Montana Earth Science Picture of the Week

Grizzly Gulch Lime Kilns Provided Mortar for the Capitol

Photo by Keith Benson

Not that kind of lime. . .
When you hear the word "lime" you probably think of the green citrus fruit used to give 7-Up its distinct flavor. This photo, which was taken less than half a mile south of Helena, shows the ruins of kilns (ovens) that produced a totally different type of "lime". The type of lime produced here, calcium oxide (CaO), was used to make mortar that was needed to construct buildings of brick and stone in Helena during the late 1800s and early 1900s.

A little chemistry . . .
The kilns were built here because of the availability of the light-colored limestone, which can be seen on the slope behind the kilns. Limestone is a sedimentary rock primarily made up of calcite (calcium carbonate: CaCO3). Workers blasted or quarried the limestone and then hauled or rolled the rocks down the slope, dumping them into the tops of the kilns. Pine fires in the furnace beneath the kilns burned constantly changing the calcite into lime.

500 to 600 C
CaCO3 (s) -----> CaO (s) + CO2 (g)

After several days the powdered lime was shoveled into cooling sheds adjacent to the kilns. Once cooled, it was hauled to building sites around Helena, where it was mixed with sand and water to make mortar. Each kiln could produce about 20 tons of lime every eight hours.

A little history . . .
Irish-born James McKelvey leased and then owned the kilns, supplying the mortar used to build the State Capitol. Lack of railroad access eventually forced closure of the kilns around 1910. The blocks of sandstone used to make the Capitol came from a quarry near Columbus, Montana.

Mortar: a thick mud-like mixture of lime, sand, and water used to hold bricks or stones together as buildings are constructed

Cement: a powdery mixture that includes mostly lime, as well as other materials such as clay, gypsum, etc.

Concrete: mixture of cement, gravel (pebbles), water

Term: quarry


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By Rod Benson
Earth Science Teacher at Helena High School


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