Ludwigite and yuanfuliite from fumarolic exhalations of the Tolbachik volcano (Kamchatka, Russia)
Bulakh M. O., Pekov I. V., Koshlyakova N. N., Sidorov E. G.
Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2021. V. 150. N 6. P. 67-87
The paper displays data on ludwigite and yuanfuliite of new fumarolic genetic type. Both these ferric-magnesian borates (oxoborates) have been found in exhalations of the Arsenatnaya fumarole at Tolbachik volcano, Kamchatka. They occur in mineral assemblages formed at temperatures above 550°С. Ludwigite is mainly associated with anhydrite, diopside, minerals of the berzeliite–schäferite series (garnet supergroup), tilasite, svabite, calciojohillerite, hematite and rhabdoborite-group minerals, whereas yuanfuliite occurs with hematite, forsterite, enstatite, diopside, fluorophlogopite, magnesioferrite and spinel. The replacement of ludwigite by yuanfuliite was observed. Both oxoborates are represented by previously unknown chemical varieties, almost free from Fe2+, Al and Ti admixtures. Ludwigite is enriched in Mn3+, up to the composition (Mg2.05Cu0.01)2.06(Fe3+0.71Mn3+0.29Cr0.01)1.01[B0.96O3]O2. Yuanfuliite is chemically very close to the ferric end-member of the warwickite–yuanfuliite series and contains only a small amount of Sn admixture; its typical composition is Mg1.10Fe3+0.91Sn0.03[B0.98O3]O. Their orthorhombic unit-cell parameters are as following: a = 9.297(6), b = 12.349(7), c = = 3.021(2) Å, V = 346.5(4) Å3 for ludwigite; a = 9.30(4), b = 9.43(3), c = 3.051(13) Å, V = = 268(2) Å3 for yuanfuliite. Raman spectra of ludwigite with different contents of admixtures, of yuanfuliite and warwickite, are given and discussed.
Keywords: ludwigite, yuanfuliite, ferric-magnesian oxoborate, Raman spectrum, fumarole, Tolbachik volcano, Kamchatka