A 12" slab of uncut peanut wood. Photo from geology.com
The bold patterns and high contrast of peanut wood is what first caught my eye, but I didn't really look into the origin of this beautiful material until recently - I just figured it was peanut wood that had been petrified. Nope! Of course, any type of petrified wood is always cool but there is so much more to peanut wood!
Peanut wood likely began as a conifer tree in Western Australia in the Cretaceous period, about 145-66 million years ago. It probably lived near a river, and when it died and fell the river carried it to a shallow salt water sea that covered much of the land at that time.
A pretty typical story so far, but once in the sea, our dead tree attracted the attention of some hungry marine clams. Their larvae sought out the wood and began to eat their way into it, leaving lots of meandering bore holes. You can probably tell where this is going...but there's a twist!!
After being munched on for a while, all the bore holes caused the tree to become water logged and sink to the bottom of the sea, which was covered by a very particular type of sediment made up of the microscopic skeletons of radiolarians.
Radiolarians are teeny tiny plankton with elaborate, silica based skeletons. When the plankton dies and the skeletons fall to the ocean floor they form layers of white sediment on the sea bed called radiolarian ooze. (Ooze!!) The ooze slowly filled up the bore holes and covered the wood, creating the perfect environment for fossilization.
Ten different species of Radiolarians from usgs.gov
Guess what radiolarians become when they turn to stone? Radiolarite! A stone made up of billions of little silica based critters' skeletons! And the material that makes up the "peanuts" in our peanut wood (which is only named that due to it's resemblance and has nothing to do with actual peanuts).
A nice specimen from outbackmining.com showing the bark and tree rings.
So after all these processes and lots of time, we end up with petrified wood full of trace fossils of the bore holes of ancient clams that have been filled in with the fossilized skeletons of countless plankton. Phew! Such an incredible story of Earth's past in one pretty little package!
I think I'll be working with this fossil a lot in the future, click here to see if I have anything currently available, or send me an email to request something made just for you!
P.s. The whole region of Australia where this shallow sea once covered the land eventually got uplifted to around sea level and it is now called the Windalia Radiolarite. It's also where Mookaite formed, but more on that in another post ;)