Topic
Plancheite
About: Plancheite is a research topic. Over the lifetime, 13 publications have been published within this topic receiving 153 citations. The topic is also known as: planchéite.
Papers
TL;DR: In this article, a series of natural and synthetic copper(II) silicate minerals can be readily obtained, have paramagnetic shifts far outside known chemical shift ranges, and potentially are very sensitive to structural details involving interactions of paramagnetic cations and Si sites.
Abstract: Abstract 29Si NMR has only rarely been applied to silicate minerals in which the predominant cations have unpaired electron spins (e.g., most transition metals and REE), because of the potential for serious line broadening and signal loss. However, as shown here, spectra for a series of natural and synthetic copper(II) silicate minerals can be readily obtained, have paramagnetic shifts far outside known chemical shift ranges, and potentially are very sensitive to structural details involving interactions of paramagnetic cations and Si sites. Signals from different silicon sites in the structures can be distinguished and quantified. Peak broadening due to magnetic couplings and to disorder can be large, but not to the point of “non-observability.” NMR signal loss can be related to specific, and in some cases improvable, technical issues such as excitation bandwidth, sample spinning speed, and rapid nuclear spin relaxation. Two samples of the “mineraloid” chrysocolla from different copper ore deposits have very similar spectra with significant paramagnetic shifts, suggesting strong Si-Cu interactions and a common stoichiometry and short-range structure.
11 citations
1 Jan 1999
TL;DR: Shlomovitch et al. as discussed by the authors showed that copper mineralization in the Timna Formation occurs in the dolomitic, sandy, and shaly lithofacies of the Upper Sasgon Member.
Abstract: Shlomovitch, N., Bar-Matthews, M., Segev, A., Matthews, A. 1999. Sedimentary and epigenetic copper mineral assemblages in the Cambrian Timna Formation, southern Israel. Isr. J. Earth Sci. 48: 195‐208. Copper mineralization in the Timna Formation occurs in the dolomitic, sandy, and shaly lithofacies of the Upper Sasgon Member. Scanning electron microscope, chemical, and isotopic studies of the copper mineral parageneses indicate an evolution from diagenetic, neutral reducing conditions through stages of epigenetic alteration at oxidizing and progressively more acid conditions. Primary copper sulfide minerals are djurleite (Cu 1.93 S) and covellite (CuS) with minor chalcocite (Cu 2–1.93 S), digenite (Cu 1.8 S), and anilite (Cu 1.75 S) randomly dispersed in the dolomitic lithofacies. δ 34 S values of –14‰ are consistent with their formation by reduction of marine sulfate. Subsequent evolution of the ores involves their replacement by malachite (Cu 2 (OH) 2 CO 3 ), which armors and replaces the sulfide minerals, followed by the development of paratacamite (Cu 2 (OH) 3 Cl) as veins emanating from the altered sulfides. The malachite alteration stage represents a change to oxidizing conditions; paratacamite develops with a decrease in pH and in the presence of chloride ion, which allows the development of stable aqueous copper chloride complexes. The first copper mineral to form in the sandy and shaly lithofacies is chrysocolla (Cu 2–X SiO 5 (OH) 3 ·yH 2 O), which forms by the dissolution of precursor silicate minerals (quartz, clays, feldspars). The chrysocolla subsequently evolves into plancheite (Cu 8 (Si 4 O 11 ) 2 (OH) 4 ·yH 2 O), pseudomalachite (Cu 5 (OH) 4 PO 4 ), and dioptase (CuSiO 3 ·H 2 O). Thermodynamic calculation indicates that copper silicate formation was brought about by a decrease in pH and/or increase in aCu and is thus consistent with the evidence for epigenesis in the dolomitic lithofacies.
11 citations
TL;DR: The X-ray diffraction pattern of chrysocolla is rather poor; however diffraction patterns were obtained after controlled heating (DTA), these indicated the crystallization of tenorite, cuprite, quartz and cristobalite as mentioned in this paper.
Abstract: Timna' chrysocolla was divided into several types based on two end members differing in water content, specific gravity, CuO:SiO2 ratio and apparently also in their DTA behaviour. The chrysocolla replaces quartz. In places an intergrowth of chrysocolla and wilkeite was observed by electron probe scanning. The X-ray diffraction pattern of chrysocolla is rather poor; however diffraction patterns were obtained after controlled heating (DTA). These indicated the crystallization of tenorite, cuprite, quartz and cristobalite. Dioptase, plancheite and bisbeeite were also identified by X-ray diffraction. Several possibilities of chrysocolla genesis are discussed.
10 citations
TL;DR: Raman (and infrared) spectroscopy proves that water is in the molecular structure of shattuckite; thus the formula is better written as Cu(5)(SiO(3))(4)(OH)(2)·xH(2)O.
10 citations
TL;DR: 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⋅∼8H2O, which can be described as a zeolitic octahedral-tetrahedral framework.
Abstract: 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 plancheite, Cu8Si8O22(OH)4.H2O, both found in oxidized copper deposits of Arizona but only the former directly with ajoite.
9 citations
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Performance Metrics
| Year | Papers |
|---|---|
| 2017 | 1 |
| 2014 | 1 |
| 2013 | 1 |
| 2012 | 4 |
| 2002 | 1 |
| 1999 | 1 |