CanadianMineralogist, Vol. lZ pp.207-210(1973)

OPTICAI ABSORPTIONSPECTRA OF Cu2+ lN CHALCAhITHITEAND MAIACHITE

S.V. I. IAKSHMAN eno B. l. REDDY Depo,rtrnentof Phgsias,Sri VmkateswaraUnioersitg, Tirupati" Indin

ABsrBAsr E:malachite have been studied at room and liouid air University Geology Museum) and malachite tempsratures.From tle nature of the spectra, and (Chamadala A. P., lrdia) were recordedat room large copper crmtents,the observedbands in both and liquid air temperatures on a medium quartz samplesare attributed to Cu2+ in tetragonal sym- spectrograph in the wavelength region 9500- metry. The crystal parameterswhich give a good fit ?,, to the observedband positions arg for chalcanthite 20004. fu it was not possibleto cut the crystals and malac"hiterespectively : Dq-12.50,-1250; Ds-3240, either parallel or perpendicular to their optic -3245: Dt-710,-700; l-830 -830. a.xes,they were cut at random from the massive mm for chalcantlrite The observedfeatures and band shifts indicate that samples.Crystals 1.5 thick the vibronic interactions are greater in chalcanthite and 2.3 mm thi& for malachite were found than in malachite. suitable for the study of their absorption spectra. Using polarized and unpolarized incident beams of radiation, spectrawere recordedon Kodak IN, ImnopusrroN Ilford R.40 and Zenith plates in 20 to 30 mi. The structure of chalcanthite, triclinic CuSOa : nutes. Wavelengths and oscillator strengths of SFIzO, was determined by Beevers & Lipson the bands were meaflred as detailed in Laksh- (1934). The mineral contains two non-equi- man et al. (1972). valent ionic groups per unit cell. The environ- ment of eadr ion consists of four water molecules THponv ananged in an approximate squa.re with two Divalent copper (Cu'*) has an electronic polar sulphate oriygens at slightly gxeater dis- structure (A)3d9. Lr Oa qfmmetry the ground tances from the Cu2+ central metal ion. The state electron configuration for Cu2+ is wriften field experiencedby the ions has a strongly tetra- (t2)6(e)s which gives rise to a 2E state. When gonal component along the axis joining the sul- one electron from the tz orbit is promoted to the phate ion. to the e orbit the resulting configuration (tz)6 2T Malachite,Cu2(OH)2. COs, is monoclinicand (e)a gives rise to a state. Thus, one single has oxygens of 01 equally displaced at transition (i.e. one single band) is expectedfor ^foru 28, 1.984 and two other oxygens at distances equal Cu2+ in O'' qymmetry. As the ground state, to 2,714 from the central Cu2+ ion (Orgel is often split under the Jahn-Teller effect, we 1960). can not have a regular octahedrally-coordinated Cu2+ complex (Ballhausen 1962). Although the optical obsorption spectrum of chalcanthite has not been reported in t}r'e litera- In a tetragonal (quadrate) field, the ground 2E 'Ar) turg the spectrum of malachite at room tempera- would be split into two levels (281 and zTz ture was studied by Hunt Salisbury (1971). and similarly the upper would be split into & 'zE) They found only one broad band in the visible trto (2Bz and levels. If, in addition, spin region at 80004 and tfuee others in the infra- orbit interaction is taken into consideration, the 'zE red x 2.29p",2.116 and 2.52p,. They ground would be split into two and the upper attributed 2Tz the band in the visible spectrum to a 2E->2Tz into three levels. The resulting energy levels transition of Cu2+ in O'. qymmetry, and the three for Oa, Dqn and D+a' including spin orbit inter- other bands to the COs" radical. The only other action, are given in Table 1. study of a similar mineral is that of Newham & The complete theory of the energy levels of Santoro (1967), who reported that the reflectance Cuz+, including sprn orbit effect, has been given spectrum of dioptasg CuSiOs . HzO, showed one for various crystal symmetries by Liehr (1960). broad band at 13000cm-1. This was assignedto The energy matrices for quadrate fields are pre' the transition 2Br'-> 28. sented in Table 2.

207 208 THE CANADIAN MINERALOCIST

Rssulrs axo ANelysrs All these featuresindicate a distortion in qym- Chalcanthite metry, probably to one of Dap symmetry. The energy level diagram for Cu2+ is shown both Chalcanthite absorption spectra consist of four for Oa and Dqn fields in Figure 2. The ordering bands, of rnhich two (at 12000 20166 and cm-1) of energy levels is according to Holmes & Mc- are very prominent. The microphotometric pro- Chue (1957). files for these (90'K) are shown in Figure l. The position of the band at 12000cm-1 is an The 12000 cm-1 band is the stronger of the indication of near-octahedral symmetry in the pair; the other two bands weak occw at 16524 crystal (Oye et aI. L964). The first three bands and 18177cm-1. located at 12000 m.-r, Iffi24 cm-1 and 18177 The waveleng:th and wave number data of the cm-1 have been assignedto 281-->2Bz, 2By--> z6t observedbands at room and liquid air tempera- and 2Br-+ 2E transitions respectively, as has tures are given in Table 3. At liquid air temper- been done by Holmes & McClure (1957) in the ature the intense band at 12000 cm-1 exhibirs case of CuSOa.SFI2O,from the magnitude and a marked clrange in intensity for two mutually their relative positions. perpendicular orientations of the Nicol. The tetragonal field splitting parameters Ds and Dt are calculated as follows : TABLEI. ENERGYSTATE CLASSIFICATIONS -3Ds * SDt: I8I77 - 12000: 6177 Synnetry 0h D", ,,, + soin orbit -4Ds-SDt :16521 +n +u ---- - inleraction -?Dr Al A, t- 22701 lo A2 '.Ds -324.0 \17 = crn-L E A1*81 t6*17 T1 A2*U SDt:6177 * 3Ds 16+16+17 : 6177- 97n: -3552 T^ z 82*U 17+f6+17 , .Dt *: -710 cm-l Using these values of Ds and Dt and the free TABLE2. ENERGvMATRIcES FoR THE cor{FIcUMTIoN d' rN A TETRAoo- ion spin-orbit coupling constant, equal to -830 ML FIELD cm-1, the energy matrices for fo and lz given 12t 18 -E lrs 12 ,.rl -4 -41il-Da+4Dt-E TABLE3. ASSIGMENTSFOR THE CU2+ BANDS IN CHALCANTHITE -l - W^r' 6Dq-zDs-6Dt-E banoPosltlons ,.tsslqnmen6 | w.r.i. the qround "2-,8 state I,, vlanu-snt1;8 v'lt'-aoe&t-t", 0 - -toq*n"*3tt'n 8332.0 12000 ?@ | l[2^ f. 6050.0* 16524 6050.0* 16s24 roo ('t) 6W2Ds-Dt-E ssoo.o* 18177 55oo.o* rcvl ri" l2rr) 4gs7.s zot66 4957.5 2o1aa r^D ('rr) *uomDaratormeasure[Ents

FREE Oh ooa 8600 8000 7500 7000 650052005000 toN Frc. 1. Microphotometric profiles of the absorption Frc. 2. Energy level diagram for Cu2+ in Op and spectrum of Cu2+ in chalcanthite at 90"K. D4 fields. oprIcAL ABsoRprroN spEcrBA or Cu2+ rN cHALcANTHTTE AND tvIALAcHrrE 209 in Table 2 have been diagonalized for various The energy level siheme of Cu2+ in chalcan- values of Dq. The enef,gy values thus obtained thite in D+a symmetry, inclusive of spin-orbit are plotted with respect to the ground f? level interaction, is shown in Figure 4 along with the against Dq values in Figrre 3. A good fit of the observedtransitions and bands positions. experimentally-observedband positions is ob- Since some of the band maxima measurements tained for Dq: - 1250cm-1. (measured on the comparator) are approximate, no attempt has been made to calculate the The band positions are calculated with Dq: -t, energiesof the spin-orbit levels for -1250 c,rn-r, Ds : -32410 Dt: -210 various values of and select one which gave a good fit to the cm-t, f, : -830 sr-1 and are" given along with l, observedtransitions and band positions. the observedband positions (90oK), their oscil- lator strengths and corresponding transitions in Malachite Table 4. The malachite spectrum showedbands similar to those of chalcanthite. The only difference is that the first band on the red is at 12000cm-l n:tttr]

(2Ta) N9FTd t2) n3[2 ri (2r2)

nlt"l Frc. 4. Energy level scheme of Cu2 + in chalcanthite in Den symmetry inclusive Dq (cri'l). ro' of spin-orbit interaction. (The superscripts a, b and c are Frc. 3. Energy (inclwive of spin-orbit) level diagram used by the authors to designate of Cu2+ in chalcanthite in tetragonal symmetry different levels). plotted as a function of the crystal field parameter --JlQ Dq, with Ds=-3240 cm-r, Dt cm-r TABLE5. BAI,IDMAXIMA, CRYSTAL AND TETRAGOML FiELD and =-830 cm-1. The solid circles show the f OF CUz+IN CHALCANTHITEAND MALACHITE. orperimental energies at 300'K PAMMFTERS Chalcanthite Malachite TABLE4, OBSERVEDANDCALCULATED ENERGIES, OSCILLATOR STRENGTHSANDASSIGNMENTS OFTHE BANDS FOR CUZ+ IN CHAL- CANTHITE(pq=-IZSO c1-tr^qe=-rp1O sn-), nt=-7'10cm-l and - atZ-t ^ b 12- t L=-830cm-t ) !-7 \ E)+r7 \^r'2) 12000 1l919 - 4 tan\ '6 \ pt 16524 16482 Transition BandPositlons (cm-r) 0scil lator Stpngths tac tzn \ 18177 18160 f, * ton _' \ ^'2r ,rJW S:ff-[ 3oooK ,oj* t*" ZUIOO 20166 "ur-r""d 1'rr) r/ ('rr) 12000 lle03 6.1 7.s rr uq -1250 -tLau -a2Lq r.o ('t\ 16524 16j24 LLL DS -3240 'ts7z7 ri" l2rr) 1s177 lu Dt -710 -700 ruo ("r2) 20166 19404 0.13 0.26 vr -830 -a?n 210 rHE CANADIAN T4INERALOdS:T

for chalcanthite and 11919cm-1 for malachite. AcrNowr.rocslvlENTs polarized The intensity variation in light is not The authors wish to aeress their thanlminerals and rocks - tr. and 20166 crn-1 for chalcanthite, whereas in Carbonates.Modem Geol. 2' 23-30. malaclr.ite the absorption is concentrated in tbree Lar*ruan, S.Y.J., Rool B.]. & Bnrrvresrrvacr$r,]. bands at 16524 cm-l, 18160 cm-1 and 20166 (1972): Optical absorptionspectrum of iron in cm-r (these observed band positions are the gxnet Phgs. Staan Solidi A (Germany) t2, 5211 s€lme as in the chalcanthite). The first intense 524. band at 12000 cm-1 in chalcanthite exhibits a Luun, .dD. (1960): Reciprocationof electrostatic large change in intensity for incident polarized and electromagneticforces in ligand field theory. PhUs.Chem. 64t 43-51. light no change has been observed for l. whereas Ns$rNHAM,RE. & Savronq RP. (196'f) : Magnetic the weak band at 11919 crn-1 in malachite. and optical properties of dioptase PhAs. Status When the crystals were cooled to liquid air Solidi (Gxmany) 19' K87-90. temperatuxe, a blue shift of about 850 cm-1 Oncrr, L.E (1960): An introductian to Trarxitian was observed for the red band in chalcanthite Metal Chemistry. Metluen, Iondon- but no ocrresponding change was observed for Ovr, ItA. & Gnuw, D.M. (1964): Octahedral ab- malachite. sorption spectraof &e dipositive 3d metal ions in From the obssved features it is concluded that molten aluminum chloride. bwrg. Chem. 3, 836- the vibronic interactions in chalcanthite are 84t. muclr greater than those in malachite. Manuscriptreceioeil Maq IW3, emendeilAwst 1973.