CINCINNATI – The coin world is abuzz over the auction of a rare silver dollar, one of the most valuable in the world and one of only 15 known to exist from a never-circulated group made for the likes of the King of Siam and the Sultan of Muscat. The 1804 Adams-Carter silver dollar fetched more than $2 million in a private sale two years ago and is expected to top that again this week. The coin has been owned by a Boston banker, a Texas publishing mogul and by a collector who sold everything to help build a church school in Ohio. The auction is a major happening for collectors – even ones who can’t afford the expected price tag – partly because it will be a rare opportunity to see the coin. It’s the highlight of the Central States Numismatic Society Convention that runs today through Saturday in Cincinnati. Anyone registered to bid on any item in the auction may view the coin, and that could number in the thousands, said Todd Imhof of Heritage Auction Galleries of Dallas. Joe Barrett, co-owner of three Rare Coin Gallery shops in the Cincinnati area, compared the convention to a movie buff’s visit to a film museum, with Kevin Costner as tour guide. ‘For coin people, it doesn’t get any better than this,’ Barrett said. ‘For young collectors, this is an opportunity to see things they wouldn’t get a chance to see otherwise.’ Beth Deisher, editor of Coin World magazine, suggested the valuable coin may not be seen in public for another 50 years. ‘It’s a rare coin that has a great story,’ she said. Coin Values magazine rates the 1804 Adams-Carter silver dollar as the seventh most valuable coin in the world. The most valuable is a 1933 $20 double eagle that sold for $7.6 million in 2002. Only 15 of the 1804 silver dollars are known to have been struck, and coin aficionados can account for every one of them. Six are held by museums. The coins were never circulated and weren’t actually struck in 1804 – the date refers to the year after the U.S. Mint stopped making silver dollars. The front of the coin shows a bust of Lady Liberty in profile, the reverse a version of the Great Seal of the United States. Coin Facts says eight of the coins were ordered struck by the U.S. Department of State in 1834 to be given to foreign heads of state, including the King of Siam and the Sultan of Muscat. One specimen was made in 1857. The other six, including the Adams-Carter dollar, were made sometime after that – possibly illegally by a mint employee. The one being auctioned Thursday is named for 19th century collector Phineas Adams, an early owner, and Amon Carter Sr., a later owner, Texas oilman, entrepreneur and publisher of the Fort Worth Star-Telegram. In November 2001, Phillip Flannagan donated the coin to raise money for the building fund at Middletown Christian School, north of Cincinnati. It brought $874,000 at auction. The rest of Flannagan’s collection, totaling some $2 million, went to Grace Baptist Church, which operates the school. The name of the current owner is closely guarded. Heritage Auction Galleries identifies him only as an East Coast collector. The buyer mostly likely will bid through an agent. Internet bidding will continue until two hours before Thursday night’s auction, Imhof said. The high bid on Tuesday had reached $1.7 million. The live auction, expected about 9:30 p.m. EDT Thursday, will be streamed on Heritage’s Web site, Imhof said.