An Aluminum–Magnesium Variety of Caryopilite from Goethite–Neotocite–Rhodochrosite Ores of the Mazul Manganese Deposit, Krasnoyarsk Krai

A variety of caryopilite enriched in Mg and Al from the goethite–neotocite–rhodochrosite ores of the Mazul manganese deposit in Krasnoyarsk Krai is described. The mineral occurs as sheaf-like and fibrous aggregates of fine-lamellar individuals intimately intergrown with goethite, hematite, rhodochrosite, and neotocite. The optical parameters of caryopilite are: Z = yellow, X = pale yellow, β ≈ 1.60, γ – α ≈ 0.010 – 0.015, and parallel extinction. The average chemical composition corresponds to the empirical formula (Mn1.95Mg1.61$${\text{Fe}}_{{0.63}}^{{2 + }}$$Al0.58◻0.23)5.00[(Si3.88Al0.12)4.00O10](OH)6, where ◻ is vacancy. The unusually high Mg concentration and elevated Al content allow identification of a new aluminum–magnesium variety of caryopilite. It replaces sedimentary neotocite at low temperatures. It is suggested that at increasing temperature this variety of caryopilite loses Mg and Al, which incorporate into Mg–Mn chlorite and spessartine.