The diamond is worth a whole $15 because it's so big. I wouldn't have paid that much for it, though, because it has the annoying property of looking completely different when the lighting changes, as in panel four above.

I have a new favorite Wikipedia quote: Finally, there is a complex bit of business involving the knocking off, dropping, picking up and exchanging of hats. Determining the source of this quote is left as an easy exercise for the reader. Attempting to compose a quote which further drops the ball on conveying anything important about the subject, while still being entirely accurate, is left as an exercise in futility.