Titre du document / Document title

Ribbeite and alleghanyite from yuzhno-faisulinskoye manganese ore deposit (the South Urals)

Auteur(s) / Author(s)

BRUSNITSYN A. I. ; CHUKANOV N. V. ;

Résumé / Abstract

The rare Mn-silicates - ribbeite and alleghanyite (polymorphic modifications of the Mn⁵(Sio⁴)²(OH)² compound) have been discovered in manganese rocks of the Yuzhno-Faisulinskoye Mn-ore deposit. For ribbeite it is the first finding in Russia. The deposit is an example of the low-metamorphosed volcano-sedimentary oxide-carbonate-silicate type. Manganese ores form there a lens-shaped body occurring between jaspers and siliceous aleurolites. Ribbeite is one of the main minerals in these ores, and alleghanyite occurs among accessories. Both minerals are associated with hausmanite, rhodochrosite, tephroite, caryopilite. They form isometric micrograins (0.01-0.03 mm in size) combined in globular, cockade or flaky aggregates similar to structures of a gel recrystallization. Phisical properties of the minerals are nearly the same: color is light brown in samples, in thin section - pale pinkish-brown or colorless; n^m = 1.75, n^g-n^p = 0.035. Calculated density makes 4.00 and 3.97 g/cm₃ for ribbeite and alleghanyite, respectively. IR-spectra of the minerals has the following absorption bands (cm-₁): 1) rebbeite - 454, 502, 555, 580, 866, 894, 957, 1033, 3295, 3330, 3470 h 3625; 2) alleghanyite - 456, 498, 570, 674, 819, 866, 958, 3355 h 3470. Their chemical compositions correspond to crystallochemical formulas: ribbeite - (Mn^4.91Mg^0.06Al^0.02Fe^0.01)5.00 . (Si^2.00O^8.00)(OH)2.00 alleghanyite (Mn^4.86Mg^0.09Al^0.01)^4.96(Si^2.01O^8.00)(OH)^2.00 Comparison of the minerals density and estimation of the formation PT-conditions for their deposits over the world show that: 1) formation of ribbeite or alleghanyite does not depend on chemical composition of the environment, it was defined mainly by temperature and pressure of the Mn-rocks metamorphism; 2) stability field of rebbeite corresponds to the lower temperatures, the field of alleghanyite - to the higher temperature range. The existence of the both modifications in one rock means that replacement of ribbeite by alleghanyite had started under gradually increasing temperature but was not finished.

Revue / Journal Title

Zapiski Vserossijskogo mineralogičeskogo obŝestva   ISSN 0869-6055 

Source / Source

2002, vol. 131, n^o5, pp. 98-111 [14 page(s) (article)]

Langue / Language

Russe

Editeur / Publisher

Nauka, Sankt-Peterburg, RUSSIE, FEDERATION DE  (1992) (Revue)

Localisation / Location

INIST-CNRS, Cote INIST : 4673, 35400010996677.0090