White crystals of the very rare Ba zeolite mineral martinandresite (IMA 2017-038) from the type and only known locality worldwide: Isenwegg, Wasen Alp, Simplon Pass, Brig, Wallis, Switzerland. Type material from the original find in 1989. — Photo: David Hospital · CC BY-SA 4.0
Martinandresite
Martinandresite is an IMA-recognized mineral species in the silicate class, with the chemical formula Ba₂(Al₄Si₁₂O₃₂)·10H₂O.
It crystallizes in the orthorhombic crystal system (space group Pmmn).
Key properties: Mohs hardness 4.5; specific gravity 2.482; White streak; Vitreous to porcelaneous luster; optically biaxial.
IMA symbol Mad, IMA status: approved, named in 2017.
Found in quartz veins cutting zoisite-, celsian-, and armenite-bearing gneiss.
It is found associated with Armenite, quartz, dickite, chlorite.
The mineral was named to honor Martin Andres (b. 1965), the Swiss mineral collector and amateur mineralogist, who discovered the armenite vein locality of Wasenalp.