Weird rock from Malibu. Can you explain it?
So, when I was in Malibu, CA the other day, we took a quick sojourn to the beach where I picked up a few neat looking rocks off the shore. Three of them were fairly typical smooth, shiny or flat stones that you find at the beach. The fourth is unlike any rock I've ever seen. After doing a little googling, I'm still at a loss for how it was created and what it's really made of, so I thought I'd turn to the flist to see if anyone has suggestions. I'm unlocking this post in case any of you have any geologist friends you can link this to. I suspect it's some sort of sandstone, so I'm mostly interested in how the heck did it do that?
The dark banding wraps all the way around the light banding (or vice versa) like a snake
The two colors just spiral around each other.
Holding it, for scale.
It's a very cool rock. I'm sure it has to do with sedimentation, but I've never seen anything like it.
Different lighting.
On it's side. I'd guess the dark band was volcanic somehow, but it doesn't feel it.
In direct sunlight.
Thoughts? It feels like a typical sort of grainy sandstone and isn't especially heavier or lighter than anticipated. There are small chunks of quartz-like material throughout it, which you can see in some of the pictures. There doesn't feel to be an obvious divide between the two colors. If I hadn't picked it up on the beach myself, I'd honestly think it was somehow man made. I suppose it's always possible someone put it there, but it was a nearly empty beach in winter in a difficult-to-get-to area and just after sunset, so that seems pretty unlikely.
Anyway, got any thoughts on how that cool spiral motify formed?
The dark banding wraps all the way around the light banding (or vice versa) like a snake
The two colors just spiral around each other.
Holding it, for scale.
It's a very cool rock. I'm sure it has to do with sedimentation, but I've never seen anything like it.
Different lighting.
On it's side. I'd guess the dark band was volcanic somehow, but it doesn't feel it.
In direct sunlight.
Thoughts? It feels like a typical sort of grainy sandstone and isn't especially heavier or lighter than anticipated. There are small chunks of quartz-like material throughout it, which you can see in some of the pictures. There doesn't feel to be an obvious divide between the two colors. If I hadn't picked it up on the beach myself, I'd honestly think it was somehow man made. I suppose it's always possible someone put it there, but it was a nearly empty beach in winter in a difficult-to-get-to area and just after sunset, so that seems pretty unlikely.
Anyway, got any thoughts on how that cool spiral motify formed?