A vibrational spectroscopic study of the phosphate mineral Wardite NaAl3(PO4)2(OH)4•2(H2O)

Three wardite mineral samples from different origins have been analysed by vibrational spectroscopy. The mineral is unusual in that it belongs to a unique symmetry class, namely the tetragonal-trapezohedral group. The structure of wardite contains layers of corner-linked –OH bridged MO6 octahedra stacked along the tetragonal C-axis in a four-layer sequence and linked by PO4 groups. Consequentially not all phosphate units are identical. Thus, two intense Raman bands observed at 995 and 1051 cm-1 are assigned to the ν1 PO43- symmetric stretching mode. Intense Raman bands are observed at 605 and 618 cm-1 with shoulders at 578 and 589 cm-1 are assigned to the ν4 out of plane bending modes of the PO43-. The observation of multiple bands supports the concept of non-equivalent phosphate units in the structure. Sharp infrared bands are observed at 3544 and 3611 cm-1 are attributed to the OH stretching vibrations of the hydroxyl units. Vibrational spectroscopy enables subtle details of the molecular structure of wardite to be determined.

Is the mineral borickyite (Ca,Mg)(Fe3+,Al)4(PO4,SO4,CO3)(OH)8•3-7.5H2O the same as delvauxite CaFe3+4(PO4,SO4)2(OH)8•4-6H2O?

The two minerals borickyite and delvauxite CaFe3+4(PO4,SO4)2(OH)8•4-6H2O have the same formula. Are the minerals identical or different? The minerals borickyite and delvauxite have been characterised by Raman spectroscopy. The minerals are related to the minerals diadochite and destinezite. Both minerals are amorphous. Delvauxite appears to vary in crystallinity from amorphous to semi-crystalline. The minerals are often X-ray non-diffracting. The minerals are found in soils and may be described as ‘colloidal’ minerals. Vibrational spectroscopy enables an assessment of the molecular structure of borickyite and delvauxite. Bands are assigned to phosphate and sulphate stretching and bending modes. Multiple water bending and stretching modes imply that non-equivalent water molecules in the structure exist with different hydrogen bond strengths. The two minerals show differing spectra and must be considered as different minerals.

Identification of montgomeryite mineral [Ca4MgAl4(PO4)6.(OH)4•12H2O] found in the Jenolan Caves - Australia

In this paper, we report on many phosphate containing natural minerals found in the Jenolan Caves - Australia. Such minerals are formed by the reaction of bat guano and clays from the caves. Among these cave minerals is the montgomeryite mineral [Ca4MgAl4(PO4)6.(OH)4.12H2O]. The presence of montgomeryite in deposits of the Jenolan Caves - Australia has been identified by X-ray diffraction (XRD). Raman spectroscopy complimented with infrared spectroscopy has been used to characterize the crystal structure of montgomeryite. The Raman spectrum of a standard montgomeryite mineral is identical to that of the Jenolan Caves sample. Bands are assigned to H2PO4-, OH and NH stretching vibrations. By using a combination of XRD and Raman spectroscopy, the existence of montgomeryite in the Jenolan Caves - Australia has been proven. A mechanism for the formation of montgomeryite is proposed.

Raman spectroscopy of synthetic CaHPO4•2H2O– and in comparison with the cave mineral brushite

The mineral brushite has been synthesised by mixing calcium ions and hydrogen phosphate anions to mimic the reactions in a Cave. The vibrational spectra of the synthesised brushite were compared with that of the natural Cave mineral. Bands attributable to the PO43- and HPO42- anions are observed. Brushite, both synthetic and natural, is characterised by an intense sharp band at 985 cm-1 with a shoulder at 1000 cm-1. Characteristic bending modes are observed in the 300 to 600 cm-1 region. The spectra of the synthesised brushite matches very well the spectrum of brushite from the Moorba Cave, Western Australia.

Vibrational spectroscopic study of multianion mineral clinotyrolite Ca2Cu9[(As,S)O4]4(OH)10•10(H2O)

The molecular structure of the mixed anion mineral Clinotyrolite Ca2Cu9[(As,S)O4]4(OH)10•10(H2O) has been determined by the combination of Raman and infrared spectroscopy. Characteristic bands associated with arsenate, sulphate and hydroxyl units are identified. Broad bands in the OH stretching region are observed and are resolved into component bands. Estimates of hydrogen bond distances were made using a Libowitzky function and both short and long hydrogen bonds are identified. Two intense Raman bands at 842 and ~796 cm-1 are assigned to the ν1 (AsO4)3- symmetric stretching and ν3 (AsO4)3- antisymmetric stretching modes. The comparatively sharp Raman band at 980 cm-1 is assigned to the ν1 (SO4)2- symmetric stretching mode and a broad Raman spectral profile centred upon 1100 cm-1 is attributed to the ν3 (SO4)2- antisymmetric stretching mode.

Vibrational spectroscopic study of the copper silicate mineral ajoite (K,Na)Cu7AlSi9O24(OH)6•3H2O

Ajoite (K,Na)Cu7AlSi9O24(OH)6•3H2O is a mineral named after the Ajo district of Arizona. Raman and infrared spectroscopy were used to characterise the molecular structure of ajoite. The structure of the mineral shows disorder which is reflected in the difficulty of obtaining quality Raman spectra. The Raman spectrum is characterised by a broad spectral profile with a band at 1048 cm-1 assigned to the ν1 (A1g) symmetric stretching vibration. Strong bands at 962, 1015 and 1139 cm-1 are assigned to the ν3 SiO4 antisymmetric stretching vibrations. Multiple ν4 SiO4 vibrational modes indicate strong distortion of the SiO4 tetrahedra. Multiple AlO and CuO stretching bands are observed. Raman spectroscopy and confirmed by infrared spectroscopy clearly shows that hydroxyl units are involved in the ajoite structure. Based upon the infrared spectra, water is involved in the ajoite structure, probably as zeolitic water.

Raman spectroscopy of the borate mineral ameghinite NaB3O3(OH)4

The molecular structure of the sodium borate mineral ameghinite NaB3O3(OH)4 has been determined by the use of vibrational spectroscopy. The crystal structure consists of isolated [B3O3(OH)4]- units formed by one tetrahedron and two triangles. H bonds and Na atoms link these polyanions to form a 3-dimensional framework. The Raman spectrum is dominated by an intense band at 1027 cm-1, attributed to BO stretching vibrations of both the trigonal and tetrahedral boron. A series of Raman bands at 1213, 1245 and 1281cm-1 are ascribed to BOH in-plane bending modes. The infrared spectra are characterized by strong overlap of broad multiple bands. An intense Raman band found at 620 cm-1 is attributed to the bending modes of trigonal and tetrahedral boron. Multiple Raman bands in the OH stretching region are observed at 3206, 3249 and 3385 cm-1. Raman spectroscopy coupled with infrared spectroscopy has enabled aspects about the molecular structure of the borate mineral ameghinite to be assessed.

Vibrational spectroscopic study of the mineral creaseyite Cu2Pb2(Fe,Al)2(Si5O17)·6H2O – a zeolite mineral?

Vibrational spectroscopy has been used to characterise the mineral creaseyite Cu2Pb2(Fe,Al)2(Si5O17)·6H2O. The mineral is found in the oxidised zone of base metal deposits and interestingly is associated with copper silicate minerals including ajoite, kinoite, chrysocolla as well as wulfenite, willemite, mimetite and wickenburgite. Creaseyite is a mineral with zeolitic properties. A Raman band at 998 cm−1 is assigned to the SiO stretching vibration of SiO3 units. The Raman band at 1071 cm−1 is assigned to the SiO stretching vibrations of the Si2O5 units. Raman bands are found at 2750, 2902, 3162, 3470 and 3525 cm−1. The band at 3525 cm−1 is attributed to zeolitic water. Other bands are assigned to water coordinated to the metal cations. Vibrational spectroscopy enables aspects of the molecular structure of creaseyite to be determined.

Molecular structure of the mineral svanbergite SrAl3(PO 4,SO4)2(OH)6 - A vibrational spectroscopic study

The mineral svanbergite SrAl 3(PO 4,SO 4) 2(OH) 6 is a hydroxy phosphate-sulphate mineral belonging to the beudantite subgroup of alunites and has been characterised by vibrational spectroscopy. Bands at various wavenumbers were assigned to the different vibrational modes of svanbergite, which were then associated with the structure of the mineral. Bands were primarily assigned to phosphate and sulphate stretching and bending modes. Two symmetric stretching modes for both phosphate and sulphate supported the concept of non-equivalent phosphate and sulphate units in the mineral structure. Bands in the OH stretching region enabled hydrogen bond distances to be calculated. Comparison of the hydrogen bond distances and the calculated hydrogen bond distances from the structure models indicates that hydrogen bonding in svanbergite occurs between the two OH units rather than OH to SO42- units.

Raman spectroscopic study of the mineral xonotlite Ca 6Si 6O 17(OH) 2-A component of plaster boards

The mineral xonotlite Ca 6Si 6O 17(OH) 2 is a crystalline calcium silicate hydrate which is widely used in plaster boards and in many industrial applications. The structure of xonotlite is best described as having a dreierdoppelketten silicate structure, and describes the repeating silicate trimer which forms the silicate chains, and doppel indicating that two chains combine. Raman bands at 1042 and 1070 cm -1 are assigned to the SiO stretching vibrations of linked units of Si 4O 11 units. Raman bands at 961 and 980 cm -1 serve to identify Si 3O 10 units. The broad Raman band at 862 cm -1 is attributed to hydroxyl deformation modes. Intense Raman bands at 593 and 695 cm -1 are assigned to OSiO bending vibrations. Intense Raman bands at 3578, 3611, 3627 and 3665 cm -1 are assigned to OH stretching vibrations of the OH units in xonotlite. Infrared spectra are in harmony with the Raman spectra. Raman spectroscopy with complimentary infrared spectroscopy enables the characterisation of the building material xonotlite.

Mineralogy of chondritic interplanetary dust particles

From a mineralogical survey of approximately 30 chondritic micrometeorites collected from the lower stratosphere and studied in detail using current electron microscopy techniques, it is concluded that these particles represent a unique group of extraterrestrial materials. These micrometeorites differ significantly in form and texture from components of carbonaceous chondrites and contain some mineral assemblages which do not occur in any meteorite class. Electron microscope investigations of chondritic micrometeorites have established that these materials (1) are extraterrestrial in origin, (2) existed in space as small objects, (3) endured minimal alteration by planetary processes since formation, and (4) can suffer minimal pulse heating (<600°C) on entering earth's atmosphere. The probable sources for chondritic interplanetary dust particles (IDPs) are cometary and asteroidal debris and, perhaps to a lesser extent, interstellar regions. These sources have not been conclusively linked to any specific mineralogical subset of IDP, although the chondritic porous (CP) aggregate is considered of likely cometary origin. Chondritic IDPs occur in two predominant mineral assemblages: (1) carbonaceous phases and phyllosilicates and (2) carbonaceous phases and nesosilicates or inosilicates, although particles with both types of silicate assemblages are observed. Olivines, pyroxenes, layer silicates, and carbon-rich phases are the most commonly occurring minerals in many chondritic IDPs. Other phases often observed in variable proportions include sulphides, spinels, metals, metal carbides, carbonates, and minor amounts of sulphates and phosphates. Individual mineral grain sizes range from micrometers (primarily pyroxenes and olivines) to nanometers, with the predominant size for all phases less than 100 nm. Specific mineral characteristics for particular chondritic IDPs provide an indication of processes which may have occurred prior to collection in the earth's stratosphere. For example, pyroxene mineralogy in some chondritic aggregates is consistent with condensation from a vapor phase and, we consider, with condensation in a turbulent solar nebula at relatively low temperatures (<1000°C). Carbonaceous phases present in other CP aggregates have been used to imply low-temperature formation processes such as Fischer-Tropsch synthesis (∼530°C) or carbonization and graphitization (∼315°C). Alteration processes have been implicated in the formation of some layer silicates in CP aggregates and may have involved hydrocryogenic alteration at <0°C. In general, interpretations of transformation processes on submicrometer-size minerals in chondritic IDPs are consistent with formation at a radius equivalent to the asteroid belt or greater during the later stages of solar nebula evolution using currently available models.

Mineralogy of chondritic porous aggregates : current status

Chondritic porous aggregates (CPA's) belong to an important subset of small particles (usually between 5 and 50 micrometers) collected from the stratosphere by high flying aircraft. These aggregates are approximately chondritic in elemental abundance and are composed of many thousands of small­er, submicrometer particles. CPA particles have been the subject of intensive study during the past few years [1-3] and there is strong evidence that they are a new class of extraterrestrial material not represented in the meteorite collection [3,4]. However, CPA's may be related to carbonaceous chondrites and in fact, both may be part of a continuum of primitive extraterrestrial materials [5]. The importance of CPA's stems from suggestions that they are very primitive solar system material possibly derived from early formed proto­ planets, chondritic parent bodies, or comets [3, 6]. To better understand the origin and evolution of these particles, we have attempted to summarize all of the mineralogical data on identified CPA's published since about 1976.

A multi-stage history for carbonaceous material in extraterrestrial chondritic porous aggregate W7029*A and a new cosmothermometer

A new set of primitive extraterrestrial materials collected in the Earth's stratosphere include Chondritic Porous Aggregates (CPA's) [1]. CPAs have a complex and variable mineralogy [1-3] that include 'organic compounds' [4,5] and poorly graphitised carbon (PGC)[6]. This study presents a continuation of our detailed Analytical Electron Microscope study on carbon-rich CPA W7029*A from the JSC Cosmic Dust Collection. This CPA is an uncontaminated sample that survived atmospheric entry without appreciable alteration [7] and which contains ~44% carbonaceous material. The carbonaceous composition of selected particles was confirmed by Electron Energy Loss Spectroscopy and Selected Area Electron Diffraction (SAED). Possible carbonaceous contaminants introduced by specimen preparation techniques are easily recognised from indigenous CPA carbon particles [8] and do not bias our interpretations.

Diagenesis in interplanetary dust - chondritic porous aggregate w7029-star-a

In previous Analytical Electron Microscope studies of extraterrestrial Chondritic Porous Aggregate (CPA) W7029* A, we have reported on the presence of layer silicates(Rietmeijer and Mackinnon, 1984a; Mackinnon and Rietmeijer, 1983) and metal oxides (Rietmeijer and Mackinnon, 1984a; Mackinnon and Rietmeijer, 1984). We present here a continuation ofthis detailed mineralogical study and propose a scenario which may account for the variety and types of phases observed in this CPA. At least 50% ofCPA W7029*A is carbonaceous material, primarily poorly graphitised carbon (POC) with morphologies similar to POC in acid residues of carbonaceous chondrites (Smith and Busek, 1981; Lumpkin, 1983). The basal spacing of graphite in CPA W7029*A ranges from 3.47-3.52 A and compares with doo, of graphite in the Allende residues (Smith and Buseck, 1981; Lumpkin, 1983). Low-temperature phases comprise - 20% of CPA W7029*A and include layer silicates, Bi,O" a-FeOOH(Rietmeijer and Mackinnon, 1984a; Mackinnon and Rietmeijer, 1983), BaSO.,.Ti.O, plates, pentlandite-violarite and bornite. Clusters of Mg-rich olivine and pyroxene make up - 12% of the aggregate...