Oneillite
A rare eudialyte-group mineral rich in manganese and iron, with cyclic silicate rings.
Intro adapted from Wikipedia (CC BY-SA).
Oneillite is an IMA-recognized mineral species in the silicate class, with the chemical formula Na₁₅Ca₃Mn₃Fe₃Zr₃Nb(Si₂₅O₇₃)(O,OH,H₂O)₃(OH,Cl)₂.
It crystallizes in the hexagonal crystal system (space group R3). It is a member of the Eudialyte structural group.
Key properties: Mohs hardness 5–6; specific gravity 3.2; White streak; Vitreous luster; refractive index 1.645; optically uniaxial.
IMA symbol One, IMA status: approved, named in 1998.
Along the contact between a vein of albite and its host nepheline syenite in an alkaline intrusive complex.
It is found associated with Albite, sodalite, pyrite, aegirine.
The mineral was named to honor John J. O’Neill (1886-1966) of McGill University, who was the first to describe the geology of Mont Saint-Hilaire.