Oakland Geology

The building that houses Autotrends Body Shop, on Broadway’s Auto Row, is trimmed with larvikite, a remarkable decorative stone from the area of Larvik, Norway, in the southern part of the Oslo Graben.

It’s a steel-blue stone, just under 300 million years old, with flashing highlights from fingernail-sized crystals of feldspar. This closeup from the auto body shop shows the richly textured grains in detail. The many tiny dots are probably either dirt or paint spatter, so ignore them.

Other than the black grains, which are mostly titanium-rich magnetite and possibly augite, this rock is almost totally feldspar. The large feldspar grains are intimately intergrown crystals of orthoclase and alkali feldspar. These separated out (exsolved) from an initial material consisting of anorthoclase feldspar in microscopically thin layers (lamellae) as it very slowly cooled. Because the three feldspars occur together, this is called a ternary feldspar. (Feldspars are complicated minerals — there will not be a quiz.) The visible lines are tiny fractures inside the grains that are typical of feldspar.

The lamellae interfere with light in a way that absorbs red and yellow wavelengths. The remaining blue or green diffraction colors are what give the stone its gleam, a characteristic called schiller. The gemstone labradorite, another feldspar, also displays this kind of schiller.

Here’s a cleaner example from a gravestone I photographed at Evergreen Cemetery a few years ago.

This stone has been produced since the 1880s. Buildings all over Oslo, Sweden, feature green, blue and rare red larvikite. There is a large amount of quarry waste involved, which the locals use for everything from concrete aggregate to seawalls.

Larvikite is scarce in Oakland buildings, but you’ll see it as accent stones or in interiors. The bar at Club 21, for instance, is a gorgeous slab of it that glitters like a cosmos under the disco lighting. Think of happy dancing Swedes when you’re there for the monthly meetings of Nerd Nite East Bay. (I’ll be speaking there February 27.)

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