kevinrose.1]

Sorry forgot to say where. Found in Ten Mile Creek at Moose Creek Campground. Near Helena Montana. Outside feels like sand. Cant really tell about inside. Looks different in all different lights.

 

[HuntinDog]

Dino Dung