A lustrous gathering

Keep collecting minerals, and after a while you start completing sets. I looked around my hoard not long ago and found examples of all the major mineral luster classes. So here's a set in the gallery of mineral lusters, ranging from metallic to dull.

One of the lusters is problematic for me, though: the ultra-glassy, nearly metallic glitter called adamantine luster. It's like the color indigo in the rainbow—is it really there, and if so, is it really useful? I'd feel that way even if I could photograph it, which I can't. Very few minerals display it, and it isn't diagnostic for any of those. Nevertheless, all the authorities mention adamantine luster, and so do I.
_{Metallic luster of chalcopyrite — Geology Guide photo}