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Sandstone, dolomite among construction materials in Butte
Photo courtesy of Dick Gibson. The sandstone in the gray entry arches at the Carpenters' Union Hall, 156 W. Granite St. — across from the Butte-Silver Bow County courthouse — was laid down in rivers near Columbus during Cretaceous time, about 70 to 80 million years ago.

Editor's note: The following is one of a series of columns from the Butte Citizens for Preservation and Revitalization.

While molten rock was solidifying to become the Butte granite 78 million years ago, sandy rivers flowing near what is now Columbus watered dinosaurs and primitive mammals.

And some of those river sands found their way to Butte — with a little help from an Italian-born quarryman.

Brick and granite dominate Butte's construction materials, but a few other natural stones are present as well. The entry arches and window sill courses at the 1906 Carpenters' Union Hall, 156 W. Granite St., are made of gray Montana sandstone, quarried near Columbus between 1890 and 1910.

Carved decorative vertical lines dominate the facade, but they do not conceal the original cross- bedding — angular trends in the fine-grained sandstone layers that reflect the currents in those 78 million-year-old rivers.

The quarry just north of Columbus also provided the stone for much of the Montana State Capitol in Helena. Michael Jacobs (born Jacobucci) came to Montana from Italy as a stone carver and mason, and eventually became a manager at the quarry around 1901. Jacobs became rich on this popular sandstone, finishing his 3,500-square-foot mansion in Columbus about 1907 and serving as the town's mayor in 1913-14.

A second unusual natural stone found on Butte buildings is dolomite, a rock like limestone but containing magnesium. The added magnesium makes it a bit harder and less susceptible to dissolution by the natural acids found in rainwater.

In Butte, the most significant architectural use of dolomite is in the cornices, lintels, sills and nameplate of the 1908 O'Rourke Building, 103 W. Quartz St., due east of the jail.

The creamy pink stone on the O'Rourke may be Tyndall Stone, a dolomite quarried near Winnipeg, Manitoba. But the O'Rourke is a bit early for Tyndall Stone, and the rock here does not display the fossils for which the Canadian material is famous. Wherever it is from, this dolomite adds a unique style to what was once a high-class apartment building.

Dick Gibson is secretary and webmaster for Butte Citizens for Preservation and Revitalization. For information about CPR, visit www.buttecpr.org. Office hours are Thursdays from 10 a.m. to 2 p.m., 405 W. Park St., Suite 200.

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