This piece of petrified will always be one of my favorites as it is the first ever 'round' I found. A round being a complete branch or trunk which shows the concentric growth rings.
It was found in the Conway river on the South Island of New Zealand, just after some heavy rains. It has beautiful, well defined growth rings and is possibly from the Araucariaceae family of trees.
Watch it being found on YouTube
Age: ~80 million years old (Cretaceous)
Location: South Island, New Zealand
Size: 6cm long, 5cm wide, 9cm high (2.4" x 2" x 3.5")
Weight: 255g (0.5lbs)