What is this rock???

by Rosie

I found this rock in the Thames and I really want to know what it is; no one at my university knew and they are curious now too!!! I would appreciate any help you can give.

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Nov 23, 2020
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by: Douglas

Rosie,

River rocks are a little harder to identify because their origin is unknown. Your specimen has 2 distinct parts: the white outside layer and the inner yellow-brown center. I will take a guess and say this may be a chert nodal covered by limestone.

Your mission should you choose to accept it is to test my theory.

The limestone can be verified by scraping off some into a small pile and add a few drops of vinegar. If it fizzes it is limestone.

Chert is very hard. It is a microcrystalline form of quarts. A scratch test will help to verify this. Learn about mineral testing here:

https://www.rocksandminerals4u.com/properties_of_minerals.html

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