Archive for the ‘Cemetery knockers’ Category

A real old-timer

15 April 2012

Mountain View Cemetery is a fun place for geology. Not only are there the untouched hillsides and the knockers of local bedrock, but the monuments themselves are displays of fine stone from around the world. On my last visit, though, this one caught my eye.

morton gneiss

It’s an example of the oldest stone in the United States, the Morton Gneiss from southwestern Minnesota. I mentioned it a few weeks ago in a KQED Quest Science Blogs post before finding this specimen. Touching it will put you in contact with something 3,524 million years old, more than three-fourths of the planet’s age.

Let me take this opportunity to plug Michael Colbruno’s blog about the people in the cemetery. He calls it “Lives of the Dead: Mountain View Cemetery in Oakland,” but I still think of it by its original (non-SEO-friendly) name “Mountain View People.”

Knocker 1 revisited

10 April 2012

In my latest serious walk through Mountain View Cemetery, I passed the first bedrock knocker I documented here as “my secret chert.” It’s no longer secret.

knocker one

Click the photo for the big version. The cemetery managers have been removing eucalyptus for some time, which I thoroughly approve. Eucalyptus isn’t a good cemetery tree: it’s messy, lanky, disruptive and incompatible with turf. But Franciscan chert is a good cemetery rock: it’s strong, silent, dignified and unfazed by anything. Anyway, now knocker 1 gets to bask in the sun again, and maybe its new visibility will gain it new friends.

Mountain View Cemetery knocker, the big one

10 April 2011

Since I featured what I called the big set of knockers (or in geology-speak, large competent blocks in Franciscan melange matrix) at Mountain View Cemetery, almost 3 years ago, the operators of the cemetery have opened a new premium section just below and removed most of the trees, unveiling the best rock on the hill. I visited it this evening. It’s still not much to look at unless you’re looking for it.

knockers

It’s mostly pale-green ribbon chert with some red chert. You might say the green rock has undergone a sea change. I’m not one of the experts in the Franciscan, but red rocks, which owe their color to trivalent iron (Fe3+), commonly turn greenish as the iron is reduced to divalent Fe2+, so I take it that this chert has undergone some challenging conditions in the ancient subduction zone that created the mixed-up melange. I find it harmonious.

green chert

Here’s a closeup. Click it for an 800-pixel version.

closeup

Stone like this doesn’t support a lot of life, being low in nutrients, but lichens have a foothold on it, especially where moisture can gather. The eastern, uphill side is like that, and the total impression, stone and sky and place and time, is most pleasing.

view

Again, click the photo for a big version. And visit the “cemetery knockers” category for the whole set.


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