Light gray diamond- fighter jet style object flying over head at high speed in clear sky about 1 second to cross the sky.During a day ice fishing a few winters back, I was standing around talking with a few friends. It was clear blue and was facing the south on the middle of Rocky Pond. There was snow covering the pond and ground surrounding the pond. As I had been watching planes fly over at there usual flying altitude (30,000ft+) all day, I gazed up to look for some more planes. At I would estimate 15,000-20,000ft I noticed an object which I quickly thought as a plane due to its shape. But the speed which this object was moving there was no way it was a plane. At this distance it would have taken at least 30 seconds to watch a plane fly over and this object flew over from east to west in the southern sky in about 1 second. I caught the glimpse of it after it was half way over the sky. It was a diamond-jet shape but much bigger maybe scaled up to about 5 fighter jets. It was a light gray to silver color but could not get a good idea of any other colors due to the speed it was traveling. The object was seen by at least one other friend maybe two.