The outer surfaces don't have the characteristic glassy conchoidial fractures. Your matrial seems to have a "powdery" look to it. The chips on the ground don't look right, either. It doesn't look like any of the Obsidian that I have ever seen.
Stunning depth of color, though.
Bob

This one is Pirhana Agate. It is about 3 1/2" wide.

This one is Biggs Jasper. It is 2 1/2" high.

This one is Morgan Hill Poppy Jasper. It is 3" wide.

This one is Montana Agate. It i 2 1/2" high.

this one is Brazilian Agate. It is 3 1/2" wide.

This one is Brazilian Agate. It is 5" wide.

Bob

Seth,
No, I don't use a light tent, just some photoflood lights. I tried a light tent and the reflection from the light was fuzzy and it implied that the polish on the stone was imcomplete.
Bob

I think the agate is from the Warm Springs Reservoir area in Oregon. I tried to maintain as much of the clear border around the white bands as I could. There were some black filled fractures on the bottom so I had to grind quite a bit into the "V" area to eliminate them. This cab is about 1 3/4" tall. I try to emphasize the patterns within the material when I design the shapes for the cabs.
I also do a lot of very large cabs (up to 7" across) primarily for my gem show display case.
Bob

How about a white banded agate.
Bob
 

My name is Bob Rush and I have been a lapidary fo 50 years so far. I was taught how to cut and polish cabochons by my uncle in Oregon when I was a junior in high school in 1958. I started into jewelrymaking about 35 years ago and I have taught jewelry making, lapidary and casting in the Bay Area for about 14 years. I retired last July and moved to the Gold Country in the lower Sierras. I'm currently building a large shop area so I will finally have a comfortable,dedicated place to do all of my lapidary and jewelry work. I recently got my website up and running. It is bobspremiumcabochons.com
I'm looking forward to learing a lot from all of the knowledgable and talented members of this forum.
Bob