Muonionalusta is a fine octahedrite - iron-nickel - around 4.54 billion years old. The slices show the Widmanstätten pattern very clearly - iron crystals formed in a vaccuum marking distinctive, angular structures. It fell about 110 thousand years ago and was found in 1909. These pieces are found by some friends of mine who spend a large part of their year traipsing around the forests with huge metal detectors. Apparently there are far more mosquitoes than you'd imagine.
Roughly rectangular, around 4x2.5cm.