These are key words: Melanin is not a mineral. Melanin was something used to describe a biological function (elemental). When we break it down into chemistry
Doctor Sebi is talking from a biochemical level as, and he is right, melanin is not an element, but is a molecule made up of different elements or levels of hydrogen atoms. Its not to say that melanin doesn't exist. Its like the concept of a bee by itself being dumb and useless, but when it comes together a whole (melanin) it functions as a whole.
When you get these proponents of melanin come together (carbon, hydrogen, nitrogen, etc) they form that molecule and work as one. This is what I have come up with from my studies, so it may be wrong.