I'm not sure what these were made for, but they are rather nice, a bit like single crystal silicon boule slices except made of germanium instead. I got them from a guy I bought a batch of germanium lenses from (see above): He thought I would appreciate them, and I do!
Source: eBay seller 142pimp
Contributor: eBay seller 142pimp
Acquired: 16 November, 2003