zircon-earthhttp://www.oed.com/dictionary/zircon-earth_n%3Ftab%3Dmeaning_and_usezircon earth, n.
Revised 2021

zircon earthnoun

Now historical and rare. Mineralogy.
  1. 1794–
    Zirconia (zirconium dioxide).
    1. 1794
      The other three [earths], as the adamantine spar earth, circon earth, and australis, have not been yet applied to any useful purposes.
      J. G. Schmeisser, System of Mineralogy vol. I. 37
    2. 1912
      The zircon earth is in the trade in the powdered form.
      Mineral Industry vol. 20 543
    3. 2009
      Klaproth first named the new element Zirkonerde (zircon earth, or zirconia).
      G. Roza, Zirconium i. 8

Originally published as part of the entry for zircon, n.

zircon, n. was revised in March 2021.