[Greg McKaskle]

Since you are into building cool optical tools, may I suggest building one which will let you view it through a polarized filter illuminated with polarized light. I believe this referred to as polarized microscopy.

I haven't build one myself, but I suggest it because the shiny side in the second photo seems to have circular striations. To me that looks like it is due to cooling on a casting. There are also a distinctive dark mark at the root which looks like a surface abrasion due to forceful clamping or extraction of some supporting surface.

Cool riddle.

Greg McKaskle