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2015741

Yule Marble

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2015741

Yule Marble

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Yule Marble

39°2.16′N 107°10.10′W / 39.03600°N 107.16833°W / 39.03600; -107.16833 (Quarry site)

Yule Marble is a marble of metamorphosed Leadville Limestone found only in the Yule Creek Valley, in the West Elk Mountains of Colorado, 2.8 miles (4.5 km) southeast of the town of Marble, Colorado. First discovered in 1873, it is quarried underground at an elevation of 9,300 feet (2,800 m) above sea level—in contrast to most marble, which is quarried from an open pit and at much lower elevations.

The localized geology created a marble that is 99.5% pure calcite, with a grain structure that gives a smooth texture, a homogeneous look, and a luminous surface. It is these qualities for which it was selected to clad the exterior of the Lincoln Memorial and a variety of other buildings throughout the United States, in spite of being more expensive than other marbles. The size of the deposits enables large blocks to be quarried, which is why the marble for the Tomb of the Unknown Soldier at Arlington National Cemetery, with its 56-long-ton (57 t) die block, was quarried from Yule Marble.

Yule's quality comes at a high price due to the cost of quarrying in a high-altitude mountain environment. This challenge has caused the industry and the town of Marble to undergo many boom-and-bust periods since quarrying started in the mid-1880s, making the town emblematic of the economic fluctuations that beset a single-industry economy. Technology advancements in quarrying machinery and transportation have reduced, but not solved, the cost problem that afflicts the operation through the present.

The forces that created Yule Marble make it distinct from all other American marbles. It was formed by contact metamorphism, unlike Vermont marble and Georgia marble, which are the result of regional metamorphism, a process more associated with the orogeny and erosion of mountain ranges on a regional scale. Geologists still debate over Tennessee marble which did not undergo the same type of metamorphism, leaving it in a very unique property somewhere between metamorphic marble and sedimentary limestone.

In evaluating the marble cross-section, the United States Geological Survey found the marble is bounded above and below by unconformities. This lack of conformable contact resulted in the early dating of the limestone as Silurian rather than the currently accepted Mississippian. The lack of conformable boundaries in exposures along the Treasure Mountain dome explains the variation in reported thicknesses in the quarry area west of Yule Creek of 166–239 feet (51–73 m) about 2,000 feet (610 m) southeast of the quarry. The overlying Pennsylvanian Molas Formation was an argillite unit which was converted to hornfels and quartzite. Stratigraphically below the Leadville, the chert bearing Devonian Dyer Dolomite Member of the Chaffee Formation was altered by the metamorphism to impure silica-rich marble and occasional serpentine-bearing marble.

The Yule Marble is a metamorphic facies of the regionally distributed Leadville Limestone of Mississippian age deposited 350 million to 324 million years ago. The Leadville within the Yule area was transformed by contact metamorphism that occurred during the latest Eocene and Oligocene epochs (34 to 28 million years ago) associated with the intrusion and uplift of the nearby granitic Treasure Mountain Dome. The uplift of the Treasure Mountain Dome tilted the limestone away from the intrusion resulting in the marble bed dipping at an angle into the mountain. The marble unit along with older and younger adjacent units in the Yule Valley have a north-northwest strike paralleling the valley and variable dips of 35 to 50 degrees to the west-southwest. This local contact with the heat and pressure from the intrusion of hot granitic magma recrystallized the Leadville Limestone into a distinctive white marble. Although the Leadville Limestone covered hundreds of square miles and was the ore host at the Leadville mining district, the Yule Creek Valley is the only known location of marble in the region. When the magma cooled, it crystallized into granite.

This local geological activity resulted in a type of marble that is 99.5% pure calcite, with trace amounts of non-calcite inclusions (mainly quartz), and has a density of 170 pounds per cubic foot (2,700 kg/m3). The non-calcite inclusions were caused through penetrations along the seams created by the dome uplift rather than through metamorphic contact with the uplifted dome. Though marble is on both sides of the creek, the only visible marble is the 1-mile-long (1.6 km) seam of the present-day quarry on the west side of Yule Creek.

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