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Aon Center

The Aon Center is the third-tallest building in Chicago. It was completed in 1973 and was originally named the Standard Oil Building. When it was completed, the building was a visual wonder to behold, thanks to the decision to sheath the entire structure in Italian Carrara marble. The building looked great, but its fetching exterior came at a very high price.

Carrara marble is much thinner than building materials normally used to clad buildings, and in 1974 one of the slabs detached from the building and crashed into the roof of the neighboring Prudential Center. An investigation revealed the completely unsuitable marble was cracking and bowing all over the exterior. Ultimately, the building was refaced with granite at a cost of more than $80 million.

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