Green Rock
Let’s call it the mystery of the green rocks. We spotted them all over Big Bend last week as we drove in and out of the park and walked it’s hills. My friends asked about them because they know I like rocks. I took pictures when I could and tried to figure it out, but all I could do was guess. As a geologist, I’m an amateur, but I’m dedicated, and I happen to know several geologists and one of them works right down the road at the Blanco Pedernales Groundwater Conservation District. So, I walked down there yesterday.
Here's what I discovered. I need a loupe to get a close up look at the rock. I need specific information as to the location of the green rock. That places it in time and space. But given all that here’s what I discovered. There’s a lot of Tuff in Big Bend (picture above) because it’s an igneous rock formed as a result of ash flows from volcanoes. Sometimes it has a gray green cast. There were lots of volcanoes in Big Bend. Then there’s glauconite, and I love this. It gets its green color because it started out life as fecal material from marine organisms. Trilobite poop. There’s lots of sedimentary rock in Big Bend because once upon a time it was under water with trilobite’s pooping everywhere.
Now this won’t precisely answer anyone’s question about a green rock they saw, but it opens up a world of possibilities and that’s all I really need to get my mental juices flowing. I guess you can call this the curse of the curious. I love history and geology is the history of the world. And I like stories, and as stories go how our physical world came into being is a good one. So, now I’m going to see if I can understand the story, one rock, hill, mountain, and stream at a time. Seems a fun way to occupy my final years on this good, green earth.
John W. Wilson is the author of The Long Goodbye: A Caregiver's Tale