Last Friday at the Oakland Museum of California, I had the pleasure of giving a pop-up talk billed as “Artful Rocks and Rocky Art” that riffed off of my backstage experience with the UNEARTHED: Found + Made exhibit (going on til April 24). This was the only chance I’ll ever have to show my rock collection in a museum, and I’m very grateful to the museum staff for helping it happen.
I laid my four chosen specimens on a table and did an alas-poor-Yorick thing with each one. The point was to say something about what a geologist might see upon contemplating these stones, as a counterpoint to what a suiseki practitioner might see in a suiseki stone.
I went from stage right to stage left, starting with this piece of Orinda Formation conglomerate.
It exemplifies a lesson from Earth Science 101 that’s still the most profound thing geologists teach the rest of us. Conglomerate is a rock made of preexisting rocks — pebbles — and sand. The pebbles signal that a long-vanished mountain range once stood nearby, an upland which crumbled slowly into gravel that washed down riverbeds to rest in the sea. They were buried by more and more sediment deep in a seafloor basin, where the gravelbeds turned into new rock. And somehow, that rock was raised again above the water and became part of a new mountain, the Oakland Hills near Claremont Boulevard.
I summarized that with the singer Donovan’s rendering of an old Zen saying: “First there is a mountain, then there is no mountain, then there is.”
This sexy piece of serpentinite came second.
I explained how serpentinite arises when seawater invades the hot deep crust beneath the ocean floor, transforming its minerals from dark pyroxenes and olivine into the soft, scaly green translucent mineral serpentine, named for its resemblance to snakeskin. Later this material was vomited up in a seafloor mud volcano, then transported onto the land by plate tectonics where I found it by the road near Lake Berryessa.
Third was my pet cobble of laminated chert, mascot of my Facebook page. I found it long ago on a San Mateo County beach.
The multiple sets of layers in this silica-rich stone mark different events in its history. The earliest set is the fine laminations; perhaps they were annual layers left by a rich microscopic rain of dead diatom shells, or layers of them made by large storm events. The material, once buried, transmuted into chert under relatively mild conditions. Subsequently, and repeatedly, cracks formed across the laminations that filled with the same silica-rich material — earthquakes like today’s were the likeliest triggers. These veins are evidence of geologic conditions that extended across a whole region for a prolonged period in the deep past. Then the rock was uplifted. And then finally the pounding of cold surf sculpted the stone away until this smooth little nubbin was left. Nevertheless, it held enough evidence for me to visualize that whole lost land and history, as surely as the conglomerate told its tale of a mountain range.
Last was this unprepossessing bit of sandstone from Mountain View Cemetery.
It looks as ordinary as the sand in a riverbed, even under close inspection with a hand lens. But in the lab, the geologist can interrogate it with various microscopes and radiations that go far beyond the visible. People who have done that learned that this sandstone, the high-grade Franciscan graywacke found just up the hill, has its grains cemented together with prehnite. This is a mineral forms at great depth, and a testimony that rocks can be taken very far from their birthplaces and brought back to the light of day.
All four of these stones, then, tell stories that imply the action of slow, colossal forces that are constantly reshaping our planet’s surface. The real work of geologists is to understand those forces and work out their ramifications. The little stories lead to big stories that in turn shed light on the little stories. And that’s what these little geoseki mean for me.
My understanding of suiseki is as shallow as my understanding of rocks is deep. And suiseki practitioners don’t need any of my knowledge to pursue their ends. Our chosen beauties — their art and my science — are orthogonal to each other and that’s OK, because they still intersect. We are fellow appreciaters of rocks, and suiseki stones are as special as mine. Get yourself to the museum and take them in.
Oakland Geology 