Oakland Geology

Oakland’s buildings embody history and geology in the different types of stone that compose their facades. So how about granite?

California began producing granite soon after statehood, in a stonecutting district near Sacramento where rail and barge transport was handy.

At the time Oakland’s third City Hall was being designed, around 1910, many large quarries in the Sierra were supplying the market, and the architects chose “Sierra White” stone from a quarry near Madera, probably the McGilvray Quarry. The same district still produces Sierra White granite for the great Coldspring empire.

This fine-grained granite is excellent for carving and for resisting the attacks of urban pollution. Its neutral color works well with the building’s superb ceramic tiles and marble. Many of San Francisco’s notable buildings (the St. Francis Hotel, Bank of California and Old Custom House among them) also use Sierra White.

Buildings of later vintage take advantage of stone from more distant sources. The Lake Merritt Tower building at 155 Grand Avenue, built in 1990, features a splendid granite with extremely coarse grains, not typical of California. The granite benches around the building use the same stone in a polished finish that displays it especially well.

The building itself employs the same granite with a flamed or thermal finish. It’s produced by running stone slabs through a set of gas-fired torches. The sudden thermal expansion shatters the minerals and, properly controlled, yields this rugged surface.

The Caltrans building next door, formally named the Nicholas C. Petris State Building and finished in 1992, is faced with a pink granite from Texas in both polished and sandblasted finishes. Here’s a closeup.

What are we looking at here? Time for the geology part. First of all, to stone dealers “granite” means only one thing — a coarse-grained rock (1) hard enough to take a good polish and (2) not marble, serpentine or quartzite — but that thing is a very broad one. Stonecutters came centuries before geologists, and what they say goes.

Geologists don’t call every granite building granite. “Black granite,” for instance, is gabbro. Scrupulous geologists would call all the stones in this post “granitoid,” meaning one of a broad set of coarse-grained rocks made of feldspar and quartz in various proportions. Real petrological granite has a narrower set of proportions. None of these stones has the 20 percent quartz that would qualify it as true granite. I know you’re disappointed. But the feldspar makes a great building stone.

In the picture above, quartz is the clear stuff that looks gray. Feldspar comes in two main types. The white grains are plagioclase feldspar, and the pink ones are alkali feldspar. (A pink color is unusual; it ranges from white to buff to red.) The black grains are typically hornblende, biotite (black mica) or both.

The gorgeous Texas Pink granite of the Lake Merritt Plaza complex, at 20th and Harrison streets, shows these minerals more vividly.

I do think this is Oakland’s most beautiful building stone. Texas Pink is a brand (not the kind you burn on steers), also from the Coldspring empire. It’s quarried from Granite Mountain, about an hour out of Austin and near the amazing dome of pink granite preserved in Enchanted Rock State Natural Area.

Texas Pink granite was also used, a bit more adventurously, in the AC Transit headquarters building at 1600 Franklin Street.

I don’t know in what year the building was constructed, but I have the impression that Oakland architects are finished with Texas Pink granite for the moment. Metal and glass is the default exterior of today’s large urban buildings. In their lavish lobbies and interiors, though, stone is still the right stuff.

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