Walk through the National Gallery of Art's new Sculpture Garden on the Mall and you'll probably notice the 17 artworks and the fountain, not the marble.

But the rare stone that was used to build the garden has its own story -- one that reaches back decades, involves unexpected technical challenges, and has helped to revive two long-dormant quarries hundreds of miles away.

"The position of all the stone experts was that this couldn't be done," said Jerry Hunsberger, senior project manager for Tompkins Builders. The District firm was general contractor for the project, which cost $13 million, not including the art.

The garden sits on six acres between Seventh and Ninth streets on Constitution Avenue NW, just to the west of the National Gallery's two existing buildings. The older of the two is the West Building, opened in 1941. Like many of Washington's other monumental structures, it was built using one of the grandest and most expensive of stones, marble -- in this case, Tennessee Pink marble, quarried on the outskirts of Knoxville.

When architect I.M. Pei designed the East Building, which opened in 1978, he specified marble from that same quarry as one way to visually tie his modernist masterpiece to John Russell Pope's neoclassical structure.

So when designers began work on the long-planned garden, it was natural to specify Tennessee Pink marble. "One of the interests the design team had was to make the Sculpture Garden part of what we call a campus extension," said Carl Campioli, the National Gallery's assistant senior architect.

But there was a problem with that: The garden would require more than 500 tons of marble and Tennessee Pink was difficult -- some thought impossible -- to get. From its heyday in the 1920s, the Tennessee marble industry began declining during the Depression and war years. The weakened industry was further battered by cheaper foreign imports in the 1970s; by the early 1990s, there were almost no active quarries.

In addition to economic concerns, marble is a finite resource -- once it's quarried, it's gone. "One of the concerns was the quality of stone -- the really choice stone had been picked over," Campioli said.

Still, the National Gallery specified Tennessee Pink marble for the garden when it solicited bids in 1997. Tompkins, which had also been the contractor for the East Building, bid even though company officials knew it might be difficult to get the stone, Hunsberger said.

But even before making the formal bid, Tompkins contacted the company that controlled the quarry that had produced the stone for the other two buildings, Tennessee Valley Marble Inc. of Friendsville, just outside Knoxville.

The company, which also quarried limestone in Alabama, was getting back into the marble business, and wanted to take on the job in part to prove that it could provide enough marble for big projects.

Dennis Marsh, operations manager for Tennessee Valley Marble, explained that the privately owned company was formed in 1994 to begin producing marble, mostly for renovation jobs. At first, most of the stone came from unfinished, already quarried blocks available in the region, purchased from quarry owners.

Hunsberger and Campioli both made several visits to Tennessee Valley's Alabama plant in 1997 to determine whether the company and its stone met their standards, and in 1998 to oversee details. They examined samples of stone, both wet and dry, to see the full range of colors. (The stone is most colorful when it's wet.) Tennessee Pink's shades range from pale pink through tones of brown to a darkish color known as cedar.

As they looked at samples one day in 1998, Campioli said, "it became evident that we were really going to be tight on good clear pink stone."

The idea arose -- no one recalls exactly who came up with it first -- of using all cedar-colored marble on the garden's terrace walls. "It would free up a lot of the really clear stone" for some of the other structures that ring the garden, Campioli said.

"The really positive thing, when we left that day, was that we had fairly good assurance that there was enough to really do the job."

But there were other technical problems. Although Tennessee Valley already owned much of the state's marble, bought block by block, "for this project, they realized they would have to open another quarry or two. They invested a lot of money upfront before this job was ever bid," Hunsberger said.

Marsh won't talk about financial details, but his company reopened two old quarries, largely for this project. It hired about 25 people -- quarrymen and stoneworkers, many of whom still live in the Knoxville area. And it built a plant near the quarries for those artisans to do the detailed hand finishing that marble requires.

Just getting the stone out of the ground presented its own challenges. In the form that it was quarried, much of the marble did not meet the National Gallery's standards. Marsh said his firm had to quarry more than 50,000 cubic feet of stone to get the 6,000 cubic feet the garden required. The rest was waste, or material for jobs with different standards. Still, 6,000 cubic feet of marble translates to 510 tons of stone.

On a recent sunny day, Hunsberger walked around the garden, looking not at the statues, but at the stones. He splashed water from the fountain onto the different types of stones, demonstrating the striations of color and the shades in each type of marble. "See how pretty it is!" he exclaimed.

Down in Friendsville, Marsh said the project is more than art -- it's also proof Tennessee marble is again a viable construction material. His company's quarries are still running, both to increase inventory and to fill orders for projects. Those include not only repairs to historic buildings, such as the National Archives, but also some new construction -- office buildings in Knoxville, and a part of an office tower under construction at 2099 Pennsylvania Ave. NW.

The sculpture garden, Marsh said, "answers the question, is it available or not? That job made a statement that it is available and can be done in large quantities in very complex shapes."

CAPTION: "Puellae" (girls), one of the 17 artworks at the National Gallery of Art's new Sculpture Garden, stand in front a fountain made with Tennessee Pink marble, which is most colorful when wet.