porphyry copper͞hydrothermal deposits II: of ajoite, K ؉ Na)3Cu20Al3Si29O76(OH)16⅐ϳ8H2O) Joseph J. Pluth* and Joseph V. Smith*

Department of Geophysical Sciences, Center for Advanced Radiation Sources (CARS) and Materials Research Science and Engineering Center, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637-1434

Contributed by Joseph V. Smith, July 2, 2002 A crystal from the type locality Ajo, AZ, yielded just enough Many specimens in several museums were examined, and intensity from streaked diffractions using synchrotron x-rays at the finally the present specimen no. 159940 from the National Advanced Photon Source to solve the crystal structure with com- Museum of Natural History of the Smithsonian Institution was ៮ chosen on the basis of uniform slightly greener color and ؍ position (K ؉ Na)3Cu20Al3Si29O76(OH)16⅐ϳ8H2O; triclinic, P1, a fresher appearance’’ than other slightly bluer specimens. After‘‘ ؍ ␤ ,°(1)110.83 ؍ ␣ ,(7)14.522 ؍ c ,(7)13.687 ؍ Å, b (5)13.634 Electron examining many crystals, one was found that gave streaked .%12.5 ؍ refined to a final R ;(1)105.68 ؍ ␥ ,(1)107.21 microprobe analysis yielded a similar chemical composition that is diffractions with intensity just good enough to solve the main slightly different from the combined chemical and electron micro- features of the structure but with a poor agreement factor probe analyses in the literature. The ajoite structure can be de- (ϳ12.5%). The structure has Si͞Al and Na͞K disorder as well scribed as a zeolitic octahedral-tetrahedral framework that com- as poorly defined water molecules, and the agreement factor bines the alternate stacking of edge-sharing octahedral CuO6 reflects the poor crystal quality and is similar to those for layers and curved aluminosilicate layers and strings. Channels large-pore zeolites. It is likely that the other bluer ajoite crystals bounded by elliptical 12-rings and circular 8-rings of tetrahedra have undergone partial dehydration and rehydration that has contain (K and Na) ions and water. The Al atoms occupy some of damaged the regularity of the crystal structure. the Si tetrahedral sites. Each Cu atom has near-planar bonds to four Materials and Methods oxygen atoms plus two longer distances that generate a distorted ϫ ϫ ␮ 3 octahedron. Valence bond estimates indicate that 8 oxygen atoms A crystal of ajoite, 60 15 5 m , was mounted on the tip of ␮ of 46 are hydroxyl. Only one alkali atom was located in distorted a glass fiber tapered to 1 m. Data sets were collected at the octahedral coordination, and electron microprobe analyses indi- GeoSoilEnviro and ChemMat-Consortium for Advanced Radi- cate K and Na as major substituents. The water from chemical ation Sources (CARS) sectors 13 and 15 at the Advanced Photon analysis presumably occurs as disordered molecules of zeolitic type Source (Argonne, IL). The data set used in the refinement was not giving electron density from diffraction. The high R factor collected using radiation from a diamond (111) crystal at a results from structural disorder and many weak intensities close to wavelength of 0.56954 Å and focused using horizontal and detection level. The crystal chemistry is compared with , vertical Rh-coated float glass Kirkpatrick–Baez mirrors to pro- duce a 100 ϫ 100-␮m2 beam. Data were collected using a Bruker Cu5(SiO3)4(OH)2, and planche´ite, Cu8Si8O22(OH)4⅐H2O, both found in oxidized deposits of Arizona but only the former directly 6000 SMART charge-coupled device detector at a fixed angle of 28° 2⌰ and frame widths in ␸ of 0.3° with a 2-sec counting time with ajoite. per frame. The charge-coupled device detector was mounted on a Huber 4-circle diffractometer with the ␻ axis of the diffrac- microcrystal ͉ microporous ͉ copper silicates tometer in the plane of the ring. Two full rotations of the ␾ axis yielded 1,200 frames with ␹ ϭ 0° and 1,200 with ␹ ϭ 270°. The ៮ ydrothermal deposits supply most of the copper plus symmetry is triclinic: P1. Unit-cell dimensions, a ϭ Hsignificant molybdenum, gold, and other metals important 13.634(5) Å, b ϭ 13.687(7) Å, c ϭ 14.522(7) Å, ␣ ϭ 110.833(11)°, for human welfare. Great advances in understanding the differ- ␤ ϭ 107.208(13)°, ␥ ϭ 105.680(10)°, were refined by least squares ent types of hydrothermal ore deposits have occurred over the using 863 reflections. Data were integrated and corrected for past three decades (1). In general, various granitic bodies intrude Lorentz, polarization, and background effects using Bruker the crust in continental margins and interiors that are composed software (SAINTPLUS). Systematic errors such as beam decay and of volcanic rocks and sediments. Hot brines of many chemical absorption were corrected with the program SADABS on the basis types (2) permeate the existing rocks to generate diverse of the intensities of equivalent reflections. A total of 44,861 assemblages (3). This series of papers concentrates on the reflections was obtained from 3 to 58° 2␪; of the 18,567 unique ϭ porphyry copper deposits of Arizona. Paper I described the reflections (RINT 3.0%), 12,110 were classed as observed ͉ ͉ Ͼ ␴ crystal structures of chenevixite and luethite, two copper Fe͞Al ( Fo 4 F). The crystal structure was refined using SHELXTL 6.12, arsenate (4). This paper covers ajoite, a rare, F2, and isotropic temperature factors to a final R of 12.5%. When beautiful, blue-green mineral (5) that has challenged crystallog- scaled to Cu, the largest peak on the final difference Fourier was raphers for four decades. Structural relations in copper oxysalt ϳ3 electrons per Å3. Final atomic coordinates are shown in minerals are reviewed in ref. 6, and static and Jahn–Teller Table 1, and selected bond distances are shown in Table 2. chemical-bonding effects in Cu(II) oxysalts are reviewed in ref. 7. Electron microprobe analysis was done on four crystals with Ajoite occurs rarely in the oxidized zone of porphyry copper 5–8 analyses completed on a polished surface of crystalline deposits in Arizona (3). Type crystals are blue-green laths or fragments mounted in epoxy using standard wavelength- plates originally listed as monoclinic but now are known to be dispersive techniques and standards: K, asbestos microcline; Na, triclinic from x-ray diffraction study (8). The first sample for amelia albite; Si and Al, anorthite; and Cu, metal. The Si, Al, and chemical analysis (5) was believed to be contaminated with , and a new combined chemical and electron microprobe *To whom reprint requests may be addressed. E-mail: [email protected] or analysis (8) is given in reference books. [email protected].

11002–11005 ͉ PNAS ͉ August 20, 2002 ͉ vol. 99 ͉ no. 17 www.pnas.org͞cgi͞doi͞10.1073͞pnas.132391299 Downloaded by guest on September 29, 2021 Table 1. Atomic coordinates (؋104) and isotropic displacement Cu analyses were equal within experimental error, but the parameters, U,(Å2 ؋ 103) for ajoite average Na and K analyses for each crystal varied. Atoms per 20 xyzUCu atoms: K 0.20, 1.29, 0.23, and 2.15; Na 0.15, 0.65, 0.10, and 1.57; (Na ϩ K) add up to 0.35, 1.94, 0.33, and 3.72 atoms per unit. Cu(1) 905 (1) 2149 (1) 4795 (1) 6 (1) Because of ajoite instability in the electron beam (8), we decided Cu(2) 2917 (1) 1663 (1) 4821 (1) 6 (1) to prefer the conventional bulk analyses for alkalis and not to Cu(3) Ϫ3123 (1) 3137 (1) 4739 (1) 7 (1) Cu(4) Ϫ1117 (1) 2633 (1) 4739 (1) 7 (1) make electron probe analyses of the crystal used for x-ray Cu(5) 6937 (1) 674 (1) 4870 (1) 7 (1) diffraction. Cu(6) Ϫ5122 (1) 3618 (1) 4779 (1) 8 (1) Bearing in mind the evidence for half the bulk water being Cu(7) 4904 (1) 1143 (1) 4814 (1) 5 (1) zeolitic, the formula in ref. 8 was amended to give (K ϩ Cu(8) 8985 (1) 236 (1) 4971 (1) 6 (1) Na)ϳ Cu Al Si O (OH) ⅐ϳ8H O for bulk analysis. This as- Cu(9) 948 (1) 4663 (1) 4917 (1) 8 (1) 3 20 3 29 76 16 2 Cu(10) 2895 (1) 4106 (1) 4811 (1) 8 (1) sumes that one cation, K, fills the atomic site obtained from x-ray Si(1) 6643 (1) 3950 (1) 7006 (1) 5 (1) diffraction, and the remaining K and Na are located in the cavity Si(2) 701 (1) 3064 (1) 7035 (1) 5 (1) associated with water molecules. No doubt the alkali and water Si(3) 4619 (1) 4426 (1) 7031 (1) 7 (1) contents of ajoite vary from spot to spot depending on the salt Si(4) 2748 (1) 2604 (1) 7058 (1) 5 (1) content of hydrothermal brines during original growth and the Si(5) Ϫ713 (1) 4667 (1) 2873 (1) 6 (1) humidity after collection. Possibly ion exchange has occurred Si(6) 1296 (1) 4192 (1) 2741 (1) 8 (1) ϩ ϩ ϩ Si(7) 6719 (1) 1773 (1) 7118 (1) 5 (1) between K ,Na , and H . Si(8) 7100 (1) Ϫ524 (1) 2641 (1) 7 (1) Si(9) 5006 (1) Ϫ103 (1) 2554 (1) 6 (1) Results and Discussion Si(10) 8838 (1) 1424 (1) 7223 (1) 6 (1) The ajoite structure consists of alternating CuO octahedral Si(11) Ϫ2735 (1) 2659 (1) 2552 (1) 7 (1) 6 Si(12) Ϫ2213 (1) 602 (1) 1340 (1) 10 (1) sheets and SiO4 tetrahedral layers composed of chains and Si(13) 8941 (1) 292 (1) 8708 (1) 9 (1) strings. Note that sites labeled Si may contain some Al. Fig. 1 is Si(14) 3420 (1) 763 (1) 1332 (1) 11 (1) a projection down the a axis showing oxygen and hydroxyl atoms Si(15) 95 (1) 1594 (1) 1263 (1) 10 (1) at the vertices of octahedra and tetrahedra. A sheet of edge- Ϫ Si(16) 4746 (1) 3171 (1) 2625 (1) 7 (1) c ϳ O(1) 64 (3) 2350 (3) 5707 6 (1) shared octahedrally coordinated Cu atoms lies at 0.5 (Fig. O(2) 2093 (3) 1867 (3) 5737 (3) 6 (1) 1). Above and below the Cu layer are bands of Si tetrahedra O(3) 6127 (3) 964 (3) 5795 (3) 8 (1) (centered at c ϳ 0.0 and c ϳ 1.0). Each band contains four O(4) 7754 (3) 377 (3) 3951 (3) 9 (1) subunits. Each subunit sharing vertices with the Cu sheet consists O(5) 3784 (4) 1511 (4) 3979 (3) 12 (1) of nonlinear chains of edge-sharing 6-rings. These chains are O(6) 5675 (3) 819 (3) 3852 (3) 9 (1) O(7) 4062 (4) 1326 (3) 5717 (3) 10 (1) traced in Fig. 2, a projection down c, with double arrows. The O(8) 1812 (4) 2064 (3) 3988 (3) 11 (1) second subunit is a string of four Si tetrahedra denoted as Si12, O(9) Ϫ2284 (4) 2968 (4) 3830 (4) 14 (1) Si15, Si13, and Si14 (Fig. 2, single arrows). When the two O(10) 9850 (4) 41 (4) 4113 (4) 14 (1) subunits are connected, the tetrahedral layer is based topolog- GEOLOGY O(11) Ϫ152 (4) 2624 (3) 4004 (3) 11 (1) ically on a nonplanar twisted two-dimensional net with Si atoms O(12) 8203 (3) 566 (3) 5921 (3) 8 (1) O(13) Ϫ4252 (4) 3529 (3) 3914 (3) 11 (1) in rings of 5, 6, and 7 (Fig. 2) with the 5-, 7-, and elliptical 6-rings O(14) 2084 (4) 4287 (3) 5734 (3) 11 (1) resulting from the linkage between chains and strings. A center O(15) Ϫ92 (3) 5202 (3) 4187 (3) 8 (1) of symmetry generates two identical subunits and a double string O(16) 6069 (3) 3324 (3) 5678 (3) 8 (1) of four Si tetrahedra. Fig. 3, a projection down b, shows in more O(17) 4066 (3) 3796 (3) 5711 (3) 7 (1) detail the stacking of the four layers. Each gap between strings O(18) 7972 (4) 2725 (3) 5554 (3) 11 (1) O(19) 1816 (4) 4601 (3) 4041 (3) 11 (1) is occupied by K. The three-dimensional octahedral-tetrahedral O(20) 5889 (4) 4500 (3) 7500 (3) 13 (1) net contains a two-dimensional channel system defined by O(21) 2109 (4) 5035 (4) 2467 (4) 16 (1) elliptical 12-rings along a (Fig. 1) and circular 8-rings along b O(22) 9944 (4) 2541 (4) 7561 (4) 15 (1) (Fig. 3). As is typical of Cu(II)–O linkages, each Cu atom has O(23) Ϫ1907 (4) 3607 (4) 2371 (4) 16 (1) four short distances to adjacent oxygen atoms in a square and O(24) 7999 (4) 1910 (4) 7636 (3) 15 (1) O(25) 6778 (4) 3047 (4) 7452 (4) 15 (1) two longer distances to generate opposing vertices of a distorted O(26) 2969 (4) 272 (4) Ϫ6 (4) 20 (1) octahedron. The short distances generate strings of edge-shared O(27) Ϫ935 (4) 5595 (4) 2513 (4) 16 (1) squares. O(28) 9270 (4) 820 (4) 7927 (4) 18 (1) The chemical analyses indicate that 3 of the 32 tetrahedral sites O(29) 6896 (4) Ϫ1836 (4) 2402 (3) 15 (1) are occupied by Al. From the distances in Table 2, the larger Al O(30) Ϫ2887 (4) 1410 (4) 1764 (4) 17 (1) ϳ ͞ Ϫ atoms should be occupying 1 2 of sites Si(12) 1.67 Å; Si(14) O(31) 4690 (4) 4287 (4) 2449 (4) 16 (1) ͞ O(32) Ϫ3963 (3) 2689 (3) 2113 (3) 12 (1) 1.67 Å and 1 4 of Si(13) 1.63 Å, Si(15) 1.65 Å. This accounts for O(33) 73 (4) 4247 (4) 2335 (4) 16 (1) the three Al atoms per unit cell obtained from the microprobe O(34) 9320 (5) Ϫ756 (5) 8510 (5) 30 (1) analysis. All these tetrahedra reside in the strings of four O(35) 3984 (4) Ϫ1238 (3) 2325 (3) 14 (1) tetrahedra, near the K site and the sites containing 1͞2 Al share O(36) 1120 (4) 2912 (4) 2001 (4) 19 (1) O(37) 4489 (3) 417 (3) 1793 (3) 12 (1) oxygen atoms with K. All other tetrahedra have mean T–O O(38) Ϫ901 (4) 1485 (4) 1699 (4) 19 (1) distances near 1.61–1.62 Å, indicating occupancy with only Si. It O(39) 3887 (4) 3713 (3) 7466 (3) 14 (1) should be noted that bonding to other species may perturb mean O(40) 7808 (4) Ϫ187 (4) 2002 (4) 16 (1) T–O distances in frameworks up to 0.02 Å, and a linear plot from O(41) 5847 (3) Ϫ557 (3) 2126 (3) 12 (1) Si–O ϳ 1.61 to Al–O ϳ 1.74 Å cannot be strictly used to predict O(42) 9606 (4) 1315 (4) 9971 (4) 24 (1) O(43) 1918 (4) 3038 (3) 7518 (3) 14 (1) Al substitution in Si positions. Whether ordered domains or a O(44) Ϫ6046 (4) 2217 (4) 1934 (4) 17 (1) superstructure occurs rather than random disorder is not clear O(45) 7562 (4) Ϫ253 (4) 8291 (4) 19 (1) from the present x-ray data. A thorough transmission electron O(46) Ϫ6211 (4) 4054 (4) 3988 (4) 14 (1) diffraction study of ajoite is desirable. K 4955 (4) Ϫ269 (3) 1 (4) 38 (1) Ajoite contains three types of oxygen atoms: those bonded to W(1) 2462 (16) 2448 (15) Ϫ39 (15) 73 (7) ͞ W(2) 1059 (12) 3156 (13) Ϫ31 (12) 61 (5) Si plus 3 Cu, those bonded to 2 Si Al, and those bonded to 3 Cu. The valence sum for tetrahedral Si plus 3 octahedral divalent Cu,

Pluth and Smith PNAS ͉ August 20, 2002 ͉ vol. 99 ͉ no. 17 ͉ 11003 Downloaded by guest on September 29, 2021 Table 2. Bond lengths (Å) for ajoite

Cu octahedra Cu(1)–O(8) 1.938 (5) Cu(6)–O(46) 1.959 (4) Cu(1)–O(11) 1.969 (4) Cu(6)–O(13) 1.964 (4) Cu(1)–O(1) 1.988 (3) Cu(6)–O(17) 1.979 (4) Cu(1)–O(2) 2.012 (4) Cu(6)–O(16) 1.994 (4) Cu(1)–O(10) 2.501 (5) Cu(6)–O(5) 2.482 (4) Cu(1)–O(14) 2.516 (4) Cu(6)–O(46) 2.747 (5) Cu(2)–O(5) 1.935 (5) Cu(7)–O(5) 1.952 (4) Cu(2)–O(8) 1.968 (4) Cu(7)–O(7) 1.977 (4) Cu(2)–O(2) 1.975 (4) Cu(7)–O(3) 1.984 (4) Fig. 1. Ajoite structure projected down a showing the CuO6 layer, SiO4 Cu(2)–O(7) 1.989 (4) Cu(7)–O(6) 1.984 (4) bands, and 12-ring channels. K atoms are shown as black circles. Cu(2)–O(17) 2.509 (4) Cu(7)–O(3) 2.517 (4) Cu(2)–O(12) 2.640 (4) Cu(7)–O(16) 2.569 (4) Cu(3)–O(18) 1.959 (4) Cu(8)–O(10) 1.954 (5) and for 2 T, is ϳ2, whereas for 3 Cu is ϳ1. This means that to Cu(3)–O(13) 1.975 (4) Cu(8)–O(10) 1.967 (5) achieve charge balance, the O atoms bonded to 3 Cu must really Cu(3)–O(9) 1.981 (5) Cu(8)–O(12) 1.983 (4) be OH groups. There are 16 of these oxygen atoms, so the Cu(3)–O(16) 1.983 (4) Cu(8)–O(4) 1.989 (4) chemical formula is written with (OH) . Cu(3)–O(19) 2.673 (4) Cu(8)–O(2) 2.493 (4) 16 A position on a center of symmetry in ajoite was split into two Cu(3)–O(6) 2.728 (4) Cu(8)–O(1) 2.500 (4) Cu(4)–O(11) 1.924 (4) Cu(9)–O(14) 1.962 (4) positions with half occupancy to explain the elongated electron Cu(4)–O(18) 1.952 (4) Cu(9)–O(19) 1.973 (4) distribution. The distances to adjacent oxygen atoms are large Cu(4)–O(9) 2.015 (4) Cu(9)–O(15) 1.978 (4) enough for most of the site to be occupied by K rather than Na. Cu(4)–O(1) 2.026 (3) Cu(9)–O(15) 1.983 (4) No clear positions for Na and water were obtained from the Cu(4)–O(15) 2.546 (4) Cu(9)–O(11) 2.392 (4) diffractions, indicating structural disorder. Fig. 3 shows a K Cu(4)–O(4) 2.663 (4) Cu(9)–O(9) 2.792 (5) position in distorted octahedral coordination, which accounts for Cu(5)–O(3) 1.979 (4) Cu(10)–O(46) 1.942 (5) only one of the cations. The distances in Table 2 range from 2.73 Cu(5)–O(4) 1.981 (4) Cu(10)–O(14) 1.966 (4) to 2.99 Å. Additional (K and Na) and water from the chemical Cu(5)–O(12) 2.017 (4) Cu(10)–O(17) 1.991 (4) analysis presumably reside in the channels, as disordered mol- Cu(5)–O(6) 2.019 (4) Cu(10)–O(19) 1.994 (4) ecules do in zeolites, and are not detected. Note that atoms listed Cu(5)–O(7) 2.390 (4) Cu(10)–O(8) 2.402 (4) as W in Table 1 are possible sites for water molecules or Naϩ. For Cu(5)–O(18) 2.430 (4) Cu(10)–O(13) 2.793 (4) zeolitic materials, the details of ionic bonding are complex. Si tetrahedra Of the other minerals in the Arizona porphyry deposits, Si(1)–O(25) 1.614 (4) Si(5)–O(33) 1.612 (5) shattuckite and planche´ite (9) come closest in chemical bonding. Si(1)–O(21) 1.614 (5) Si(5)–O(15) 1.616 (4) The crystal structure of shattuckite has octahedral Cu–O layers, Si(1)–O(20) 1.615 (4) Si(6)–O(36) 1.600 (5) but the cross-linkage is by pyroxene-type silicate chains. There Si(1)–O(16) 1.622 (4) Si(6)–O(21) 1.617 (5) are no zeolitic water molecules and no alkali or aluminum Si(2)–O(27) 1.614 (5) Si(6)–O(19) 1.619 (4) Si(2)–O(43) 1.614 (5) Si(6)–O(33) 1.629 (5) cations. In planche´ite, the octahedral sheets are cross-linked by Si(2)–O(22) 1.619 (5) Si(7)–O(25) 1.606 (5) amphibole-type silicate chains, and a small amount of water is Si(2)–O(1) 1.624 (2) Si(7)–O(24) 1.611 (5) indicated. The linkage of short Cu–O distances in both structures Si(3)–O(31) 1.613 (5) Si(7)–O(35) 1.615 (4) also generates an edge-shared string. Si(3)–O(17) 1.613 (4) Si(7)–O(3) 1.630 (4) Si(3)–O(20) 1.622 (5) Si(8)–O(40) 1.612 (5) Conclusions Si(3)–O(39) 1.624 (4) Si(8)–O(29) 1.628 (4) The crystal structure of ajoite opens up a further window into Si(4)–O(29) 1.610 (4) Si(8)–O(41) 1.631 (4) zeolitic (microporous) materials. Ion-exchange experiments are Si(4)–O(39) 1.615 (4) Si(8)–O(4) 1.634 (4) needed to determine the selectivities and possible industrial use. Si(4)–O(43) 1.616 (5) Si(9)–O(37) 1.611 (4) Removal of the zeolitic water molecules may permit molecular Si(4)–O(2) 1.618 (4) Si(9)–O(41) 1.619 (4) sorption or catalysis. A theoretical study of polygonal linkages Si(5)–O(23) 1.598 (5) Si(9)–O(6) 1.627 (4) may allow invention of new octahedral-tetrahedral frameworks, Si(5)–O(27) 1.601 (4) Si(9)–O(35) 1.628 (4) Si(10)–O(28) 1.607 (5) Si(13)–O(45) 1.645 (5) Si(10)–O(12) 1.615 (4) Si(13)–O(28) 1.650 (5) Si(10)–O(22) 1.623 (5) Si(14)–O(26) 1.657 (5) Si(10)–O(24) 1.626 (5) Si(14)–O(45) 1.667 (5) Si(11)–O(30) 1.597 (5) Si(14)–O(37) 1.679 (4) Si(11)–O(9) 1.622 (5) Si(14)–O(44) 1.690 (5) Si(11)–O(32) 1.623 (4) Si(15)–O(34) 1.634 (6) Si(11)–O(23) 1.629 (5) Si(15)–O(42) 1.650 (5) Si(12)–O(26) 1.658 (5) Si(15)–O(38) 1.652 (5) Si(12)–O(38) 1.663 (5) Si(15)–O(36) 1.653 (5) Si(12)–O(40) 1.681 (5) Si(16)–O(44) 1.619 (5) Si(12)–O(30) 1.687 (5) Si(16)–O(13) 1.619 (4) Si(13)–O(34) 1.613 (6) Si(16)–O(31) 1.622 (5) Si(13)–O(42) 1.628 (5) Si(16)–O(32) 1.622 (4) K octahedra K–O(30) 2.731 (7) K–O(30)#6 2.863 (6) K–O(37) 2.761 (6) K–O(37)#8 2.878 (6) Fig. 2. SiO4 tetrahedral layer looking down c. The block double arrows trace K–O(26) 2.829 (7) K–O(26) 2.993 (6) nonlinear chains of 6-rings, block single arrows denote four-SiO4 strings, and 5, 6, and 7 give the number of tetrahedron in rings.

11004 ͉ www.pnas.org͞cgi͞doi͞10.1073͞pnas.132391299 Pluth and Smith Downloaded by guest on September 29, 2021 and a family of copper silicate zeolitic materials may ensue. Finally, we emphasize the importance of synchrotron x-ray facilities for the x-ray structure determination and the need for complex spectroscopic techniques to help resolve the many details left undetermined. Ajoite has not been reported yet in corroded copper art objects but might be found along with planche´ite.

We thank Peter Burns for parallel study and manuscript review, the curators of the Smithsonian National Museum of Natural History facility for specimens, and Ian M. Steele for the electron probe analysis. J.J.P. thanks the Materials Research Science and Engineering Center at the University of Chicago for support. This work was performed at the GeoSoilEnviroCARS (GSE-CARS) Sector 13, and ChemMat-CARS Sector 15 of the Advanced Photon Source at Argonne National Labo- ratory. GSE-CARS and ChemMat-CARS are supported by the National Science Foundation, Department of Energy, and W. M. Keck Founda- tion. Use of the Advanced Photon Source was supported by the U.S.

Fig. 3. Ajoite structure projected down b showing the positions of CuO6 Department of Energy, Basic Energy Sciences, Office of Energy Re- layers, SiO4 6-ring chains, four-SiO4 strings, K sites, and 8-ring channels. search, under Contract W-31-109-Eng-38.

1. Guilbert, J. M. (2001) Mining Eng., October, 29–35. 5. Schaller, W. T. & Vlisidis, A. C. (1958) Am. Mineral. 43, 1107–1111. 2. Cloos, M. (2001) Int. Geol. Rev. 43, 285–311. 6. Eby, R. K. & Hawthorne, F. C. (1993) Acta Crystallogr. B 49, 28–56. 3. Anthony, J. W., Williams, S. A., Bideaux, R. A. & Grant, R. W. (1995) 7. Burns, P. C. & Hawthorne, F. C. (1996) Can. Mineralogist 34, 1089–1105. Mineralogy of Arizona (Univ. of Arizona Press, Tucson), 3rd Ed. 8. Chao, G. Y. (1981) Am. Mineral. 66, 201–203. 4. Burns, P. C., Smith, J. V. & Steele, I. M. (2000) Mineral. Mag. 64, 25–30. 9. Evans, H. T., Jr., & Mrose, M. (1977) Am. Mineral. 62, 491–502. GEOLOGY

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