Oakland building stones: Larvikite

3 October 2016

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.

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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.

larvikite-closeup

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.

larvikite-grave

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.)

The balsawood boulders of the Kaiser Roof Garden

26 September 2016

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Ever since 1960 when the rooftop garden on the Kaiser Center’s garage, largest in the world at the time, was built, it’s been heralded by American landscaping pros, Kaiser Center employees and appreciative residents. After the garden’s recent rehabbing, now (specifically, any weekday) is a good time to visit.

Putting a garden on a roof, even one made of the best Kaiser reinforced concrete, takes careful design and execution. The heaviest plantings and features were situated directly over the strongest supporting columns.

Even so, the designers had to minimize the weight of everything. The soil, a blend of lava rock, expanded shale and peat moss, is practically potting mix. The concrete is a lightweight formula. And then there are these impressive boulders.

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Each one is a generously sized hunk of pumice, the nearest thing to balsa wood in the mineral kingdom. Well, diatomite is lighter, but so friable you can crumble it in your hands. Pumice, basically a foam of expanded lava, stands up to weather beautifully with its relatively inert glassy composition. And close up, it’s handsome.

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If you see this stuff in a landscaping-supply yard, kick it around or pick it up. It’s so light, you’ll feel like Superman — but pumice will cut your bare skin, so be careful.

Oakland building stones: Sandstone

19 September 2016

For many years, timber was the default material for Bay Area buildings. Only substantial institutions like governments, banks and a few wealthy churches were sheathed in masonry — solid stone — and time and again, earthquakes were their undoing. Sandstone was chosen for the walls of two major Oakland churches, First Baptist and First Unitarian.

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First Baptist, on Telegraph Avenue at 22nd Street, was one of Julia Morgan’s earliest commissions, although she didn’t have a say in its looks. The Romanesque Revival building, inspired by the Aachen Kaiserdom, was designed by another architect whose delays in getting it built led the congregation to fire him once the exterior walls were up, in 1904. The day the church was to vote on Morgan’s design for the interior was 18 April 1906, and early that morning the San Francisco earthquake badly damaged the exterior. She took on the job of rebuilding it, then finishing to her own specifications a magnificent sanctuary inside.

The stone, to all appearances, is from the Greystone Quarry south of San Jose. It’s the same golden sandstone of Eocene age (~35 million years) used for the core buildings of Stanford University and other landmark structures like the Carson City Mint in Nevada, Lick Observatory and the old San Jose Post Office, now part of the San Jose Art Museum. I wrote about this stone for KQED a few years back. The stone blocks have a rugged “quarry face” on the exterior but are nicely dressed on the sides. The flat sides qualify them as ashlars, as opposed to fieldstone like you’d use in free-standing stone walls.

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The building also suffered damage during the 1989 earthquake. In this view you can see the seismic bracing, covered in gray, on the north wall that was installed at the time.

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The First Unitarian Church, at 685 14th Street, was designed by Walter Mathews in the elegant Richardsonian Romanesque style. Construction began in 1890.

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Stone was an important design choice, inspired by “a spirit of civic pride.” All of the building’s materials were sourced in California. The sandstone is a thick veneer, in quarry-faced ashlars like first Baptist. However, the stone is a cool gray, very fine grained, and is apparently not from Greystone Quarry. Parts of the building are faced in neat rows (courses) and arches.

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This stairwell bay is pleasingly laid in random-coursed ashlars, a system that avoids a regimented look and is probably stronger too.

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At its opening on 6 September 1891, a hymn written for the occasion began with the verse,

“The forests gave their oak and pine,
The hills their stone and clay,
And fashioned by the builder’s art
Our temple stands today.”

The building suffered light damage in 1906 and 1989, but repairs in both cases took several years.

The church’s Historic American Buildings Survey (HABS) report is full of deep technical and historical detail.

In both buildings, the sandstone shows signs of deterioration after more than a century of exposure.