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Minnesota’s Morton gneiss is one nice-looking stone

Quarried in Renville County, Morton gneiss is one of the oldest stones on the planet: about 3.5 billion years old.

Morton gneiss (pronounced “nice”), named for the town in Renville County where it has been quarried, is one of the oldest stones on the planet: about 3.5 billion years old. It is known for its beauty as an ornamental stone in buildings and monuments.

The rock known as Morton gneiss started out as a gray granite, formed about 3.5 billion years ago deep beneath the surface of the Earth. Molten rock cooled slowly, forming grains (granite comes from granum, the Latin word for grain) of crystallized minerals.

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About a billion years later, two fragments of the Earth’s crust collided at the future location of southwestern Minnesota, subjecting the granite to heat and pressure. These forces melted it once again and allowed intrusions of molten pink granite. The two granites folded and twisted; when they hardened (very slowly), the twists and folds remained. Eight hundred million years later, another geologic heating event added additional color and texture.

When cut and polished, Morton gneiss shows bands and swirls of black, pink, and gray, with white flecks, that sometimes look like galaxies and nebulae floating in the cosmos. The rock’s colors come from quartz (white), pink feldspar (pink), gray feldspar (gray), and biotite and amphibole (black.)

About one hundred million years ago, geologic forces slowly pushed Morton gneiss to the Earth’s surface. The glaciers that advanced and retreated across southwestern Minnesota between two million and 12,000 years ago covered the rock with hundreds of feet of soil and rock. The last glaciers began receding about 12,000 years ago.

A vast body of water known as Lake Agassiz formed in southern Canada, Minnesota, and North Dakota. When that water drained to the south, forming the River Warren, it carved out the Minnesota River valley. This powerful flow washed away hundreds of feet of glacial deposits and exposed some of the Morton gneiss.

Workers began quarrying this gneiss at Morton, Minnesota, around 1884. In these early years, railroads used it for ballast beneath railroad tracks. In 1886, the Swedish immigrant John Anderson arrived in Morton and took a job as a foreman in the quarry. It was located in the village of Morton, between the railroad tracks and the Minnesota River. By 1900, Anderson owned the quarry. He sold it to Cold Spring Granite Company in 1930.

Though Morton gneiss is as tough and durable as granite, it has rarely been used as a building stone. Architects have used it mainly in the lower floors of large buildings for its visual appeal. It enjoyed its greatest popularity during the Art Deco era of the 1920s and 1930s. Perhaps the most spectacular use of the stone can be found at the Adler Planetarium in Chicago, completed in 1930. Around the country it was used prominently in New York, Detroit, Des Moines, Birmingham, Tulsa, Milwaukee, Hartford, Brooklyn, and Cincinnati. It figures in two buildings at Washington State University in Pullman: Holland Library (1950) and its addition, Terrell Library (1994.)

In the Twin Cities, the stone was used by Northwestern Bell Telephone Company in its downtown Minneapolis and St. Paul headquarters. In downtown St. Paul, it was used at the street level of the West Publishing Company building on Kellogg Boulevard and in the original Ecolab Building at Fifth and Wabasha Streets.

Since the mid-twentieth century, Morton gneiss has been used more for grave markers and mausoleums than for buildings. At the Bird Island Cemetery, in Goodhue County, a free-standing arch of Morton gneiss greets visitors. The Wellstone family marker at Lakewood Cemetery in Minneapolis uses a large, uncut stone.

In Morton, the town’s welcome signs are made of gneiss, as are the front of the town liquor store and panels on the old high school. The stone is so plentiful there that it is used as riprap (erosion-reducing rubble) along ditches and streams.

Zion Lutheran Church may be the only building made entirely of Morton gneiss. The State of Minnesota designated a huge outcrop of the stone, in Morton, the Morton Outcrops Scientific and Natural Area. Visitors there can see Minnesota’s oldest rocks, eroded but unquarried.

Along with Kasota stone, St. Cloud granite, and Platteville limestone, Morton gneiss makes a distinctively Minnesotan contribution to the built environment.

For more information on this topic, check out the original entry on MNopedia.