A court spokeswoman says architects figure a 12-inch-by-ten-inch section broke from the facade and shattered into about 40 pieces when it hit the steps below. Although it landed on the steps near visitors waiting to enter the building, no one was hurt.
The Architect of the Capitol's office is inspecting the damage and trying to figure out what happened. A spokeswoman says there was a routine inspection of the area about two years ago.
It's not clear if the accident has anything to do with the $122 million renovation under way at the 70-year-old Supreme Court building.
CBS News Radio correspondent Barry Bagnato reports that visitor were immediately shooed away from the site of the debris, which weighed an estimated 170 pounds.
The chunk of basketball-sized Vermont marble was part of the dentil molding that serves as a frame for nine sculptural figures completed in 1935. The piece that fell was over the figure of Authority, near the peak of the building's pediment, and to the right of the figure of Liberty, who has the scales of justice on her lap.
A group of visitors had just entered the building and had passed under the pediment when the stone fell at 9:30 a.m.
Jonathan Fink, a government attorney waiting in line to attend arguments, said, "All of a sudden, these blocks started falling. It was like a thud, thud."
Ed Fisher, a government worker, said some of the marble pieces shattered, spraying the terrace four floors below the pediment with smaller chunks of stone. A group of students from Columbus, Ohio, tried to pocket some of the fragments as souvenirs, Fisher said.
"A few of us attempted to. The police officers were like 'you have to put that back,"' said Sarah Rosenblum, 13, a member of the 8th grade class.
A short time later, workers loaded the roughly 40 pieces into plastic fruit crates and carried them away. Architects estimated a 12 inch by 10 inch piece broke off from the pediment, Court spokeswoman Kathy Arberg said.
A structural engineer and photographer from the Architect of the Capitol's office planned to use a lift to inspect the pediment, Arberg said.
Officials with the Office of the Architect of the Capitol conducted a routine check of the pediment two years ago and found no indications of problems, spokeswoman Eva Malecki said.
The weight of the chunk was not immediately available. However, a cubic foot of Vermont marble weighs 172 pounds, said Robert Pye, director of the Vermont Marble Museum in Proctor, Vt.
Earlier in the morning, dozens of people had lined up in hopes of getting a seat for arguments inside the court — a practice that is not unusual. Justices were back on the bench Monday following a two-week recess.
The fallen marble lay directly in the center of the path up to the court entrance.