Glass-like allotropes

Last year I mentioned that I was intrigued by the idea of basing one's year around the atomic number that corresponds to one's age.

Well, I have reached the last day of my Selenium Year, and let me tell you: I really seleniumed it up.

Selenium

In the past year, I made a concerted effort to connect my life to selenium:

• I, like selenium, rarely occur naturally in my elemental state.
• As some can affirm, I, like selenium, am toxic in large doses. On the flipside, deficiency of me, though rare, can be fatal.
• While I tried to form the active center of the enzymes glutathione peroxidase and thioredoxin reductase, as selenium does, I was only partially successful in this endeavor.
• Like selenium, I have a lighter cousin named Sulfur.
• I worked most of year to develop six isotopes, and by November I was up to five. But finally last week I formed my sixth and final isotope. So, success!
  
• For a brief period early last year, my primary use was as a photoconductor in plain paper copiers.
• I spent most of July as a black glass-like allotrope.