strange rock egg shape clear pattern ?

Asked September 4, 2019, 9:15 PM EDT

i have found what i believe is a rock in the shape of a perfect egg but a raised octagon pattern shape all the way around it. wanted to know if theres a way to identify it.

Oregon geology

3 Responses

Hello! An image would help with the identification. It's difficult to say what mineral created the octagon pattern on your round rock. Minerals display in a wide variety of crystal habits. I suggest taking it to a local geologist for identification. Most U.S. Forest Service offices have geologists, as do the Bureau of Land Management offices and Natural Resource Conservation Service, if you don't have a local community or state college/university near by. The Oregon Department of Geology and Minerals Industry has a Contact Us and are very adept at answering questions. Have fun with your mystery rock!

thank you so much for the response! here are a few photos , it may have been easier with them posted in the first place lol. but i will definitely check out those places and suggestions for sure! thanks again.

Hi - This is most likely a geode. Another name is thunderegg. Geodes are generally gas pockets (vesicles) in volcanic rocks like basalt and rhyolitic tuff that have been filled with secondary minerals. The geodes can also form in sedimentary rocks. The secondary minerals are precipitated out of silica rich hydrothermal waters seeping through the cracks in the rock.
A local rock shop may be able to slice it open for you, if you want to see what's inside. Or you can imagine the hidden crystals and keep it whole. It's a nice specimen. Did you know that Oregon's State Rock is the thunderegg? Good question!