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Rock in a rock
Rock in a rock  
I found a rock in a rock both look basalt i live in central Washington Basalt is the dominate rock up here.I was wondering how this happened.

Hi John,
It looks like a basalt pebble from an earlier eruption got covered in a subsequent eruption.

What usually happens is that a lava flow cools and erosion starts immediately.  That breaks up the rocks that the flow created and probably just left them in place.  Then another flow happened and covered the rubble.

Hope this helps.


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C. Robert Reszka, Jr.


I can answer any general geology question (rocks, minerals, stratigraphy, geomorphology etc.). My expertise is in the geology of the Michigan Basin, PreCambrian, Paleozoic and Recent. I can answer questions concerning mining and petroleum exploration and production and the laws concerning those activities. I can also answer questions concerning stratigraphy of the Michigan Basin. I will also answer questions about mineral and rock collecting in the Basin. I won`t be able to answer many specific questions on hydrology, geophysics or geochemistry. I may be able to answer very general questions in those venues.


I have been working for the State of Michigan for 36 years as a Geologist and a Resource Analyst. I have experience with Subsurface Geology and Petroleum Geology, mining in Michigan, and Sand Dune Mining and Protection issues.

Michigan Basin Geological Society

Decade of North American Geology.
Bedrock Geology of Michigan

BS Wayne State University

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