Lucky nut
This is a Walnut I found some while back. It has a shell that is made out of three parts instead of two.
This is far more seldom than a four leafed clover. According to the internet a four leafed clover has an occurence of roughly 1 in 5,000 to 10,000 while the three shelled wallnut is 1 in 150,000 to 200,000 nuts.
