Friday, January 9, 2009

First rock of 2009-Serpentinite

South side of the Mint (Safeway parking lot)

In addition to wanting to learn more about trees this year, I also want to learn more about rocks. Luckily, I can use kind of a similar approach to both subjects. Neither trees nor rocks go anywhere very fast, so I can use our vast collection of field guides to look stuff up post-wandering, and if I can't figure out what something is, I can go back and take another look (and maybe bring a camera).

Alright. First rock of the year is serpentinite, a hulking mass of which holds up the mighty Mint at Market and Dolores. It's a metamorphic rock found on the sea floor at tectonic boundaries. Serpentinite often contains veins, some of which may be filled with a form of asbestos called chrysotile.

Pay attention to serpentinite – if you see fibrous veins, don’t touch the rock.

I didn't see any fibrous veins in this rock, but I also didn't get that close. Not surprisingly, they have a big old fence around the Mint. And very stern looking guys with guns. They may even have guard crows. I kid you not, as I was walking around the building trying to find a place to take a picture a crow flew over me and dropped a rock square on the top of my head.

Little bit of trivia? It's the California state rock.

More trivia? This hill used to be 90 feet high, but they shaved off the top 40 feet to build the Mint. Our very own mountaintop removal project.


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