What is this one?

[crystalraye0379]

Found near the northeastern Colorado/Wyoming border.

 

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[Eu_citzen]

Looks like a silicate. Chalcedony? Common opal? Hard to tell. I suggest a hardness test with a known piece of quartz.
Opal is soft, easily scratched, chalcedony is not.

 

[DDancer]

Considering where you found it I'll side with chalcedony and what appears to be on the border of a jasper rind.... almost an agate. As EU points out opal is soft, test the clear areas with a bit of quartz~ chalcedony wont scratch easily but opal will. Let us know.