Wiktionary
hercynite
n. (context mineral English) An isometric-hexoctahedral black mineral containing aluminum, iron, and oxygen.
Wikipedia
Hercynite
Hercynite is a spinel mineral with the formula FeAlO.
It occurs in high-grade metamorphosed iron rich argillaceous sediments as well as in mafic and ultramafic igneous rocks. Due to its hardness it also is found in placers.
It was first described in 1847 and its name originates from the Latin name for the Harz, Silva Hercynia, where the species was first found.
Hercynite is a spinel of regular symmetry and normal cation distribution, but some disorder occurs in its structure. It consists of ferrous (Fe2+) ions and aluminium ions, however some Fe3+ may be located in the structure of hercynite.