What is that?

What is that?  It's the tiny Phillips-head screw in the hinge of my eyeglasses.  I noticed the white color and put it under the microscope to see what that came from.  I think it's soap – I wash my glasses daily when I take a shower, using ordinary soap and water.  I suspect it doesn't all rinse out of that tiny little screw head, especially with the (very) soft water we have in our Utah home.

This photo was taken at 60x with oblique lighting.  It certainly doesn't look here like it looks to my naked eye!