Manganrockbridgeite from the Jocão claim, Conselheiro Pena, Minas Gerais, Brazil: chemistry, spectroscopic and structural data

The world's second occurrence of the recently described manganrockbridgeite was found in a mineral assemblage in the Joco (Cigana) pegmatite, Conselheiro Pena district, Minas Gerais (Brazil).Manganrockbridgeite forms green botryoidal--crystalline crusts with a velvety surface covering the walls of leached cavities in triphylite replaced by correianevesite and Mn-rich vivianite.The outer zone is significantly richer in Mn than the inner zone where the manganrockbridgeite passes to frondelite.Other associated minerals are hureaulite and kenngottite-like phosphate.Empirical formulae based on EPMA, Mssbauer and XPS spectroscopy are (Mn 1.36 Fe 2+ 0.46 Fe 3+ 0.09 Ca 0.03 Mg 0.01 0.05 ) 2.00 Fe 3+ 2.95 (PO 4 ) 3.00 (OH) 3.84 (H 2 O) 1.16 for the outer zone and (Mn 1.03 Fe 2+ 0.49 Fe 3+ 0.29 Ca 0.03 Mg 0.02 0.14 ) 2.00 Fe 3+ 2.94(PO 4 ) 3.00 (OH) 3.81 (H 2 O) 1.19 for the inner zone of aggregates.Raman spectra and assignment of individual decomposed bands to vibrational modes show a good agreement with data published for frondelite from the Joco locality.Powder diffraction data of the studied manganrockbridgeite correspond to the type material from Hagendorf-Sd, Germany.Unit-cell parameters for space group P2 1 /m are a = 5.195(2) , b = 16.936(4), c = 7.452(2) , = 110.25(3)and V = 615.1(4) 3 .