The term Seafoam Turquoise does not refer to a mine or location where certain turquoise is found.
Rather it refers to two visual characteristics that turquoise nuggets might have. The turquoise could come from any number of mines.
Seafoam refers to both color and shape.
Here is a slide show with examples of the color seafoam, used to describe interior paint, linens and clothing among other things. Although the colors vary, you can see the sea in all of them!
Below is what the shape of seafoam can look like, but it varies considerably. It is meant to look like the configuration of bubbling foam at the seaside, so bumpy turquoise in the seafoam color.
For beads, the nuggets are not cut, but left in their natural shape.
If to be mounted such as on the vintage necklace below, the back of the seafoam nugget is flattened but the top is left bumpy.