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Chrysocolla (Cu, Al)2H2Si2O5(OH)4·nH2O is a hydrated copper hydroxy silicate and is commonly known as a semi-precious jewel. The mineral has an ill defined structure but is said to be orthorhombic, although this remains unproven. Thus, one of the few methods of studying the molecular structure of chrysocolla is to use vibrational spectroscopy. Chrysocolla may be defined as a colloidal mineral. The question arises as to whether chrysocolla is a colloidal system of spertiniite and amorphous silica. The main question addressed by this study is whether chrysocolla is (1) a mesoscopic assemblage of spertiniite, Cu(OH)2, silica, and water, (2) represents a colloidal gel or (3) is composed of microcrystals with a distinct structure. Considerable variation in the vibrational spectra is observed between chrysocolla samples. The Raman spectrum of chrysocolla is characterised by an intense band at 3624 cm−1 assigned to the OH stretching vibrations. Intense Raman bands found at 674, 931 and 1058 cm−1 are assigned to SiO3 vibrations. The Raman spectrum of spertiniite does not correspond to the spectrum of chrysocolla and it is concluded that the two minerals are not related. The spectra of chrysocolla correspond to a copper silicate colloidal gel.

Plancheite Cu8Si8O22(OH)4·H2O is a hydrated copper hydroxy silicate. Raman spectroscopy complimented with infrared spectroscopy has been used to determine the molecular structure of plancheite. Raman bands at around 1048, 1081 and 1127 are described as the ν1-SiO3 symmetric stretching vibrations; Raman bands at 828, 906 are attributed to the ν3-SiO3 antisymmetric stretching vibrations. The Raman band at 699 cm−1 is assigned to the ν4 bending modes of the SiO3 units. The intense Raman band at 3479 cm−1 is ascribed to the stretching vibration of the OH units. The Raman band at 3250 cm−1 is evidence for water in the structure.

Using reflection extended X-ray absorption fine structure spectroscopy (REFLEXAFS) and X-ray photoelectron spectroscopy (XPS) it has been established that Cu(II) in low concentration in aqueous media can be chemisorbed onto the (0001) surface of muscovite mica. From the XPS studies it is suggested that the Cu species is in a similar bonding environment to the copper in copper hydroxide. A depth profile of the reacted mica surface was also carried out using XPS and this suggests that there had been no diffusion of the Cu into the mica surface. REFLEXAFS studies of the reacted mica surface provided information about shells of O, Al/Si, and Cu surrounding a central Cu absorber. The best-fit bond distances are as follows: O–Cu, 1.98 A; Cu–Cu, 2.64 A; Al/Si–Cu, 3.09 A. This provides direct evidence for Cu being bound to the surface at aluminate or silicate groups and suggests that the Cu species adsorbed onto the surface are similar to the copper species found in copper hydroxide, plancheite, and shattuckite. It is proposed that Cu is chemisorbed at atomic imperfections, such as steps and kinks, on the mica surface.

Copper minerals (chrysocolla ≫ dioptase ≫ plancheite > tenorite) plus barite and quartz occur in a small lens of granulite- grade calcite-dolomite marble near Saldán, Córdoba Province (central Argentina, 31°18′50.7″S, 64°19′50.0″W). The mineralization is hosted in fractures (striking N30°E and dipping 78°W) that were widened by dissolution. Chrysocolla mainly fills fractures. It has variable H2O contents but the Cu:Si ratio is always close to 1: 1. Plancheite forms compact fissure fillings and aggregates of interlocking spherules. Copper is partially replaced by Mg (up to 2.22 wt. % MgO), with small amounts of Na, K, Ca, Al and Fe also present. Dioptase occurs as prismatic crystals dominated by {10 10} and {11 21} that can reach over 2 cm in length, and also as granular fracture fillings. Unit-cell parameters are a 14.5719(6), c 7.7799(3) Å, V 1430.7(1) Å3; refractive indices are ε = 1.707(3), ω = 1.656(3), with an anomalous small 2V. Magnesium (up to 0.15 wt. % MgO) is the only significant substituent. Yellow barite crystals tabular on {001} contain traces of Sr. Quartz occurs rarely, as drusy linings. A few cases of botryoidal, opal-like quartz crusts are known. Tenorite forms dark brown masses and stringers included in marble. Very scarce grains of copper sulfides (anilite altering to spionkopite and covellite along rims and cracks) are found scattered in the marble. Copper is partially replaced by Bi (≤ 0.15 wt. % Bi) and Pb (≤ 0.16 wt. % Pb). Malachite and brochantite are alteration products of sulfides. Fluid inclusion studies indicate that the minerals precipitated from a single-phase fluid initially at a temperature above 300°C that cooled to c. 220°C. Salinity was very low, 0 to 2 wt. % NaCl eq. Isotopic analyses of calcite give δ13C values of 0.4-0.9 ‰ PDB and δ18O values of 17.1-15.1 ‰ VSMOW, coincident with the isotopic signature of the regional marbles. Calculated values of δ18O for water in isotopic equilibrium with calcite fall into with the Metamorphic Water Box. The δ34S values of barite are 3.6-4.6 ‰ CDT. The mineralization possibly precipitated from fluids of meteoric origin that suffered an oxygen isotope shift due to a very low water/rock ratio. The sulfur source could have been sedimentary or igneous sulfides, or a mixture from two different sources (such as heavy seawater-derived sulfur and light sedimentary sulfides), but not exclusively seawater. Copper was probably scavenged from accessory sulfides scattered in barren marble or orthoamphibolite. The heat source remains unknown. Fil: Colombo, Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Lira, Raul. Universidad Nacional de Córdoba. Facultad de Cs.exactas Físicas y Naturales. Museo de Geología y Miner.; Argentina Fil: Ripley, Edward. Indiana University; Estados Unidos Fil: González del Tánago, José. Universidad Complutense de Madrid; España

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.

Genesis and evolution of copper silicates in the ore deposit of Mindouli, Congo The weathering processes which affect the sulfide mineralization of Mindouli (Congo) leads to the individualization of various secondary products : carbonates, silicates and oxides. The silicate pangeneses which were recognized consist of dioptase (CuSiO3.H2O), plancheite (Cu7Si8O22(OH)2) and chrysocolla (Cu7Si8O2O(OH)8.8H2O). These different copper silicates can directly result either from the transformation of parent sulfides like chalcocite (Cu2S), or from recrystallizations after the dissolution of the secondary copper minerals (carbonates and silicates), or from the replacement of lead carbonate (PbCO3). In the majority of the studied cases, the transformation is characterized by conservation of original mineral structures so that the chemical composition of secondary cupriferous minerals reflects partly the parent materials from which they derive., Les altérations météoriques qui affectent la minéralisation sulfurée de Mindouli au Congo conduisent à l'individualisation de nombreux produits secondaires : carbonates, silicates et oxydes. Il est mis en évidence différentes générations de silicates de cuivre : dioptase (CuSiO3.H2O), planchéite (Cu7Si8O22(0H)2) et chrysocolle (Cu7Si8O20(OH)8.8H2O). Ces différents silicates de cuivre résultent soit directement de la transformation des sulfures cuprifères parentaux comme la chalcocite (Cu2S), soit de recristallisations à partir de la dissolution des anciens minéraux cuprifères secondaires (malachite, carbonates et silicates de cuivre), soit enfin de pseudomorphoses du carbonate de plomb (cérusite, PbCO3). Dans la majorité des cas analysés, la transformation s'est faite avec conservation de la structure du minéral originel. Aussi la composition chimique des phases secondaires cuprifères reflète-t-elle, en partie, celle du matériau parental., Koud Jean-Mathias. Genèse et évolution des silicates de cuivre dans le gisement de Mindouli au Congo. / Genesis and evolution of copper silicates in the ore deposit of Mindouli, Congo. In: Sciences Géologiques. Bulletin, tome 41, n°3-4, 1988. pp. 279-288.

The orthorhombic crystal structures of shattuckite, Cu(5)( SiO(3))(4)(OH)(2) and planchétite, Cu(8)(Si(4)0(11))(2)(OH)(4) H(2)O, have been solved. Shattuckite contains silicate chains similar to pyroxene in a complex association with copper atoms, while the closely related planchéite contains silicate chains similar to amphibole.