ISSN 1075-7015, Geology of Ore Deposits, 2009, Vol. 51, No. 8, pp. 827Ð832. © Pleiades Publishing, Ltd., 2009. Original Russian Text © S.K. Filatov, D.S. Rybin, S.V. Krivovichev, L.P. Vergasova, 2009, published in Zapiski RMO (Proceedings of the Russian Mineralogical Society), 2009, Pt. CXXXVII, No. 1, pp. 136Ð143. MINERALOGICAL CRYSTALLOGRAPHY

Thermal Expansion of New Arsenate , Bradaczekite, NaCu4(AsO4)3, and Urusovite, Cu(AsAlO5) S. K. Filatova, D. S. Rybina, S. V. Krivovicheva, and L. P. Vergasovab a Faculty of Geology, St. Petersburg State University, Universitetskaya nab. 7/9, St. Petersburg, 199034 Russia b Institute of Volcanology, Far East Division, Russian Academy of Sciences, Boulevard Piipa, 9, Petropavlovsk-Kamchatsky, 683006 Russia Received December 19, 2007

Abstract—Thermal behavior of two new exhalation copper-bearing minerals, bradaczekite and urusovite, from the Great Tolbachik Fissure Eruption (1975Ð1976, Kamchatka Peninsula, Russia) has been studied by X-ray thermal analysis within the range 20Ð700°C in air. The following major values of the thermal expansion tensor α α α α α × Ð6° Ð1 μ α ° have been calculated for urusovite: 11 = 10, 22 = b = 7, 33 = 4, V = 21 10 C , = c^ 33 = 49 and α α α × Ð6° Ð1 μ α ° bradaczekite: 11aver = 23, 22 = 8, 33aver = 6 10 C , (c^ 33) = 73 . The sharp anisotropy of thermal deformations of these minerals, absences of phase transitions, and stability of the minerals in the selected tem- perature range corresponding to conditions of their formation and alteration during the posteruption period of the volcanic activity are established. DOI: 10.1134/S1075701509080169

INTRODUCTION established that there is a synthetic analogue, NaCu4(AsO4)3, synthesized by Pertlik (1987) under The Great Tolbachik Fissure Eruption (GTFE 1975Ð hydrothermal conditions. The was named in 1976, Kamchatka Peninsula, Russia) is among the six most honor of Hans Bradazcek, a professor of Free Berlin famous fissure eruptions in human history. In addition, it is one of the most studied eruptions (The Great …, 1984). In University (Filatov et al., 2001). the 30 years since the eruption, posteruption mineral for- Urusovite, Cu(AlAsO5). The mineral is light green, mation has been regularly monitored at the newly formed with adamantine luster; is white; is per- Tolbachik volcanoes. For this time, 30 new minerals have fect parallel to (001). It occurs as clusters of plates been described, among which are a number of arsenates: extending parallel to [001] and intergrown along elon- lammerite, Cu3[(P,As)O4]2; alarsite, AlAsO4; coparsite, gation. The temperature at the sampling locality was Cu4O2[(As,V)O4]Cl, johillerite, Na(Mg,Zn)3Cu(AsO4)3; 400°C. The microhardness VHN is 378 kg/mm2; the urusovite, Cu[AlAsO5]; bradaczekite, NaCu4(AsO4)3; and Mohs hardness is 5. Urusovite is pleochroic in light filatovite, K[(Al,Zn)2(As,Si)2O8]. Except for lammerite and johillerite, the listed mineral species are new. green tints. It was named in honor of Academician V.S. Urusov (Vergasova et al., 2002). Bradaczekite and urusovite examined in this study were found, among products of volcanic exhalations at The crystallochemical and mineralogical character- the second cinder cone of the North break of the GTFE, istics of bradaczekite and urusovite are given in the to be intimately associated with hematite, tenorite, table. orthoclase, johillerite Na(Mg,Zn)3Cu(AsO4)3, pono- marevite K Cu OCl , K Cu O (SO ) MeCl, It can be concluded that bradaczekite and urusovite 4 4 10 4 4 2 4 4 as exhalative minerals are formed at high temperatures sylvite, dolerophanite Cu2OSO4, and euchlorine KNaCu O(SO ) . and occur at high temperatures and atmospheric pres- 3 4 3 sures on cooling volcanoes for a certain time after for- Bradaczekite, NaCu4(AsO4)3. The mineral is dark mation. Therefore, the aim of this article is to study the blue, with adamantine luster; streak ranges from pale thermal behavior of these minerals by X-ray thermal sky blue to white; cleavage is not observed. Bradacze- analysis under conditions close to natural. The occur- kite occurs as clusters of dark blue plates. The mineral rence of such toxic elements as arsenic in the studied is stable in air and almost insoluble in water and alco- minerals attaches special importance to this work. The hol. The calculated density is 4.77(1) g/cm3. Lumines- cence was not displayed in short- or longwave UV probable release of As from the of light. Shortly after discovery of the mineral, it was these minerals and its migration in the biosphere is a subject of doubtless concern. Rybin et al. (2007) and Corresponding author: S.K. Filatov. E-mail: filatov@crystal- Filatov et al. (2007) reported the preliminary results of spb.com this study.

827

828 FILATOV et al.

α × Ð6 × Ð9 × Crystallochemical and mineralogical characteristics of bradacze- follows: a = 8.4 10 + 16.4 10 T (average ° α α × kite and urusovite value in the range 20Ð700 C; a average = 14.0), b = 8.0 Ð6 α × Ð6 × Ð9 × α 10 , c = 13.9 10 + 21.6 10 T ( c aver = 21.2), Parameter Bradaczekite Urusovite Ð6 Ð1 αβ = 6.8 × 10 °C . Chemical formula NaCu4(AsO4)3 Cu(AsAlO5) Comparison of the thermal expansion of bradacze- Symmetry, space Monoclinic, C2/c Monoclinic, P21/c kite along atomic rows make it possible to distinguish group axis c as the direction of the greatest expansion (aver- α × Ð6° Ð1 a (Å) 12.053(2) 7.314(2) age value c = 21.5 10 C ), whereas the expansion along axes a and b is 1.5 and 2.5 times less, respec- b (Å) 12.432(2) 10.223(3) tively. c (Å) 7.2529(13) 5.576(2) The major values of the thermal expansion tensor of β (deg) 117.793 99.79 the mineral reveal a much greater anisotropy of deforma- 3 α × α V (Å ) 961.5(3) 410.9(2) tions: 11 = 16 + 0.02 T (average value 11 average = 23), α = 8, α = Ð1 + 0.02 × T (α = 6) (10Ð6 °CÐ1), Calculated density, 4.77 3.93 μ22 α 33 ° 33 average D , g/cm3 (c ^ 33) = 73 . x α Mohs hardness Ð 5 The volume expansion of the structure V = 23 + × α × Ð6 ° Ð1 0.038 T ( V average = 36 10 C ) is estimated as that Color Dark blue Light green expected for arsenate compounds. Origin Volcanic exhala- Volcanic exhala- The cause of the anisotropic thermal expansion of tion tion bradaczekite can be established from comparison of the α values with the crystal structure of the mineral. Bra- daczekite belongs to the alluaudite, Na[MnFe2(PO4)3], EXPERIMENTAL structural type. In the structure, there are three indepen- The X-ray diffraction patterns of polycrystals were dent Cu2+ atoms. The Cu(1) atom is square-coordinated obtained in air using a DRON-3 diffractometer with a mean bond length of Cu2+–O = 1.91 Å. Cu(2) equipped with a KRV-1100 high-temperature device, and Cu(3) atoms (Fig. 2) exhibit distorted tetrahedral using Cukα radiation, Ni β-filter, and tape recording of coordination due to the JahnÐTeller effect. Two sym- reflections. The temperature range is 20Ð700°C; tem- metrically independent As atoms are tetrahedrally coor- perature step is 40°C. dinated with average As–O bond lengths of 1.69 Å and The dimensions of monoclinic unit cell were deter- 1.70 Å for As(1) and As(2), respectively. The structure mined by the least squares procedure using the Unit is based on a sheet of octahedrons [Cu(2)O6] and Cell program and approximated by equations not [Cu(3)O6] combined with tetrahedrons [As(2)O4] (Fig. higher than of the second order. The thermal expansion 2a). Edge-sharing octahedrons make up zigzag chains, coefficients were calculated with the DTC program; which form a sheet via [As(2)O4] Tetrahedrons. The sheets are linked to a framework via [As(1)O4] tetrahe- patterns were drawn according to the DTP program + (Belousov and Filatov, 2007). drons and [Cu(1)O4] squares. Na cations occupy cages in the framework (Krivovichev et al., 2001). In Fig. 2b, the pattern of coefficients of the thermal RESULTS AND DISCUSSION expansion of bradaczekite is comparable with the crys- No phase transitions were detected for either min- tal structure of this mineral. Four short equatorial bonds 〈 2+ 〉 eral in the temperature range of 20 to 700°C. The Cu ÐOeq = 1.98 (solid lines) and two long apical 〈 2+ 〉 selected range covers typical temperatures of formation bonds Cu ÐOap = 2.49 Å (dashed lines) are distin- and transformation of exhalative minerals at volcanoes. guished for each Cu(2) and Cu(3) octahedrons. It is Heating simulation is appropriate to the results of seen that the longest (and weakest) CuÐO bonds 30-year-regime observations, when local temperature (dashed lines in Fig. 2b) are close in orientation to axis α oscillations of cooling at the cones of the GTFE 11 of the maximal thermal expansion of the structure. reached 400°C (Vergasova et al., 2007). The results of Thus, the anisotropy of thermal deformations of the study of thermal expansion of the minerals are given bradaczekite structure is caused by nonequivalent below. lengths of chemical bonds in octahedrons Cu(2)O6 and Bradaczekite. The temperature-dependent varia- Cu(3)O6 distorted due to the Jahn-Teller effect. tions of monoclinic unit-cell dimensions (Fig. 1a) were Urusovite. In urusovite, the monoclinic unit-cell fitted by polynomials not higher than the second order: dimensions linearly vary with temperature to a first a = 12.049 + 0.104 × 10Ð3 × T + 0.139 × 10Ð6 × T2, b = approximation (Fig. 1b): a = 7.304 + 38 × 10Ð6 × T (Å); 12.418 + 0.129 × 10Ð3 × T, c = 7.251 + 0.099 × 10Ð3 × T + b = 10.169 +69 × 10Ð6 × T (Å); c = 5.575 + 37 × 10Ð6 × 0.075 × 10Ð6 × T2 (Å), β = 117.82 + 0.83 × 10Ð3 × T (Å); β = 99.82 Ð 0.32 × 10Ð3 × T (deg); V = 408.1+ 8.0 × T(deg), V = 959.5 + 24.2 × 10Ð3 × T + 21.1 × 10Ð6 × T2 10Ð3 × T (Å3). The coefficients of thermal expansion are as 3 α α α α × Ð6 ° Ð1 (Å ). The coefficients of thermal expansion along the follows: a = 5.5, b = 6.9, c = 7.2, β = Ð3.0 10 C ; α crystal axes calculated on the basis of these data are as the major values of tensor of thermal expansions are 11

GEOLOGY OF ORE DEPOSITS Vol. 51 No. 8 2009 THERMAL EXPANSION OF NEW ARSENATE MINERALS 829

a, Å 12.20 (a)

12.10 β, deg 12.00 118.50 b, Å 12.50 117.50 12.45 V, Å3 12.40 990 c, Å 7.35 970 7.30

7.25 950 0 200 400 600 800 0 200 400 600 800 T, °C T, °C a, Å (b) 7.34

7.32

7.30 b, Å 10.22 β, deg 10.18 99.9

10.14 99.4 c, Å 5.61 V, Å3 5.59 413

5.57

5.55 407 0 200 400 600 800 0 200 400 600 800 T, °C T, °C

Fig. 1. Unit-cell dimensions of (a) bradaczekite and (b) urusovite versus temperature.

α α α α × Ð6 ° Ð1 μ 3+ 5+ = 10, 22 = b = 7, 33 = 4, V = 21 10 C , = atoms are substituted for Al and As (the total num- α ° c^ 33 = 49 . ber of valences is also 8).

Thus, urusovite exhibits a moderate thermal volume Analogy of the urusovite sheet AlAsO4 with net α × Ð6° Ð1 Si O suggests that the structure is layered. The sheets expansion ( V = 21 10 C ) characteristic of sili- 2 5 cates, aluminosilicates, and their aluminate and arsen- in the layered silicates are usually linked by residual ate analogues. bonds, i.e., atoms of alkaline metals (M+) or water mol- ecules. Therefore, the maximal thermal expansion per- To account for the anisotropic character of thermal pendicular to the sheet is characteristic of them. In deformations of the mineral, consider its crystal struc- urusovite, the sheets are linked by bivalent copper ture. According to the determination of the structure (Fig. 3). The single independent site of Cu atoms is (Krivovichev et al., 2000), the mineral is layered. The coordinated by five O atoms forming a tetragonal pyra- radical of the AlAsO5 sheet is similar to that of tetrahe- mid. Four oxygen atoms are arranged at the bottom of 4+ dral net Si2O5 differing in that two tetravalent Si this pyramid at distances of 1.960–1.975 Å from the

GEOLOGY OF ORE DEPOSITS Vol. 51 No. 8 2009 830 FILATOV et al.

(a) As(2)O Cu(2)O6 Cu(3)O6 a

c

(b) α 11

α 33 a

β Cu2 Cu3

Cu2

Cu3 Cu2 c Cu3 Cu2 Cu3

Fig. 2. (a) Sheet ac and (b) chain of octahedrons [Cu(2)O6] and [Cu(3)O6] in the structure of bradaczekite. Long bonds (JahnÐTeller effect) in octahedrons (CuO6) are shown by dashed lines.

Cu atom, whereas the O atom at the apex of the pyra- of a shear nature (Filatov, 1990). In this case, decrease mid is at a distance of 2.370 Å from the Cu atom (Fila- in abut angle β with increasing temperature should tov et al., 2001). cause expansion of the structure near its bisector and In this case, all five CuÐO bonds participate in inter- compression in the perpendicular direction (Fig. 3). layer interaction, including the four shortest, substan- The general thermal expansion superimposed on these tially covalent bonds in square CuO4. Apparently, just deformations will result in enhanced expansion and these covalent bonds between aluminoarsenate sheets weakened or neutralized compression. Indeed, the real of the urusovite structure prevent maximal thermal pattern of the thermal expansion coefficients of uruso- expansion of the mineral perpendicularly to the sheet, vite is distinguished by such character and orientation as is characteristic of other micaceous minerals. (Fig. 3). At the same time, Fig. 1b demonstrates that the β value of the mineral unit cell decreases from 99.8° to A nonfixed symmetry angle of monoclinic unit cell 99.6° in the temperature range of 20 to 700°C. This tending to right angle indicates a tendency of increasing suggests that the anisotropy of thermal deformations is symmetry of crystals with temperature. About 2/3 of

GEOLOGY OF ORE DEPOSITS Vol. 51 No. 8 2009 THERMAL EXPANSION OF NEW ARSENATE MINERALS 831

(a) (b) α 11 α c b b c 33

β a a

AlO 4 AlAsO5

AsO4

Fig. 3. Structure of urusovite projected on (a) (001) and (b) (010) and pattern of coefficients of thermal expansion. monoclinic crystals behave in such a manner (Filatov with such a framework. Under those conditions, the low et al., 1990). thermal expansion of urusovite looks appropriate. α × The coefficients of thermal expansion of V = 36 10Ð6°CÐ1 and 21 × 10Ð6°CÐ1 of bradaczekite and uruso- CONCLUSIONS vite, respectively, allow us to verify the aforementioned The phase transitions, which can occur in exhalative assumption. The measured α values are typical of minerals at variable temperature during the postmag- arsenates and aluminoarsenates. They may be used as matic period of volcanic activity, were modeled by the thermodynamic characteristics of these minerals. X-ray thermal analysis. It was revealed that both of the The elevated expansion of bradaczekite in comparison + studied arsenate minerals, bradaczekite NaCu4(AsO4)3 with urusovite is explained by univalent Na in the and urusovite Cu(AsAlO5), are stable throughout the structure of bradaczekite, which attenuates chemical temperature range of 20 to 700°C. bonds in the compound and results in elevated thermal The absence of phase transitions is a dull result in expansion. The expansion of urusovite is lower in com- α × Ð6° Ð1 terms of crystal chemistry and physical chemistry, but parison with silicates (average V ~30 10 C ). is undoubtedly important in terms of ecology and envi- The strength properties of urusovite (high hardness ronmental protection. Indeed, in the whole real temper- and low thermal expansion) along with copper as its ature range of the formation and transformation of constituent are attractive for utilization of this mineral. exhalative minerals at volcanoes, arsenic incorporated It is also important that this aluminoarsenate has only into bradaczekite and urusovite is firmly retained in the centrosymmetrical modification in the temperature crystal structure of the minerals and remains nonhaz- range of 20 to 700°C. ardous in such a state to people (primarily for the vol- canologists working close to the localities of arsenate findings) and the environment. ACKNOWLEDGMENTS Thermal deformations of these minerals are sub- This study was partly supported by the Russian stantially anisotropic; anisotropy is significantly con- Foundation for Basic Research (project no. 06-05- trolled by the strength of chemical bonds. In the struc- 64327) and the Ministry of Education and Science ture of bradaczekite, the JahnÐTeller distortion of the (grant no. RNP 2.1.1.3077). octahedral site of copper atoms was the controlling fac- tor that determined anisotropic thermal deformations of REFERENCES the crystal structure. 1. R. I. Belousov and S. K. Filatov, “Algorith for Calculating In contrast, in the case of urusovite, anisotropy of the Thermal Expansion Tensor and Constructing the Thermal thermal expansion of the structure expected due to the Expansion Diagram for Crystals,” Glass Physics and Chem- layered character of T2O5 (T = Al, As) and perfect istry 33 (3), 271Ð275 (2007). cleavage parallel to (100) of the mineral was not dis- 2. S. K. Filatov, High-Temperature Crystal Chemistry played because of linkage of layers by covalent CuÐO (Nedra, Leningrad, 1990) [in Russian]. bonds. In this situation, the crystal structure of uruso- 3. S. K. Filatov, D. S. Rybin, and L. P. Vergasova, “High- vite more likely may be considered a framework com- Temperature Expansion of bradaczekite, NaCu4(AsO4)3,” in posed of apex-sharing running tetrahedrons [AlO4] and Proceedings of International Conference on Crystal Chemis- [AsO4] and strong fivefold polyhedrons [CuO5]. The try and Spectroscopy" (Inst. Geol. Geochem., Ural Division, Mohs hardness of 5 typical of urusovite is consistent Russian Acad. Sci., Yekaterinburg, 2007), pp. 109Ð110.

GEOLOGY OF ORE DEPOSITS Vol. 51 No. 8 2009 832 FILATOV et al.

4. S. K. Filatov, L. P. Vergasova, M. G. Gorskaya, P. C. Burns, 9. F. Perlik, “Hydrothermal Synthesis and Structure of and V. V. Ananiev, “Bradaczekite, NaCu4(AsO4)3, A New Sodium Tetracopper (II) Triarsenate (V),” Acta Crystallogr. Mineral Species from the Tolbachik Volcano, Kamchatka Ser. C. 43, 381Ð383 (1987). Peninsula, Russia,” Canad. Miner. 29, (4), 1115Ð1119 (2001). 10. D. S. Rybin, S. K. Filatov, and L. P. Vergasova, “High- 5. S. V. Krivovichev, A. V. Molchanov, and S. K. Filatov, Temperature X-Ray Diffraction of Urusovite, Cu(AsAlO5),” in Proceedings of International Conference on Crystal “Crystal Structure of Urusovite Cu[AlAsO5]: A New Type of a Tetrahedral Aluminoarsenate Polyanion,” Crystallogr. Chemistry and X-Ray Diffraction of Minerals (Inst. Mineral., Reports 45, 793Ð797 (2000). Ural Division, Russian Acad. Sci., Miass, 2007), pp. 228Ð 6. S. V. Krivovichev, S. K. Filatov, and P. K. Burns, “Jahn– 231. Teller Distortion of Copper Polyhedron in Structural Type of 11. L. P. Vergasova, S. K. Filatov, and V. V. Dunin-Bark- Allyuaudite: Crystal Structure of Bradaczekite, ovskaya, “Posteruptive Activity of the First Cone of GFTE NaCu4(AsO4)3,” Zap. Vseross. Mineral. O-va 130 (5), 1Ð8 and Recent Volcanogenic Formation of Bauxites,” Vulkanol. (2001). Seismol., No. 2, 55Ð77 (2007). 7. The Great Fissure Tolbachik Eruption. Kamchatka 1975Ð 1976, Ed. by S. A. Fedotov (Nauka, Moscow, 1984) [in Rus- 12. L. P. Vergasova, S. K. Filatov, M. G. Gorskaya, A. A. Mol- sian]. chanov, S. V. Krivovichev, and V. V. Ananiev, “Urusovite, 8. K.-H. Lii and P.-F. Shin, “Hydrothermal Synthetic Modifi- Cu[AlAsO5], a New Mineral from the Tolbachik Volcano, cations of the Mineral Alluaudite,” Inorg. Chem. 33, Kamchatka, Russia,” Eur. J. Miner. 12 (5/6), 1041Ð1044 3028−3031 (1994). (2002).

GEOLOGY OF ORE DEPOSITS Vol. 51 No. 8 2009