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High-pressure synchrotron X-ray diffraction and infrared absorption spectroscopy have been employed to study the crystal chemistry and phase transitions in an [OH]-bearing carbonate, malachite Cu2(CO3)(OH)2, to determine the effect of [OH] on the stability of carbonate. We found that the crystal structure of malachite is stabilized by a high degree of [CuO6]-octahedron distortion, as is manifested by large variations in Cu–O bond lengths resulting from oxygen atoms that connect to hydrogen at crystallographically different sites. External pressure offsets the effect of hydrogen bond, promotes [CuO6] compression and regularization and accordingly [CO3] rotation. Rotation of [CO3]-triangles, in turn, assists in a conversion in the crystal orientation of the [CuO6] structural unit. During compression to above ~6 ​GPa, malachite begins to turn into the rosasite lattice, accompanied with a jump in density of 3.3%. Rosasite is characterized with a hardened lattice and preserves to the maximum pressure (18.2 ​GPa) of the present study. Phase transformation mechanism of malachite to rosasite is different from that of carbonates, with the latter being driven by an almost uniform compression of [MO6]-octahedron (M ​= ​Ca, Cd, Mn, Fe, Zn, Mg, etc.) and rotation/translation of [CO3]-triangle under pressure.

Divalent metal hydroxycarbonates with M2CO3(OH)2 stoichiometry are widely used in industry and are abundant in nature as the malachite/rosasite group of minerals. Essential to their performance as catalytic precursors and in nanoelectronics, these materials and minerals exhibit a high degree of cation ordering in mixed metal systems due to differences in distortion of the octahedral metal sites. Density-functional theory (DFT) calculations on pokrovskite Mg2CO3(OH)2 in the rosasite structure and Mg analogues of monoclinic and orthorhombic forms of malachite determine that the octahedral sites are innately distorted, and that d9 Cu(II) Jahn-Teller distortion accommodates this distortion rather than causes it, leading to the significant preference of Cu for the type I octahedral sites. This distortion also leads to a high propensity for formation of cation vacancies charge balanced by proton substitution. Ab initio thermodynamics is used to determine that there are conditions under which proton substitution defects are slightly more stable than the stoichiometric structure, consistent with the widespread observation of such defects in pokrovskite in nature. Pokrovskite itself is most likely to form under CO2-rich/low water conditions, particularly those utilizing supercritical CO2 for carbon sequestration and is sufficiently thermodynamically stable to trap CO2 under geological conditions. Low temperature and high water concentration promotes the formation of proton substitution defects, which has implications for synthesis of any material where octahedral strain may be relieved by proton substitution defects.

Paradsasvarite (IMA No. 2012-077) was found in the Nagy-Lapafő area, Paradsasvar, Matra Mountains, Hungary. It forms pale beige, globular aggregates up to 0.2 mm in diameter on calcite. Associated secondary minerals are smithsonite, hemimorphite, hydrozincite, aurichalcite and rosasite. The mineral was formed as an alteration product of sphalerite and chalcopyrite in a carbonate-rich environment. Paradsasvarite is translucent with a weakly vitreous, dull or silky lustre and white streak. Its Mohs hardness is about 2–3, cleavage and parting were not observed. It is brittle; the fracture is finely fibrous. Average of nine electron-microprobe analyses gave ZnO 58.08, CuO 12.60, PbO 1.27, CO2 (calc.) 19.50, H2O (calc.) 7.94, total 99.39 wt.%, corresponding to the empirical formula (Zn0.62Cu0.36Pb0.01)Σ0.99Zn1.00(CO3)(OH)2. The seven strongest lines in the X-ray powder diffraction pattern are [dhkl in A (Iobs %, hkl)] 6.054 (67, 200), 5.085 (100, 210), 3.703 (87, 310 and 220), 3.021 (25, 400 and 130), 2.971 (25, −211 and 001), 2.603 (62, −221) and 2.539 (36, 420). According to its X-ray powder diffraction data and chemical formula, paradsasvarite belongs to the malachite-rosasite group and it is isostructural with rosasite. It is monoclinic, space group P21/a, a = 12.92(1), b = 9.372(7), c = 3.159(4) A, β = 110.4(1)°, V = 358.5(5) A3, Z = 4.

The crystal structure of kolwezite, (Cu, Co)2(CO3)(OH)2, was refined by Rietveld method from synchrotron X-ray powder data to Rp =4.56%, wRp =6.51%. Kolwezite, P21/a, a= 12.201(1), b=9.354(1), c=3.1494(3)A , b = 98.922(7)°, is isostructural with rosasite. Because of the Jahn-Teller effect, the Me1 polyhedron hosting Cu2þ only is strongly distorted towards a (4þ2) coordination, while the Me2 octahedron, with major Co, is neatly a more regular one. The Me2þ polyhedra are connected through edge-sharing, forming "ribbons" running along [0 0 1] direction. These ribbons are interconnected by corner sharing to form "corrugated" layers, interlinked by the carbonate groups, giving rise to an infinite framework structure, with notationMM=MT. The Rietveld study of synchrotron X-ray powder data of synthetic cobaltoan malachites shows a decrease in unit-cell volume, with an anisotropic contraction of unit-cell parameters, with increasing Co content. The major progressive shortening of apical bonds in Me2 octahedra, with consequent regularization of the Jahn-Teller distorted Cu octahedra, drives a progressive compaction of the malachite structure; it is the main factor accounting for volume contraction in cobaltoan malachites.

Selective conversion of 5-hydroxymethylfurfural (HMF) can produce sustainable fuels and chemicals. Herein, Cu–ZnO catalysts derived from minerals (malachite, rosasite and aurichalcite) were employed for selective hydrogenation of HMF for the first time. High yields of 2,5-dihydroxymethylfuran (~99.1%) and 2,5-dimethylfuran (~91.8%) were obtained tunably over the catalyst with a Cu/Zn molar ratio of 2, due to the well-dispersed metal sites tailored by mineral precursors, well-controlled surface sites and optimized reaction conditions. The relationship between catalytic performance and catalyst properties was elucidated by characterization based on the composition and the structural and surface properties, and catalytic tests. The catalyst can also be extended to selective hydrogenation of other bio-derived molecules (furfural and 5-methylfurfural) to target products. The construction of mineral-derived Cu–ZnO catalysts and the revelation of the structure–performance relationship can be applied to further rational design and functionalization of non-noble Cu catalysts for selective conversion of bio-derived compounds.

Ternary Cu/ZnO/Al2O3 catalyst systems were systematically prepared by innovative synthesis routes in microstructured synthesis setups, allowing to study different types of micromixers. The coprecipitation in the slit plate and valve-assisted mixers was operated continuously under exact control of pH, temperature, concentration and ageing time. Due to the enhanced surface to volume ratio in microstructured reactors, a precise temperature control and efficient mixing of the reactants are enabled. The precipitation was performed with sodium, ammonium and potassium carbonate as well as sodium hydroxide. To evaluate the potential of the novel synthesis routes, reference samples in a conventional batch process were prepared. The catalysts were synthesized according to the constant pH method with a molar ratio of 60:30:10 for copper, zinc and aluminum. The synthesis routes applied have a significant influence on the structures of hydroxycarbonate precursors and on the catalytic activity in methanol synthesis. XRD patterns of hydroxycarbonate precursors from the synthesis in micromixers, especially using ammonium carbonate as precipitating agent, display high crystallinity and sharp reflections of malachite and rosasite. Cu/ZnO/Al2O3 catalysts prepared in continuously operated micromixers in general show higher specific copper surface areas than catalysts prepared in conventional batch processes. The highest methanol productivity of all prepared catalyst systems was observed with the catalyst precipitated in the slit plate mixer with ammonium carbonate. (C) 2012 Published by Elsevier B.V.

Hydroxycarbonates with the general formula Me2(CO3)(OH)2 are widely used materials in industrial processes and are widespread in nature. The Cu term, malachite, Cu2CO3(OH)2, is monoclinic, P21/a. Substitution of Cu2+ with other bivalent cations such as Mg, Zn, Fe, Cu or Ni is possible and leads to a different structure type, rosasite, P21/a or P21/b11 in the same cell setting as malachite. Rosasite structure is topologically similar to malachite, but the symmetry elements are oriented differently with respect to structural units. The stability of the malachite-like structure (MS) compared with the rosasite-like structure (RS) has been suggested to be related to the Jahn–Teller effect in CuO6 coordination polyhedra. For this reason the hypothesis of the phase transition of malachite, Cu2CO3(OH)2, to a rosasite structure at high pressure, as a result of the reduced Jahn–Teller effect, has been tested and confirmed by powder and single-crystal diffraction structural studies: above 6 GPa the malachite structure is no longer stable and transforms to a RS structure. RS Cu2CO3(OH)2 is 3% more dense than malachite and the bulk modulus is remarkably higher, 80 (2) GPa compared with 48 (4) GPa. The longer apical Cu—O bonds in the distorted Me1 octahedral site are progressively shortened with increasing pressure, revealing a decrease in the Jahn–Teller effect at high pressure. The transition has a first-order character, is reversible with a significant hysteresis, and there is no evidence of any intermediate phase between the two structures. We then have further evidence that in the Me2(CO3)(OH)2 compounds, the two main structural types, MS and RS, are closely related. The former structure is stabilized only when Cu is the prevalent cation in the octahedral sites, and it can transform directly to the RS as a function of thermodynamic changes.

The relative stabilities of the copper/zinc solid solutions of hydroxyl sulphates, carbonates, nitrates, chlorides and bromides were studied by attempting their preparation using a variety of methods. All of the naturally occurring solid solutions except rosasite were obtained as single phases. Rosasite crystallized in a mixture with malachite and calcium carbonate during a room temperature preparation from calcium carbonate, copper nitrate and zinc nitrate. The solid solution with the antlerite stoichiometry [endmember Cu3SO4(OH)4] as well as the nitrates were not produced by the methods employed. All of the natural polymorphs of Cu2(OH)3Cl were obtained and a new method for the preparation of botallackite is reported. Botallackite was found to be stable in solution for over a year, contrary to previous reports. A bromine-bearing analogue of botallackite was prepared. Compounds were characterized by X-ray diffractometry, which was used to determine the unit-cell parameters, and by atomic absorption spectroscopy. The relative instability of solid solutions with certain stoichiometries is discussed in terms of the Jahn-Teller effect and relative solubilities.

The Cu/ZnO system is a model for Cu/ZnO/Al2O3 catalysts, which are employed industrially for the synthesis of methanol. These catalysts are usually prepared from mixed basic carbonate precursors. A complex phase mixture, with constituents structurally related to the minerals rosasite andaurichalcite, is present at the industrially applied composition (Cu/Zn ≈ 70:30). Using minerals and phase-pure synthetic samples as references, a comprehensive characterisation of such a phase mixture, including the determination of the individual compositions of the different phases, has been attempted by complementary analytical laboratory techniques (XRD, TGA, IR). The results are critically discussed in light of the complexity of the system. A thermally very stable carbonate species ― well-known for mixed synthetic systems ― is also detected for the mineral reference samples. Significant amounts of amorphous phases are found to be present in the synthetic zincian malachite sample but not in synthetic aurichalcite or the catalyst precursor. A simplified explanation for the shift of the characteristic 20 reflection of the malachite structure as a function of Zn incorporation based on the varying average Jahn–Teller distortion of the MO6 octahedra is proposed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Minerals in the rosasite mineral group namely rosasite, glaucosphaerite, kolwezite, mcguinnessite, nullaginite and pokrovskite have been studied by Raman spectroscopy at 298 and 77 K and complimented with infrared spectroscopy. The spectral patterns for the minerals rosasite, glaucosphaerite, kolwezite and mcguinnessite are similar to that of malachite implying the structure is the same as malachite i.e. monoclinic. A comparison is made with the spectra of malachite. The symmetry of the carbonate anion in the rosasite mineral group is C2v or Cs and is composition dependent. Two (CO3)2- symmetric stretching modes are observed for the rosasite minerals at 1060 and 1090 cm-1. Two hydroxyl stretching modes are observed for the rosasite mineral group. The position of these bands is determined to be a function of the hydrogen bond lengths. Hydrogen bond distances for rosasite are calculated as 2.867, 2.799 and 2.780 A whereas for pokrovskite the distances are 3.280 and 2.999 A. The effect of lowering the temperature from ambient to 77 K results in a decrease of the hydrogen bond distances by 5%. Multiple Raman bands are observed in the 800 to 850 cm-1 and the 720 to 750 cm-1 regions and are attributed to ν2 and ν4 bending modes confirming the reduction of the carbonate anion in the rosasite structure.

This paper presents the mineralization of five medium-size limestone-caves and eleven skarn-hosted caves from the upper part of Cri?ul B¾ isei River (Bihor Mountains). Apart from berlinite - AlPO4, the other minerals reported from the limestone caves are common carbonates, phosphates or oxy- hydroxides. In turn, the skarn-hosted caves contain a diversity of minerals, including wittichenite, luzonite, natrolite, norsethite, rosasite, glaukosphaerite, aurichalcite, azurite, malachite and chalcanthite. Five of these minerals have never before been identified in a cave environment and moreover, three are new occurrences in Romania. Some of these minerals are hydrothermal in origin, whereas alteration and/or hydration of primary hydrothermal minerals formed the others. Considering the mineral assemblage, the morphology and the position of cavities within the skarn bodies, we assume these minerals formed during one of the following stages: hydrothermal, hydrothermal/vadose or vadose.

The crystal structures of malachite Cu2(OH)2CO3 and rosasite (Cu,Zn)2(OH)2CO3, though not isotypic, are closely related. A previously proposed approach explaining this relation via a common hypothetical parent structure is elaborated upon on the basis of group–subgroup considerations, leading to the conclusion that the aristotype of malachite and rosasite should crystallize in the space group Pbam (No. 55). An ICSD database search for actual representatives of this aristotype leads to the interesting observation that the structure type of ludwigite (Mg,Fe)2FeO2BO3, which is adopted by several natural and synthetic oxide orthoborates M 3O2BO3, is closely related to the proposed malachite–rosasite aristotype and thus to the malachite–rosasite family of hydroxide carbonates M 2(OH)2CO3 in general. Relations within both structure families and their analogies are summarized in a joint simplified Bärnighausen tree.

In the present paper we report combined experimental and theoretical studies of the UV-vis-NIR spectra of the mineral compounds malachite, rosasite, and aurichalcite and of the precursor compounds for Cu/ZnO catalysts. For the copper species in the minerals the crystal field splitting and the vibronic coupling constants are estimated using the exchange charge model of the crystal field accounting for the exchange and covalence effects. On this basis the transitions responsible for the formation of the optical bands arising from the copper centers in minerals are determined and the profiles of the absorption bands corresponding to these centers are calculated. The profiles of the absorption bands calculated as a sum of bands of their respective Cu species are in quite good agreement with the experimental data. In agreement with crystal chemical considerations, the Zn ions were found to be preferentially located on the more regular, i.e., less distorted, octahedral sites in zincian malachite and rosasite, suggesting a high degree of metal ordering in these phases. This concept also applies for the mineral aurichalcite, but not for synthetic aurichalcite, which seems to exhibit a lower degree of metal ordering. The catalyst precursor was found to be a mixture of zincian malachite and a minor amount of aurichalcite. The best fit of the optical spectrum is obtained assuming a mixture of contributions from malachite (0% Zn) and rosasite (38% Zn of [Zn + Cu]), which is probably due to the intermediate Zn content of the precursor (30%).

Synthetic zincian malachite samples (Cu1–xZnx)2(OH)2CO3 with x = 0, 0.1, 0.2 and 0.3 were characterized by powder X-ray diffraction and optical spectroscopy. The XRD patterns of the samples up to x = 0.2 indicate single phase materials with an approximately linear dependence of the refined lattice parameters on the zinc content. In contrast, the sample with a nominal zinc content x = 0.3 shows the formation of a small amount of aurichalcite (Zn,Cu)5(OH)6(CO3)2 as an additional phase. Based on the lattice parameter variations, the zinc content of the zincian malachite component in this sample is estimated to be x ≈ 0.27, which seems to represent the maximum possible substitution in zincian malachite under the synthesis conditions applied. The results are discussed in relation to preparation of Cu/ZnO catalysts and the crystal structures of the minerals malachite and rosasite. One striking difference between these two structurally closely related phases is the orientation of the Jahn–Teller elongated axes of the CuO6 octahedra in the unit cell, which seems to be correlated with the placement of the monoclinic β angle. The structural and chemical relationship between these crystallographically distinct phases is discussed using a hypothetical intermediate Zn2(OH)2CO3 phase of higher orthorhombic symmetry. In addition to the crystallographic analysis, optical spectroscopy proves to be a useful tool for estimation of the Cu:Zn ratio in (Cu1–xZnx)2(OH)2CO3 samples.

Minerals in the rosasite group namely rosasite, glaucosphaerite, kolwezite, mcguinnessite have been studied by a combination of infrared and Raman spectroscopy. The spectral patterns for the minerals rosasite, glaucosphaerite, kolwezite and mcguinnessite are similar to that of malachite implying the molecular structure is similar to malachite. A comparison is made with the spectrum of malachite. The rosasite mineral group is characterised by two OH stretching vibrations at approximately 3401 and 3311 cm-1. Two intense bands observed at approximately 1096 and 1046 cm-1 are assigned to nu1(CO3)2- symmetric stretching vibration and the delta OH deformation mode. Multiple bands are found in the 800-900 and 650-750 cm-1 regions attributed to the nu2 and nu4 bending modes confirming the symmetry reduction of the carbonate anion in the rosasite mineral group as C2v or Cs. A band at approximately 560 cm-1 is assigned to a CuO stretching mode.

The crystal structures of glaukosphaerite (Cu,Ni)2(CO3)(OH)2 and pokrovskite Mg2(CO3)(OH)2, two carbonates belonging to the malachite-rosasite group, have been determined from powder diffraction data, and refined up to wRp = 3.94% and 1.63% respectively. Both minerals are isostructural with rosasite (Cu,Zn)2(CO3)(OH)2, with P 21/ a space group and cell parameters a =12.0613(4) A, b = 9.3653(4), c = 3.1361(1), β = 98.085(5)° for glaukosphaerite and a = 12.2396(4), b = 9.3506(4), c = 3.1578(1), β = 96.445(5)° for pokrovskite. Their structures are built up by ribbons of edge-sharing octahedra running along the c -axis; the ribbons are linked together through corner-sharing giving rise to corrugated layers parallel to (100) that are interconnected through carbonate groups. The same layers and carbonate groups, arranged in a different orientation with respect to the symmetry operators, build up the structure of malachite: the relationships between the rosasite-like and the malachite-like structural models are discussed. The octahedral distortion of the two independent Me sites in the malachite-rosasite known structures is evaluated and attributed to the Jahn-Teller effect of Cu2+. According to the available chemical data for the examined material, a partial occupancy in Mg sites of pokrovskite is maintained, with a coupled partial substitution of hydroxyls by water molecules. On the basis of the structural results, the difficulties and ambiguities in the powder pattern indexing by preceeding authors are discussed and explained, and reliable guesses for the arrangements of kolwezite and nullaginite are drawn.

SummaryGlaukosphaerite, a new secondary basic copper-nickel carbonate was first determined and described from Widgiemooltha (31° 30′ S., 121° 34′ E.), Western Australia, by R. C. Morris at the W.A. Government Chemical Laboratories in 1967. The mineral has since been found at the nickel mines at Kambalda, Windarra, Scotia, Carr Boyd Rocks, and St. Ives, Western Australia, and is apparently an indicator of copper-nickel sulphide mineralization. The name is derived from the colour and spherulitic formation. Associated minerals are goethite, secondary quartz, paratacamite, gypsum, nickeloan varieties of magnesite and malachite, and clays. Glaukosphaerite also fills joints in fresh basic rocks.The type material is from Hampton East Location 48, 3 km N. of the Durkin Shaft, Kambalda. Glaukosphaerite is monoclinic, a 9·34 Å, b 11·93 Å, c 3·07 Å, β 90–1°, space group indeterminate, c axis disordered, six strongest X-ray powder lines are 2·587 (10b) 201, 3·68(7b) 220, 2·516(4) 240, 211, 5·04(3) 120, 2·124(3b), 1·473(3). The mineral occurs in green spherules of fibres cleaved and elongated along c, D = 3·78 to 3·96 increasing with Cu, is brittle, H. 3 to 4, and has dull to subvitreous to silky lustre.α 1·69–1·71 green, β ≈ γ 1·83–1·85 yellow-green, α:[001] 7°.Chemical analysis on the type material, D 3·78, containing 0·5 % goethite impurity and minimal inseparable malachite, gave CuO 41·57, NiO 25·22, CoO 0·07, ZnO 0·02, Fe2O3 0·47, MgO 1·23, SiO2 < 0·01, CO2 21·70, H2O+ 9·85, H2O− < 0·01, sum 100·13%. After deduction of goethite the unit cell contains 4[(Cu,Ni,Mg,Co)1.74C0·96H2·12O4·73]. This unit-cell content is deficient in metal ions and oxygen and contains excess H, when compared to 4[(Cu,Ni)2(OH)2CO3]. Two analyses of malachite-bearing glaukosphaerite from Widgiemooltha and Carr Boyd Rocks show the same deficiencies and excess not previously recorded in malachite, rosasite, or aurichalcite analyses. Glaukosphaerite, 4[(Cu,Ni)2(OH)2CO3] is the nickel analogue of rosasite 4[(Cu,Zn)2(OH)2CO3].From results based on X-ray rotation patterns of oriented rosasite fibres from Sardinia and Durango with supplementary electron-microprobe studies and Guinier powder-film data, the authors consider glaukosphaerite and rosasite to be separate mineral species from the related malachite, 4[Cu2(OH)2CO3].Type material is preserved in the government collection at the Government Chemical Laboratories, Perth, Western Australia.

SummaryRosasite and aurichalcite occur with other copper, zinc, and also lead minerals in Masson Cavern, Rutland Cavern, and other workings in the Heights of Abraham, Matloek Bath, Derbyshire. Partial analyses of two specimens each of rosasite and aurichalcite show Cu : Zn ratios typical of the respective species. They appear to have been formed by the action of solutions containing zinc on disseminated chalcopyrite. The infra-red absorption spectra of malachite, rosasite, aurichalcite, and hydrozincite, examined by the mull technique, are shown to fall into two groups corresponding with the structural groups established by X-ray work. Twin absorption maxima at O-H stretching frequencies are present in the spectra of malachite and of rosasite.

The stabilities of rosasite, (Cu, Zn)2 (CO3)(OH)2, and aurichalcite, (Zn, Cu)5(CO3)2(OH)6, have been determined by solution experiments with computer calculations of aqueous species in equilibrium with the solid phases. ΔG f o values for rosasite and aurichalcite have been calculated as −1100 and −2766 kJ mol−1 respectively for specific samples of the two minerals. Most of the difference between the free energies of the compounds and those of malachite, Cu2(CO3)(OH)2, and hydrozincite, Zn5(CO3)2(OH)6 arises from substitution of the minor cation in the crystal lattice. Malachite, zincian malachite and rosasite should be considered as a single isomorphous series.