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Help ID'ing rocks in Colorado~!


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We recently moved back to Colorado,.,..


Got us a tumbler and rock saw and toys... but need help identifying some rocks -


These rocks looked like Petrified wood at first, but then we noticed the top crust has weird swirls /designs.


Upon tumbling some, we noticed that the striations and swirls on the crust are almost opalescent looking, hard to tell.


Anyone have any idea what these could be??






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Hi there! Welcome from Centennial, CO!


Can you post some closer photos from various angles of some of these pieces?


Any information you can provide about location and age of the sediments would be helpful as well.


I am especially interested in that pitted looking one on the left hand side!

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  • 2 weeks later...

Just saw this post, sorry for the late reply.

All your specimens are fragments of large inoceramid clams, likely Sphenoceramus.  The fibrous calcite structure is characteristic.  The "pitted" one has small oysters (Pseudoperna congesta) attached as epibionts, also a common occurrence.  



  • I found this Informative 1
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either Inoceramids or calcite layers.  Pretty common in Cretaceous marine rocks, of which there are an abundance of on the western slope. 

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