Levi's rivets are made of copper. They are specifically designed to reinforce points of stress on the jeans, like the pockets.
The copper rivets are a crucial part of the original design of Levi's blue jeans (originally work pants) and were patented by Levi Strauss & Co. and Jacob Davis on May 20, 1873. The placement and material of the rivets contribute significantly to the durability and longevity of the jeans.