Our local geology is fascinating. We live along a narrow belt of serpentine that crosses through the Chiba peninsula. Nobody has quite figured out how it got here.
On Sunday, Tod & I joined Oyama Senmaida’s geotour – it’s a long-running program coming back after a six year hiatus. Geologists Naoki Takahashi and Nobuko Ushimura guided us on a hike along outcroppings of serpentine on the Mineoka ridge and Yaoka shore.
Serpentine is a “rock with a thousand faces,” as it can appear greenish from its olivine component but the iron it contains oxidises, turning it orange. Some rocks are black or grey-green on the outside and orange inside; some the other way around. I had a lot of fun smashing rocks open with Ushimura-san’s rock hammer.
After the ridgeline, we enjoyed lunch and then walked down the mountain to the beach, where we observed and collected stone samples. There is a lot of serpentine here
From the cliff above the beach we observed Matsushima and the tiny islands in the cove which are all different types of stone: tuff, sandstone, shale, basalt, gabbro, and metamorphic rock. We also visited an outcropping of pillow lava and learned how it was formed.
I brought home stones, of course. Some serpentine samples as you would expect. And also a massive 5 kg gabbro which I carried it up and down the hills from the beach so that I could put it in the garden. I spotted a couple of heart shaped rocks, and one with a marking like an eye. Kawasaki-san gave me a pink zeolite that he found. And I found a fossil on the beach, which Takahashi-sensei identified as a sea lily.
It was six hours of absolute delight. It’s Tuesday and I am still feeling happy about joining the geotour. Looking forward to the next one!
