I wish I could recall for sure where I found this. Most of my collection is from tide pools and coves on the West coast of the US but it could possibly be from Zion National Park in Utah, Kern River in CA, or a number of other places but those listed are most likely.
It’s porous, lighter and slightly warmer than stone. The dark red areas are striated and softer than the rest. It does resemble some photos I’ve seen of agatized red horn coral, but I’m not sure. Any ideas or suggestions are welcome.