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Crystal Structure and Chemical Composition of Ludwigite from Vranovac Ore Deposit (Boranja Mountain,Serbia)

Acta Geologica Sinica(English Edition) 2012年第6期86卷 1524-1538页

作者： pavle tancic Radovan DIMITRIJEVIC Maja POZNANOVIC Aleksandar PACEVSKI Slobodanka SUDAR Geological Institute of Serbia Faculty of Mining and Geology Department of Mineralogy and Crystallography

The crystal structure of ludwigite from Vranovac ore deposit （Boranja Mt., Serbia） was refined using the X-ray powder diffraction （XRPD） Rietveld method in the space group Pbam to a final RB=7.45% and RF=5.26%. It has the unit cell dimensions of： a=9.2515（2） A; b=12.3109（2） A; c=3.03712 （7） A; and V=345.91（1） A3. The calculated distances and angles are mostly in good agreement with the Mg2＋-Fe2＋ substitutions across the M（1） and M（3） sites, as well as with the Fe3＋-AI3＋ replacement in the M（4） site. However, the mean observed M（2）-O distance is considerably shorter than prescribed, due to a slight increase of the Fe3＋ content in the M（2） site. Such replacement was compensated by slight increase of the Fe2＋ content in the M（4） site, resulting in the （Mg1.4sFe2＋o.46Fe3＋***.o2）2.o1 （Fe3＋o.94Fe2＋0.04Al0.02）1.00B1.00Os composition. The formation temperature was estimated to be about 500- 600C. The influences of the various chemical compositions to the crystallographic parameters, M-O distances, M（3） and M（4） sites shift, distortion parameters and estimated valences, were also studied and compared with other reference samples.

关键词： ludwigite crystal structure chemical composition M-O distances distortion parameters,ions valences comparison formation temperature

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Macroscopically-Zoned Grandite from the Garnetite Skarn of Meka Presedla(Kopaonik Mountain,Serbia)

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Acta Geologica Sinica(English Edition) 2012年第2期86卷 393-406页

作者： pavle tancic Predrag VULIC Reinhard KAINDL Bernhard SARTORY Radovan DIMITRIJEVIC Geological Institute of Serbia BelgradeSerbia Department of Crystallography Faculty of Mining and GeologyUniversity of BelgradeBelgradeSerbia 3 Institute of Mineralogy and Petrography University of InnsbruckInnsbruckAustria

The macroscopically-zoned grandite from the garnetite skarn of Meka Presedla （Kopaonik Mountain, Serbia） was studied with optical microscopy, electron microprobe analysis （EMPA）, Fourier transform infra-red （FT-IR）, and Raman methods. The EMPA results indicate that the main core-rim compositional variations （Ca2.93-2.97Mn0.05-0.06Mg0.00-0.01AI1.14-L26 Fe0.72-0.83 Ti0.00-0.02Si2.97-3.02012） slightly differ along the zones, showing evidence for a quasi-cyclic alternation of the oscillatory zoning nature. Among this, considerable variation is observed only by the AI-Fe3＋ substitutions in the octahedral site. The EMPA also indicate that the grandite zones compositionally vary, mostly within ＋1 and ±2 mol% of the homogeneity level range, that is, Grs64±1Adra36±1SpS2 （A）, Grs62±1Adra38±1Sps2 （B）, Grs59±2Adr40±2Sps2 （C）, Grs58±2Adr41±2Sps2 （D）, and Grss±1Adr41±1Sps2 （E）. Therefore, the investigated garnet can be considered as relatively highly homogeneous. The majority of compositions lie within the narrow miscibility region of 0.58±2〈XGrs〈0.64±1, without gaps, and with only three outliers near the zone boundaries of approximately 0.38〈XGrs〈0.52. FT-IR and Raman bands are almost constant within the zones and adequate to the chemical compositions. All of the zones should be considered as anhydrous. From the results, formation temperatures between -600 and 720℃ and pressures 0f-2-3 kbars, are derived. Among five possible causes for the slightly optical anisotropy of grandite, three were reconsidered, and consequently rejected.

关键词： grandite anisotropy compositional variation zone homogeneities miscibility region

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