selenite

noun2

1. •
   A soft, glassy form of gypsum (chemical formula CaSO₄·2H₂O).

   • I followed them to my study, and found lying on my writing-table still, with the selenite paper-weight upon it, the sheet of work I had left on the afternoon of the opening of the cylinder. — 1898
2. •
   The anion SeO₃²⁻ derived from selenous acid; any salt or ester of selenous acid.