Celadonite, the 10-Å green clay mineral of the manganese carbonate ore, Úrkút, Hungary
Reference:
Acta Mineralogica-Petrographica, Szeged 2004, Vol. 45/1, pp. 65–80
Szerző:
Tamás G. Weiszburg
Erzsébet Tóth
Anton Bertan
Abstract:
The current study is a detailed mineralogical description of the colour-giving green clay mineral of the Liassic manganese carbonate ore of The current study is a detailed mineralogical description of the colour-giving green clay mineral of the Liassic manganese carbonate ore of Úrkút, Transdanubian Central Range, Hungary. Pure sample was obtained by a three-step separation procedure, designed in particular for the mixed clay-sized material of the manganese carbonate ore. Full chemical analysis (ICP-AES), Fourier-transform infrared spectroscopy (FTIR), X-ray powder diffraction (XPD) and TEM studies were carried out on the green layer silicate.
The bluish-green layer silicate occurs as euhedral laths. The crystals have a characteristic size range: 0.1–2.1 µm in length and 0.07–1.14 µm in width. The structure is a TOT mica structure, smectite interlayering has not been observed. The chemical formula (K0.87Na0.03)(Fe3+0.90Mg0.71Al0.22Fe2+0.14Mn2+0.02Ti0.00)(Si3.97Al0.03O10)(OH)2 reveals an Fe3+-rich dioctahedral mica. Based on the chemical composition, the studied mineral is classified as celadonite in either of the three latest classification schemes (Rieder et al., 1998; Bailey, 1986; Bailey, 1980). The infrared spectrum is characterised by sharp, distinct peaks in the 3400–3700 cm–1 range, revealing a well-ordered structure. The pattern is typical of celadonite as defined by Bailey (1980). The d060 spacing equals 1.510(1) Å, placing the mineral on the celadonite-glauconite boundary (as defined by Bailey, 1980, based on Buckley et al., 1978). The shape and the 1M structure of the crystals indicate that the mineral was formed by primary precipitation.
Though the formation of celadonite is generally associated with submarine basaltic volcanism (Odin et al., 1988), the geological environment of the Úrkút celadonite is essentially sedimentary. Volcanic rocks (of any kind) are unknown in the area and only indirect indications exist for submarine volcanic activity. Thus the presence of celadonite in the ore (as opposed to glauconite or green smectite, suggested by earlier papers) might be a new indicator of the Early Jurassic volcanism contributing to the genesis of the Úrkút manganese deposit. Based on the Úrkút occurrence, the genetic model of celadonite may need to be generalised in the future, with volcanism still playing an important role.
Key
acta2004, celadonite, manganese carbonate ore, Toarcian anoxic event, Transdanubian Central Range, Úrkút, volcanism
