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Micro-FTIR study of quartz crystals from Zhelannoye deposit, Subpolar Urals

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Shtenberg M.V.1,2, Repina S.A.1

1 Institute of mineralogy UrB RAS; 2 South-Ural State University, Miass, Russia

shtenberg@mineralogy.ru

 

Quartz is the most popular mineral to get the information about conditions of formation. In its composition and structure are showed main stages of geological environment evolution. Quartz crystals are the most informative to trace changes in composition on various zones and sectors of growth. Infrared spectroscopy is an effective method to investigate various hydrogen-bearing groups.

The quartz crystals (citrines, smoke, clear) were collected from Zhelannoye deposit, Subpolar Urals. The double polished sections parallel to (0001) were prepared. We measured unpolarized infrared spectra in the 5500-2000 cm-1 region, using a MultiScope Perkin Elmer FTIR microscope equipped with a MCT detector under the condition of 4 cm-1 resolution at room temperature. All spectra were co-added 128 scans. The measured area was restricted by the 50x50 μm2 square aperture for each spot. Spots were measured along profile line in 1 millimeter.

The absorbance spectra were normalized by thickness of sample. Curve-fitting analysis was carried out by using PeakFit for Windows software. Overlapping absorption bands in each spectrum were resolved into 9 bands, which include Al-OH bands at 3315 cm-1, 3378 cm-1 and 3432 cm-1, Al-O(Li) bands at 3403 cm-1, 3440 cm-1, 3482 cm-1 and 3512 cm-1, and an Si-O bands at 3200 cm-1 and 3300 cm-1 [1]. A Lorentzian function was used as a model of OH bands and Gaussian function for Si-O bands. The basic relationship between IR intensity and concentration was given using Beer-Lambert law. The equation was used [2]:

CH = A·∆, (1)

CH – the H amount in 106 Si; A – the calibration factor; ∆ – the integrated absorbance under the OH band, normalized by the sample thickness. The hydrogen amount was converted in weight-part concentration OH groups.

The zonal structure in weakly colored citrine crystals using binocular microscope was established (fig.). The shadows of the Brazilian growth twins at crystal rim and sericite powder at the upper faces were described. It is supposed, the growth twins and sericite powder were formed as a result of the imposed mechanical strains. The zoning profile was revealed, that the content of Al-O (Li) groups in the crystal rim is less, than in the core part. It is possible to assume, that during the rim crystallization the conditions accompanied with the Li depletion in hydrothermal fluids were changed. Also smoky quartz crystals from this deposit were studied. Similar shadow zone wasn’t observed there and OH-groups location is uniformly from core to rim.

Thus, IR microspectrometry method allows to reveal OH-groups location in different quartz crystal zones and determinate a change the mineral-forming condition changing.

All spectra measurements were executed at “Geoanalyst” Centre in the Institute of Geology and Geochemistry, Urals Branch of Russian Academy of Science. This work is supported by FTP “Scientific and scientific-pedagogical personnel of innovative Russia” (GC № 14.740.11.1212 of 14.06.2011).

 

Fig. The zoning profile of concentration Al-OH and Al-O(Li) groups in citrine.

 

References:

 

1. Kats A. (1962) Hydrogen in Alpha-quartz. Philips Research Reports, 17 201-279.

2. Kronenberg A.K. (1994) Hydrogen speciation and chemical weakening of quartz. Rev. Miner. 29 123-176.
New compounds NaBaM(BO3)2 (M = Sc, Y, Yb, Dy)

 

Svetlyakova T.

V.S. Sobolev Institute of Geology and Mineralogy SB RAS, Novosibirsk, Russia

svetlyakovatn@gmail.com

 

Simple and complex rare earth borate compounds are widely used as laser matrices or non-linear optical materials. The complex rare earth borates with alkali metals, for instance, LnNa3(BO3)2 (Ln = Y, La, Nd, Gd) [1; 2] and Ln2Ba3(BO3)4 (Ln = La, Pr, Gd) [3] are of great interest due to luminescent properties and low concentration quenching of the rare earth ion [4].

In our previous study of the MBO3-BaB2O4-Na2B2O4 (M = Sc, Y) system a chemical reaction between the initial components was found. As a result a new compounds BaNaSc(BO3)2 and BaNaY(BO3)2 were discovered [5]. This suggests the presence of similar compounds with other rare earth elements.

Search of new NaBaLn(BO3)2 compounds (Ln = La-Lu) was done using two-step solid phase synthesis and spontaneous crystallization [6].

 
 

Powder samples of BaNaLn(BO3)2 were prepared by two-step solid phase synthesis. At the first stage the mixture was heated at 800 oC for 16 hours to remove CO2 and H2O. The duration of the process was controlled on the basis of the

Fig. X-ray spectra of the crystal samples of: NaBaDy(BO3)2 (a); NaBaYb(BO3)2 (b); NaBaSc(BO3)2 (c), NaBaY(BO3)2 (d).

loss of initial charge weight. The temperature of the second stage was found with a stepwise 50–70 оС increase of the temperature. After each stage of the heat treatments the X-ray powder diffraction analysis was carried out. After reaching the complete reaction between the components the annealing process was stopped. A criterion for the completion of the process was the absence of signals of admixture phases in the X-ray diffraction patterns of the synthesized powders. The heat treatment at both stages was alternated with careful grinding of intermediate reaction products.

Among the whole range of rare earth elements the X-ray powder diffraction pattern of compounds with ions Yb3+ and Dy3+ contained no lines of famous borates with these elements, and we failed to identify the existing set of peaks.

Search of the solvents for crystal growth was held on the base of experiments with NaBaSc(BO3)2 and NaBaY(BO3)2. The solvents under study are: BaO-B2O3-Na2O (eutectic Е1: 0.56 BaB2O4 - 0.44 NaBO2, melt temperature 826 оС; eutectic Е2: 0.56 NaBO2-0.44 BaNaBO3, 830 оС); NaBO2 (966 оС); 0.39 BaB2O4-0.61 NaF (754 оС). The major parameters for choosing the best solvent was crystal yield coefficient and overall solubility of compound in the system.

The highest yield coefficient of NaBaSc(BO3)2 compound was found for 0.56 BaB2O4-0.44 NaBO2 solvent and equals 2.644. Nevertheless it is difficult to grow NaBaY(BO3)2 crystal in this system because the solubility is less than 5 weight %. Next experiments showed that the most effective solution for crystal growth for both compounds is 0.39 BaB2O4-0.61 NaF system. The yield coefficients are high and the crystallization temperatures of the compounds are rather low. This solution was used for crystal grow of new compounds with ions Yb3+ and Dy3+.

X-ray spectra of the sintered powders of new compounds are in full agreement with that of the single crystals. Fig. (a, b, c, d) demonstrates identical peak locations on X-ray spectra of NaBaSc(BO3)2, NaBaY(BO3)2 and new compounds with Yb3+ and Dy3+ ions. Thus it may be conclude the compositions of new compounds are NaBaYb(BO3)2 and NaBaDy(BO3)2, respectively.

All compounds crystallized in one structural type (.space group) and belong to one family of complex island layered ortoborates [7]. For all studied orthoborates structural characteristics were calculated.

 

References.

 

1. Mascetti J., Vlasse М., Fouassier С. (1981) J. Solid State Chem. 39. 288pp.

2. Zhang Y, Chen X.L, Liang J.K, Xu T. (2002) J. of Alloys and Compounds. 333. 72pp.

3. Palkina K.K., Kuznetsov V.G., Dzhurinskii B.F., Moruga L.G. (1972) Russ. Inorg. Chem. 1972. V. 17. 341pp.

4. Blasse G., Bril A. (1967) J. Inorganic. Nucl. Chem. 29. 266pp.

5. Svetlyakova T.N., Kononova N.G., Kokh A.E., Kokh K.A., Pal’chik N.A. (2011) Russ. J. Inorg. Chem. 56. No 1. 117-121pp.

6. Svetlyakova T., Kokh A., Kononova N. (2011) The materials of XVII International congress “Crystal Chemistry, XRD and Spectroscopy”. St.Petersburg, 151-152pp.

7. Seryotkin Y., Bakakin V., Kokh A., Kononova G., Svetlyakova T., Kokh K., Drebushchak T. (2010) Journal of Solid State Chem. 183. № 5. 1200-1204pp.

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