selenite

Etymology

From Ancient Greek σελήνη (selḗnē, “moon”) + -ite; the chemistry sense comes via the name of the element selenium.

noun

1. (mineralogy) 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, H.G. Wells, The War of the Worlds, London: William Heinemann, page 295
2. (inorganic chemistry) The anion SeO₃²⁻ derived from selenous acid; any salt or ester of selenous acid.