Middlebury quarry demonstrates Omya’s range
Toolbox
By ELLE NOORDZY - Published: May 10, 2009
Take a tour through Omya’s Middlebury marble quarry, and you are stepping millions of years into the past, to a place where intense pressure and heat created a thick layer of metamorphosed calcium carbonate, now beautifully exposed on a 200-foot deep face. You may be very familiar with this rock, commonly known as marble. However, when crushed, this rock can serve some unfamiliar purposes.
Marble quarrying has a long and rich history, both on a global and local scale. Historically marble has been used for construction and sculpting, as it still is today. The famous Taj Mahal in India and the Venus de Milo sculpture are both famous examples. To a Vermonter, marble is fit for kings as much as it is for our nation’s capital, where it was used in the construction of the Thomas Jefferson Memorial, U.S. Supreme Court, and U.S. Senate office buildings.
Vermont marble put the industry on the map in the United States. The White Pigment Company joined the ranks in the mid-1800s, quarrying the marble for dimension stone. The quarry closed for a while, and then reopened in the mid-1970s under Omya.
At the site of the Middlebury quarry, a small-dimension stone quarry was opened in the mid-1800s. But because of commonly occurring fractures in the marble at this location, the quarry was closed after just a few years. The White Pigment Company reopened the quarry in the mid-1960s to quarry, crush, and grind the marble to a powder to produce calcium carbonate as an industrial mineral. In the mid-1970s, Omya opened a second quarry right next to White Pigment’s quarry for the same purpose, and ultimately purchased the White Pigment Company and developed the two quarries into one larger operation.
Unlike White Pigment Company, which selected only the whitest material, Omya wants to maximize the quarry’s yield to minimize waste. The quarry has different layered colors of pale pinks, salmon, and grey-blue because of different mineral impurities. On your tour of the marble quarry, you will notice bright white layers to the west, and gray layers to the east. Omya geologists have figured out how to blend the differently colored layers to make a powder of acceptable brightness and color. With this increase in efficient use of their resource, the quarry has 50 to 100 years of productive mining left.
Before the subtly colored stone can be crushed into a useful powder, it must be blasted from the marble faces of the quarry pit. Occasionally, the blasts can be heard or felt by nearby homeowners, but the blasts are regulated to be well below damage-causing levels. Huge dump trucks then cart tons of broken rock up from the working zone of the quarry and dump it to be separated and crushed into gravel-sized pieces. From there, it is mixed according to the geologist’s “color recipe” and then trucked to Florence to be crushed into white calcium carbonate powder.
What are the environmental effects of marble quarrying, and how does Omya mitigate potential problems? Beyond the rock itself, the two most valuable resources at the quarry site are water and soil. Excess water must be pumped out, or the quarry would fill with water and soon resemble the old West Rutland quarries. The water from the Middlebury quarry is pumped out, and a neighboring farmer often uses some of it for irrigation. Dissolved calcium in water has an added benefit to plants. The water is used to wash trucks before they exit the quarry and also to keep the dust down in the quarry on dry days. Air quality regulations require that the dust be regulated as a silicate rock, even though the calcium carbonate contains only a trace of silica. The topsoil that is removed from above the western working part of the quarry is being used to create new farmland to the east of the quarry. Any remaining topsoil that gets removed is stockpiled for future reuse.
After your trip to the quarry, you may return to town and run a few errands. You might be surprised to find that you are still looking at calcium carbonate, as it is used in many everyday products. Some foods and medicines contain calcium carbonate, such as cereals, toothpaste and antacids. Osteoporosis medications use calcium carbonate because of the bone-benefiting calcium. The fine powder is also used in paint, as it makes the paint more opaque so that it covers surfaces better. It is also added to plastics as a filler and strengthener to reduce the amount of petroleum required. Calcium carbonate in paper reduces the amount of trees needed, and it can also be used to make biodegradable Styrofoam-like plates that do not use any petroleum at all. So the next time you reach for your toothpaste, note that the tiles or countertop are not the only places where you may find marble in your house!
To get your own tour of the Middlebury quarry, Omya is planning its next quarry “open house” for Saturday, Oct. 17, 2009, as part of the annual Earth Science Week celebration.
Elle Noordzy is a third-year student at Castleton State College, where she is majoring in environmental science.
ON THE NET
Vermont Geological Society
uvm.org/vtgeologicalsociety/
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