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hercynite

hercynite Min.
  (ˈhɜːsɪnaɪt)
  Also hercin-, hyrcin-.
  [Named (1839) Hercynit, f. L. Hercynia (see Hercynian a.).]
  Aluminate of iron, found in black octahedral crystals in the Bohemian Forest.

1849 J. Nicol Min. 251 Hercynite. 1887 Dana Man. Min. 215 Hercynite, a spinel affording on analysis alumina and iron protoxide, with only 2·9 per cent. of magnesia.

Oxford English Dictionary

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