In one of the most expensive purchases ever by the Smithsonian Institution's Museum of American History, it has bought a "sunstone" from the abandoned and destroyed Nauvoo temple for $100,000.

"It's one of the largest expenditures this museum ever made," said Richard Ahlborn, curator in the museum's division of community life. "That's because we're a history museum and artifacts usually don't cost that much. Art museums spend many times that amount, but we don't. In fact, the board of regents of the Smithsonian had to approve it."The museum sought the piece because "it is a central symbol of the heroic effort by the Mormon pioneers in their movement from upstate New York to Utah to maintain their belief system," Ahlborn explained.

"Nauvoo was the mid-point of that migration," noted Ahlborn. "In Nauvoo, it seemed for a while that the Church could establish itself on a permanent basis. But Joseph Smith was killed and Brigham Young led the Church to Utah."

He added, "Few religions have their beginnings in America. That alone is quite a phenomenon, not to mention the strength and growth the Mormon Church has shown. The stone is symbolic of the most persistent religious movement in American history."

The 2 1/2-ton stone, with a carved radiant face emerging between cloud banks beneath a pair of hand-held trumpets, was put on display just a few feet to the side of the original Star Spangled Banner at the museum's main entrance.

"Except for the Star Spangled Banner, you couldn't ask for a more central location," said Ahlborn. That also means the stone will be a keystone display, so to speak, during special museum events planned through 1992 to mark the 500th anniversary of the voyage of Columbus. "We get 5 million visitors a year even without special events," Ahlborn said.

The museum has its stone sitting on a pedestal eight feet high, "so visitors look up at it like they would have at the temple," Ahlborn said. The display also includes pictures and architects' drawings of the temple, and a brief history of the stone and the pioneers.

Ahlborn said the stone - only one of two complete sunstones known of by the Smithsonian - had been owned for the past 75 years by the Historical Society of Quincy and Adams Counties in Illinois, and had been displayed on the grounds of the governor's mansion in Quincy. However, the society decided to sell it to raise money, Ahlborn said. The other complete sunstone is displayed in the Illinois State Park in Nauvoo.

The Nauvoo Temple, completed in 1845, originally had 30 sunstones. Limestone pilasters - or square columns - around the exterior of the temple had moonstones decorating their base and were capped by sunstones. Starstones were carved above the sunstones.

The Mormons abandoned the temple when they were forced out of Illinois by mobs and migrated to Utah. The temple was burned in an 1848 fire and later destroyed by a tornado. Some of the temple stones were used by later Nauvoo settlers in construction of nearby homes.