Jonesite
A barium-potassium titanium aluminosilicate named for Berkeley microscopist Francis Tucker Jones.
Intro adapted from Wikipedia (CC BY-SA).
Jonesite is an IMA-recognized mineral species in the silicate class, with the chemical formula KBa₂Ti₂(Si₅Al)O₁₈·nH₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/m).
Key properties: Mohs hardness 3–4; specific gravity 3.25; refractive index 1.66; optically biaxial.
IMA symbol Jon, IMA status: approved, named in 1976.
Found in fractures and cavities of brecciated greenstone enclosed in blueschist.
It is found associated with Neptunite, benitoite, joaquinite, natrolite.
The name refers to Francis Tucker Jones (1905-1993), Research Chemical Microscopist of Berkeley, California, USA, who discovered the mineral.