Volcanic rock?

[Daprezident661]

 

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[Indian Steve]

Not sure. Could be mahogany obsidian.

 

[DDancer]

Banded jasper. Not volcanic but a handsome piece. The detail is in the third picture.

 

[Tigger]

Not sure. Could be mahogany obsidian.

yep, looks like it to me.
If it's weathered, it doesn't have the sheen and sharp edges. Here is a cool reference that shows some colors obsidian comes in, not a complete list, but it talks about a great place to collect in Oregon that is just loaded with obsidian. We didn't find all the different colors, but were only there a day.
Obsidian

 

[stefen]

Isn't obsidian a volcanic by-product regardless whether its mahogany patterned or simply a single hue?

Wiki states that "Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock."

 

[Tigger]

Isn't obsidian a volcanic by-product regardless whether its mahogany patterned or simply a single hue?

Wiki states that "Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock."

Yes, obsidian comes in a variety of colors and can be solid colored or patterned. I didn't see that DDancer posted while I was typing, and usually I bow to his expertise, but this time it's easy to test. Pick your least favorite side, and chip a small piece off of it.

 

[Las Vegas Bob]

See if you can get a small piece to break off, if it is Obsidian it will break with a conchoidal fracture.

 

[bammer]

Possibly obsidian but lack of fractures give me doubt. The Jasper thought is probably correct being from CA. I may also suggest a BIF (Banded Iron Formation). Is it heavy and metallic looking in the dark areas? How about magnetic?

 

[Eu_citzen]

Rhyolite can also have flow-banding. Although most I've seen have been thinner.

 

[Daprezident661]

Yes, obsidian comes in a variety of colors and can be solid colored or patterned. I didn't see that DDancer posted while I was typing, and usually I bow to his expertise, but this time it's easy to test. Pick your least favorite side, and chip a small piece off of it.

But I like all sides ....

 

[stdenis_jd]

I'm no expert by any means, but I'm 99% sure this is a Jasper. My collection mainly consists of Jasper conglomerates aka drummond island puddingstones which are chock full of black, red, and pink Jaspers. This has the same structure as the larger pieces of Jasper I've found.

This is a terrific specimen IMO. If I found one of this quality in Michigan it would be a prize.

Not sure what hardness obsidian is, but I'd guess it is much lower than Jasper which is really just quartz with impurities (black and red usually indicates hematite and iron). If its Jasper it should be roughly 6-7 on the Mohs.

 

[stdenis_jd]

Just found this image of a "jaspilite" which looks a lot like what you have: