Pluth Joseph J, Smith Joseph V
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, USA.
Proc Natl Acad Sci U S A. 2002 Aug 20;99(17):11002-5. doi: 10.1073/pnas.132391299. Epub 2002 Aug 13.
A crystal from the type locality Ajo, AZ, yielded just enough intensity from streaked diffractions using synchrotron x-rays at the Advanced Photon Source to solve the crystal structure with composition (K + Na)3Cu20Al3Si29O76(OH)16* approximately 8H2O; triclinic, P1, a = 13.634(5) A, b = 13.687(7), c = 14.522(7), alpha = 110.83(1) degrees, beta = 107.21(1), gamma = 105.68(1); refined to a final R = 12.5%. Electron microprobe analysis yielded a similar chemical composition that is slightly different from the combined chemical and electron microprobe analyses in the literature. The ajoite structure can be described as a zeolitic octahedral-tetrahedral framework that combines the alternate stacking of edge-sharing octahedral CuO6 layers and curved aluminosilicate layers and strings. Channels bounded by elliptical 12-rings and circular 8-rings of tetrahedra contain (K and Na) ions and water. The Al atoms occupy some of the Si tetrahedral sites. Each Cu atom has near-planar bonds to four oxygen atoms plus two longer distances that generate a distorted octahedron. Valence bond estimates indicate that 8 oxygen atoms of 46 are hydroxyl. Only one alkali atom was located in distorted octahedral coordination, and electron microprobe analyses indicate K and Na as major substituents. The water from chemical analysis presumably occurs as disordered molecules of zeolitic type not giving electron density from diffraction. The high R factor results from structural disorder and many weak intensities close to detection level. The crystal chemistry is compared with shattuckite, Cu5(SiO3)4(OH)2, and planchéite, Cu8Si8O22(OH)4.H2O, both found in oxidized copper deposits of Arizona but only the former directly with ajoite.
来自亚利桑那州阿霍矿产地的一块晶体，利用先进光子源的同步加速器X射线，从条纹衍射中获得了足够的强度，从而解析出其晶体结构，其成分为(K + Na)3Cu20Al3Si29O76(OH)16·约8H2O；三斜晶系，P1，a = 13.634(5) Å，b = 13.687(7)，c = 14.522(7)，α = 110.83(1)°，β = 107.21(1)，γ = 105.68(1)；最终精修R值为12.5%。电子微探针分析得出的化学成分与之相似，但与文献中化学分析和电子微探针分析相结合的结果略有不同。硅孔雀石结构可描述为一种沸石型八面体 - 四面体骨架，它结合了边共享八面体CuO6层与弯曲的铝硅酸盐层及链的交替堆叠。由四面体的椭圆形12元环和圆形8元环界定的通道中含有(K和Na)离子及水。铝原子占据了一些硅四面体位置。每个铜原子与四个氧原子形成近平面键，另外还有两个较长的距离，形成一个扭曲的八面体。价键估算表明，46个氧原子中有8个是羟基。仅一个碱金属原子位于扭曲的八面体配位中，电子微探针分析表明K和Na是主要取代基。化学分析中的水可能以沸石型无序分子形式存在，在衍射中未给出电子密度。较高的R值是由结构无序以及许多接近检测水平的弱强度造成的。将该晶体化学与同样发现于亚利桑那州氧化铜矿床中的硅铜矿Cu5(SiO3)4(OH)2和水硅铜矿Cu8Si8O22(OH)4·H2O进行了比较，不过仅将前者与硅孔雀石直接进行了比较。
