Can you help me identify this rock?

[cyndihaltom02]

It was suggested that I submit the following pictures to you to see if you might be able to help me identity this rock. I found it in Arizona about 15 years ago. It is a very large and heavy rock.

 

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[JiimmyTwoTimes]

I would say quartz. Not 100 percent.

 

[austin]

Yep, I agree with Jimmy. Partly quartz, maybe chalcedony too. Lots of it out west...

 

[Eu_citzen]

Looks like a mix of chalcedony and/or opal. A hardness test with a quartz should settle that. Get a scratch?
Yes. Opal
No. Chalcedony

 

[DDancer]

Layering suggests its more chalcedony than opal to me. Has some nice translucence.

 

[cyndihaltom02]

I looked at opal and was of the same opinion but I will look further, thanks for the feedback.

 

[unclemac]

flint nodule?