A polyhedron
A polyhedron that has the same combinatorial structure of a icosahedron, though the faces are not equilateral triangles. Image taken from Giovanni StrĂ¼ver's memoir Studi sulla Mineralogia Italiana - Pirite del Piemonte e dell'Elba, from the memories of the Royal Academy of Sciences, Series II, Volume XXVI, 1871.
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From a note of Struver (1871) (3D geometry)