Demagistrisite
Demagistrisite is an IMA-recognized mineral species in the silicate class, with the chemical formula BaCa₂Mn³⁺₄(Si₃O₁₀)(Si₂O₇)(OH)₄·3H₂O.
It crystallizes in the orthorhombic crystal system (space group Amm2).
Key properties: Mohs hardness 3.5; specific gravity 3.525; Beige streak; Vitreous luster; optically biaxial.
IMA symbol Dmg, IMA status: approved, named in 2018.
Found in rhythmically interlayered braunite-bearing metasediments and hematite-rich cherts formed as sedimentary-diagenetic deposits and that were re-equilibrated under prehnite-pumpellyite facies conditions.
It is found associated with Cerchiaraite-(Mn), namansilite, noelbensonite, orientite, richterite, ruizite, saponite, braunite, calcite, cryptomelane, orthoclase, quartz.
The mineral was named to honor Leandro de Magistris (1906-1990), a leading Italian mineral collector from the 1940s through the 1980s and an expert on the mineral localities of Liguria.