Archive for the ‘oakland stone’ Category

Another appearance of the Morton Gneiss

25 May 2012

Not long after I documented the tombstone at Mountain View Cemetery made of the extremely old Morton Gneiss, I spotted the same stone—four polished disks of it—flanking the entryway of a house in the Grandview neighborhood.

morton gneiss

This stuff is certainly a gift to the world. And yet just today I bent down by someone’s fence to caress a boulder of our own red chert, equally striking in its own way.

Slate on the water

19 May 2012

Lately the city has been fixing up the walks along the waterfront, and they’re well worth a visit. This splendid boulder of slate isn’t on the newest part of the trail—it’s at the foot of Alice Street, just where the Jack London Waterfront leaves off and the Alice Street Mini-Park starts.

slate boulder

I don’t know where they get stones like this; they aren’t from Oakland or even from the Bay area. That’s OK.

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.”

Slate fountain

23 November 2011

Here’s a nice piece of stonework on upper Lakeshore Avenue.

slate fountain

It’s a pit lined with picturesque cobbles and rimmed with gray slate flagstones. A large slate boulder is mounted in the center, and a fountain trickles off a smaller slate stone over the boulder, cascading into the pit with a delightful sound. Thanks for the gift to passers-by.

Sidewalk weathering

18 October 2011

I look at sidewalks more closely than most people. It has little to do with geology, though—it’s just part of my hobby. But sidewalks do have geological lessons in them. Consider this sidewalk on the north side of upper Broadway near Lake Temescal.

sidewalk weathering

It has a series of light-colored wedges along the fence, on the uphill side. As you might guess, they reflect the pattern of the rainfall and its drainage. Fresh concrete is poured and then caressed with trowels as it begins to cure. This treatment pushes the larger particles of aggregate under the surface and creates a smooth finished surface composed of fine particles and cement. But the surface tends to weather off, partly because the surface is hard to keep moist for proper curing. The imperfectly cured material is prone to attack by rainwater, which is a mild acid. As rain and wind work into the surface, green things both microscopic and visible colonize the rough spots. These turn up the acid attack with exceptionally high CO2 levels similar to those in soils, along with humic acids produced by plant tissues. With time, the crisp white walkway turns rough, variegated—and beautiful, akin to natural stone.

sidewalk weathering


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