Agates, Jaspers, Chalcedony, Chert, and Opal have many similar characteristics and similar chemical structure. Even seasoned rock identifiers struggle at times with how to label and differentiate between these rocks. And sometimes a single rock may have agate banding, jasper outer layer, and a clear quart center; making it all three! And then there is that allusive Opal. Sharing the same silica based chemical structure, but with an added water molecule or two or three, it is softer and less lustrous. But it is closely related to the others and can look a lot like jasper or chert.
In this video, Shadow and I gather some rocks near a campground near Jacob's Lake, Arizona. We were on our way to Phoenix to visit family. We also took note of the surrounding geology which included a lot of calcite, limestone, malachite, and similar rocks to the rocks we gathered. Initially, I thought we found Opal. We took them home to test them.
Testing the rocks with hydrochloric acid ruled out that they were calcite based. Testing for hardness which placed them at a 7.5 on the Mohs scale ruled out that they were opal. Taking into consideration the calcite rich geology around the area, and the overall appearance of the rocks, I concluded that they are mostly chert with some Jasper. Maybe all chert.
Shadow and I welcome your comments to help us identify these rocks. Are they chert? Jasper? Something else?
We hope our adventure and testing these rocks might help others in learning to identify rocks. And, as always, we had fun! We hope you enjoy this video and subscribe and join us on future Adventures of Shadow.