Natural pseudowollastonite: Crystal structure, associated minerals, and geological context

摘要: Abstract Pseudowollastonite, an extremely rare constituent of ultrahigh-temperature combustion metamorphic and igneous rocks, has been found as a rock-forming mineral in Ca-rich paralava veins Nabi Musa fossil mud volcano (Dead Sea area). Pseudowollastonite-bearing paralavas are the products metamorphism associated with spontaneous burning methane. The melt began to crystallize at 1480–1500 °C about ambient pressure. Pseudowollastonite enters two assemblages: (1) rankinite, larnite, nagelschmidtite, wollastonite (1 T ), gehlenite-rich melilite, Ti-rich andradite, cuspidine, fluorapatite; (2) parawollastonite (2 M fluorellestadite. In this study we present first single-crystal structure determination natural pseudowollastonite. from dome is stoichiometric CaSiO 3 belongs most widespread four-layer polytype:  = 6.83556(10) A, b  = 11.86962(18) c  = 19.6255(3) β  = 90.6805(13)°, V  = 1592.21(4) A , space group C 2/ . We argue that pseudowollastonite so scarce nature because its formation requires joint action several uncommon factors: availability hot melts T > 1200 °C bear free calcium but poor Mg Fe (mostly 3 + ) their crystallization shallow crust followed by quenching.