Steedeite
Steedeite is an IMA-recognized mineral species in the silicate class, with the chemical formula NaMn₂[Si₃BO₉](OH)₂.
It crystallizes in the triclinic crystal system (space group P-1).
Key properties: specific gravity 3.106; White streak; Vitreous luster; optically biaxial.
IMA symbol Sed, IMA status: approved, named in 2013.
Precipitated in vugs in altered sodalite syenite by late-stage aqueous fluids, presumably highly alkaline due to the presence of natrite.
It is found associated with Microcline, analcime, nepheline, aegirine, pyrrhotite, sodalite, eudialyte-group minerals, natron, catapleiite.
The mineral was named to honor Anthony Hosford Steede (b. 1940) in recognition of his contributions to the understanding of the mineralogy of Mont Saint-Hilaire.