Size: width 85 cm, depth 40 cm, height 55 cm
The big Napoleonite was exhibited in the lobby of Ono City Hall. It was found in Managawa River in 1965, and the discoverer donated it to the city last year. Currently, it is on display at Ono City History Museum.
At any rate, the patterns look unique. I looked at the stone for the first time when I visited the city hall in March this year (2019) and thought it was a fossil of an ancient organism like Fusulina or Trilobite. But in fact, the patterns with circles are the mineral crystals grew in magma. Such a big Napoleonite seems quite unusual.
The stone's official name is spherical diorite and it is designated as a natural monument of Ono City as "Napoleon Stone". The name comes from the fact that Corsica, in which Napoleon was born, is a good producer of the stones. And, Shimowakago district (upstream site of the Managawa River) in Ono City is one of the only four production areas of the stones in Japan.