Potassic-hastingsite, KCa 2 (Fe 2+ 4 Fe 3+ )(Si 6 Al 2 )O 22 (OH) 2 , from the Keshiketeng Banner, Inner Mongolia, China: description of the neotype and its implication

Potassic-hastingsite (IMA2018–160), ideally KCa 2 (Fe 2+ 4 Fe 3+ )(Si 6 Al 2 )O 22 (OH) 2 ,was discovered in Danailingou, Inner Mongolia, China. Potassic-hastingsite is black to dark green with a vitreous luster, brittle with conchoidal fracture. The 110 cleavage is perfect and the calculated density is 3.541 g·cm −3 . It is biaxial negative with α = 1.708 (2), β = 1.716 (3) and γ = 1.718 (3). Combined electron probe,icro-analyser (EPMA) and Mössbauer spectroscopy data yielded 35.02 wt