built in 1973 AON center was once the tallset building in chicago.
it is the 4th tallest in the US and 16th tallest in the world.
the buildings facade is made of mount airy white granite.
it was once made of marble but was refaced for about $80 million dollers which was over half the cost of the building itself. the old marble was crushed and used for landscaping.
those facts are from: Aon Center (Chicago) - Wikipedia, the free encyclopedia
this pic is from www.skyscraperpicture.com/aoncenter.htm