Before the era of plastic, freshwater mussels were the material of choice for the global button industry.
The inside wall of a freshwater mussel’s shell can range in color from pure white to shimmering lavenders and iridescent purples.
European settlers were thrilled to find an abundance of button-worthy mussels in the Great Lakes.
Great Lakes Now
https://www.greatlakesnow.org/2021/08/shell-middens-mussels-muskrats/