Until a few days ago, I always thought this was an agate. I tend to attract obsidian and have a lot of it. But this is the only piece I have seen that has both the reddish brown of mahogany and the white on black of snowflake obsidian in the same specimen. I only noticed because it is one of my windowsill gemstones which I trimmed down on after a recent house move. I never felt any deep connection to this stone. So it is time for it to find a new home.
The mix is quite uncommon. It's an interesting piece. I don't remember where it came from. I have been collecting crystals and volcanic glass my whole life.