This is a gorgeous specimen of Tube Agate. Very different. While most tube/moss agates are full of mossy, tube inclusions, this one of mostly solid. The contrast of the solid dark color with the white lines and cloud-like shading, along with the golden-tan color tubes, makes this a very eye-catching cabochon. Because of the reflection off the high polish, it was very hard to get a good photo of the shading in the stone. So I have provided several views so hopefully you can see around the stone.
It looks almost black, but it's a deep, dark, brown. The dark color is translucent and you can hold it up and see a bit of light through it.
This is a very striking piece and would make a very interesting piece of jewelry.