mlkgeo Posted January 16, 2023 Share Posted January 16, 2023 Hi, I've had this "rock" for about 2 years and it has been on a shelf reminding that I must find out what type of rock is this? How does two seemingly different rocks get merged like that? Thanks for any help! Regards, Mike Link to comment Share on other sites More sharing options...
jasong Posted January 21, 2023 Share Posted January 21, 2023 If I had to guess I'd say that rock wasn't merged, but grew more like a concretion on whatever the flatter rock is. There is also the potential it's some result of differential weathering/erosion where the rounded part is softer and the flat part is something harder like chert, and it spent time in a water course where the water rounded the softer part and the harder part was not as affected. But it looks more like a concretion to me. 1 Link to comment Share on other sites More sharing options...
Geologyhound Posted January 31, 2023 Share Posted January 31, 2023 My first inclination is that the softer and lighter colored parent rock was fractured and the fracture was filled with the darker and harder material before this rock was separated from the original outcrop. This can happen with sedimentary and igneous rocks by different methods. As jasong mentioned, the rounding of the parent rock likely occurred by tumbling in a river or stream. I’ve also seen this kind of shape when an asphaltic layer with some included iron fragments picks up mud and rusts it all together into an iron concretion. But based on the picture, I think your rock is a weathered chunk of a filled fracture. Link to comment Share on other sites More sharing options...
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