Combined remote LIBS and Raman spectroscopy at 8.6m of sulfur-containing minerals, and minerals coated with hematite or covered with basaltic dust

Combined remote laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy investigations at a distance of 8.6m have been carried out in air and under a simulated Martian atmosphere of 933Pa (7Torr) CO(2) on calcite (CaCO(3)), gypsum (CaSO(4).2H(2)O), and elemental sulfur (S), and LIBS investigations on chalcopyrite (CuFeS(2)) and pyrite (FeS(2)). Both Raman and LIBS techniques have also been used sequentially in air on hematite-coated calcite crystals and on a sample of anhydrite covered with basaltic dust. These experiments demonstrate that by using a frequency-doubled Nd:YAG pulsed laser co-radiating 1064 nm and 532 nm laser beams with a 5x beam expander, it is possible to measure simultaneously both the Raman and LIBS spectra of calcite, gypsum and elemental sulfur by adjusting the laser power electronically. The spectra of calcite, gypsum, and elemental sulfur contain fingerprint Raman lines; however, it was not possible to measure the remote Raman spectra of pyrite and chalcopyrite because of low intensities of Raman lines. In the cases of CuFeS(2), FeS(2), and elemental sulfur, S atomic emission lines in the LIBS spectra were detected only in 7Torr of CO(2) pressure and not in air. No S atomic emission lines were detected for gypsum in air or in CO(2). In the case of coated/dusted minerals, it was possible to remove the coating or dust with the focused LIBS laser and measure the Raman spectra of subsurface minerals with a 532 nm laser excitation. The complementary nature of these two techniques is highlighted and discussed.     

Raman spectroscopic analysis of minerals and organic molecules of relevance to astrobiology

Characteristic geological features and hydrated minerals recently found on the surface of Mars by the NASA planetary rovers Spirit and Opportunity suggest that a possible biosphere could have once existed there. Analytical instrumentation protocols for the unequivocal detection of biomarkers in suitable geological matrices are critical for future unmanned explorations, including the forthcoming ESA-ExoMars mission scheduled for 2018. Raman spectroscopy is currently a part of the Pasteur instrumentation suite of the ExoMars mission scheduled for 2018 for the remote detection of extant or extinct life signatures in the Martian surface and subsurface. Terrestrial analogues of Martian sites have been identified, and the biogeological modifications incurred as a result of extremophilic survival activity have been studied. Polyaromatic hydrocarbons (PAHs) are recognised as a class of degradation product that occur from biological processes terrestrially. In this work, various concentrations of polyaromatic hydrocarbons in matrices of gypsum, calcite and quartz have been investigated by Raman microspectrometry to determine the lowest detectable organic levels. The studies are conceived in simulation of their potential PAHs identification in geobiological conditions in Martian scenarios. Two laser source wavelengths, namely, 785 and 633 nm, were adopted to excite Raman spectra from the PAHs, which represent degraded carbons and therefore potentially provide a key bimolecular marker of ancient life.     

Surface hydration of aqueous calcium minerals as studied by Fourier transform Raman and infrared spectroscopy

Rapid hydration reactions of several calcium minerals are studied using Fourier transform (FT) Raman and infrared (IR) spectroscopy. Oleate adsorption over aqueous synthetic fluorite, calcite and gypsum (pH 9) is investigated and adsorption mechanisms are discussed.     

Remote Raman and fluorescence studies of mineral samples

In the present study, we investigated remote laser-induced fluorescence (LIF), at a distance of 4.8 m, of a variety of natural minerals and rocks, and Hawaiian Ti (Cordyline terminalis) plant leaves. These minerals included calcite cleavage, calcite onex and calcite travertine, gypsum, fluorapatite, Dover flint and chalk, chalcedony and nephelene syenite, and rubies containing rock. Pulsed laser excitation of the samples at 355 and 266 nm often resulted in strong fluorescence. The LIF bands in the violet-blue region at approximately 413 and approximately 437 nm were observed only in the spectrum of calcite cleavage. The green LIF bands with band maxima in the narrow range of approximately 501-504 nm were observed in the spectra of all the minerals with the exception of the nephelene syenite and ruby rocks. The LIF red bands were observed in the range approximately 685-711 nm in all samples. Excitation with 532 nm wavelength laser gave broad but relatively low fluorescence background in the low-frequency region of the Raman spectra of these minerals. One microsecond signal gating was effective in removing nearly all background fluorescence (with peak at approximately 610 nm) from calcite cleavage Raman spectra, indicating that the fluorescence was probably from long-lifetime inorganic phosphorescence.     

Identification of β-carotene in an evaporitic matrix—evaluation of Raman spectroscopic analysis for astrobiological research on Mars

Since evaporitic rocks on the Martian surface could (or still can) serve as potential habitats for microbial life on Mars, there is a reasonable possibility that these rocks may sustain molecular remnants as evidence for the presence of extinct or extant living organisms on Mars and that β-carotene could be a suitable biomarker. In this paper, Raman microspectrometry was tested as a nondestructive method of determining the lowest detectable β-carotene content in experimentally prepared evaporitic matrices—namely, gypsum, halite and epsomite. Two excitation wavelengths were compared—514.5 nm, because of the resonance Raman enhancement in the carotenoid analysis, and 785 nm, as a more universal wavelength now much used in the detection of biomolecules terrestrially. Mixtures were measured directly as well as with a laser beam penetrating the crystals of gypsum and epsomite. We have obtained β-carotene signals at the 0.1 to 10 mg kg⁻¹ level—the number of registered β-carotene Raman bands differed depending on the particular mineral matrix and the excitation wavelength. Concentrations of β-carotene of about one order of magnitude higher were identified when analysed through single crystals of gypsum and epsomite, respectively.     

Raman spectroscopy of stercorite H(NH4)Na(PO4)·4H2O--a cave mineral from Petrogale Cave, Madura, Eucla, Western Australia

Raman spectroscopy complimented with infrared spectroscopy has been used to characterise the mineral stercorite H(NH4)Na(PO4)·4H2O. The mineral stercorite originated from the Petrogale Cave, Madura, Eucla, Western Australia. This cave is one of many caves in the Nullarbor Plain in the South of Western Australia. These caves have been in existence for eons of time and have been dated at more than 550 million years old. The mineral is formed by the reaction of bat guano chemicals on calcite substrates. A single Raman band at 920 cm(-1) defines the presence of phosphate in the mineral. Antisymmetric stretching bands are observed in the infrared spectrum at 1052, 1097, 1135 and 1173 cm(-1). Raman spectroscopy shows the mineral is based upon the phosphate anion and not the hydrogen phosphate anion. Raman and infrared bands are found and assigned to PO4(3-), H2O, OH and NH stretching vibrations. The detection of stercorite by Raman spectroscopy shows that the mineral can be readily determined; as such the application of a portable Raman spectrometer in a 'cave' situation enables the detection of minerals, some of which may remain to be identified.     

Raman spectroscopy of some basic chloride containing minerals of lead and copper

Raman spectroscopy has been used to characterise several lead and mixed cationic-lead minerals including mendipite, perite, laurionite, diaboléite, boléite, pseudoboléite, chloroxiphite, and cumengéite. Raman spectroscopy enables their vibrational spectra to be compared. The low wavenumber region is characterised by the bands assigned to cation-chloride stretching and bending modes. Phosgenite is a mixed chloride-carbonate mineral and a comparison is made with the molecular structure of the aforementioned minerals. Each mineral shows different hydroxyl stretching vibrational patterns, but some similarity exists in the Raman spectra of the hydroxyl deformation modes. Raman spectroscopy lends itself to the study of these types of minerals in complex mineral systems involving secondary mineral formation.     

Raman microspectroscopy of organic inclusions in spodumenes from Nilaw (Nuristan, Afghanistan)

The color varieties of spodumene (green spodumene, kunzite) from Nilaw mine (Nuristan, Afghanistan) have been investigated by microthermometry and Raman spectroscopy analyses. These minerals are rich in primary and secondary fluid inclusions. Measured values of temperature homogenization (T(h)) and pressure (P) for selected fluid-inclusion assemblages (I-IV) FIA in green spodumene and (I-II) FIA in kunzite ranges from 370 to 430°C, 1.16 to 1.44 kbar and 300 to 334°C, 0.81 to 1.12 kbar, respectively. The brine content and concentration varies from 4.3 to 6.6 wt.% eq. NaCl. Numerous and diverse mineral phases (quartz, feldspars, mica, beryl, zirconium, apatite, calcite, gypsum) present in this mineral as solid inclusions were studied by Raman microspectroscopy. Raman spectra of selected fluid, organic and solid inclusions were collected as line or rectangular maps and also depth profiles to study their size and contents. There appeared very interesting calcite (156, 283, 711 and 1085 cm(-1)), beryl (324, 397, 686, 1068 and 3610 cm(-1)), topaz (231, 285, 707, 780 and 910 cm(-1)) and spodumene (355, 707 and 1073 cm(-1)) inclusions accompanied by fluid and/or organic inclusions (liquid and gas hydrocarbons) with bands at 2350 cm(-1) (CO(2), N(2)), 2550 cm(-1) (H(2)S) and 2900 cm(-1) (C(2)H(6)-CH(3)). Some solid inclusions contain carbonaceous matter (D-band at ca. 1320 cm(-1) and/or G-band at ca. 1600 cm(-1)).     

Inductively coupled plasma-atomic emission spectrometry method for determination of trace metals in alkaline-earth matrices after flotation separation

An inductively coupled plasma-atomic emission spectrometry (ICP-AES) method is developed for determination of Cd, Co, Cr, Cu, Ni, Tl and Zn in traces in calcite, CaCO₃, dolomite, CaMg(CO₃)₂, and gypsum, CaSO₄. Interferences of a Ca/Mg matrix on analyte intensities were investigated. The results reveal that Ca does not interfere with Cr, Ni and Zn, but tends to decrease the intensity of the other elements. Magnesium as a matrix element does not interfere on with Zn, but increases the intensities of Ni, Cr and Cu, and decreases the intensities of Cd, Co and Tl. To eliminate these matrix interferences on trace element intensities, a flotation separation method is proposed. Lead(II) hexamethylenedithiocarbamate, Pb(HMDTC)₂, is applied as a collector for flotation of trace elements from acidic solutions of mineral samples. The flotation of acidic aqueous solutions of calcite, dolomite and gypsum was performed at pH 6.0, using 10 mg l⁻¹ Pb and 0.3 mmol l⁻¹ HMDTC⁻ added to 1 l of solution tested. The method detection limits of analytes in different minerals range from 0.02 to 0.06 μg g⁻¹ for Cd, 0.04 to 0.10 μg g⁻¹ for Co, 0.03 to 0.13 μg g⁻¹ for Cr, 0.02 to 0.16 μg g⁻¹ for Cu, 0.09 to 0.30 μg g⁻¹ for Ni, 6.45 to 7.71 μg g⁻¹ for Tl and 0.18 to 0.20 μg g⁻¹ for Zn.     

The micro-distribution of carbonaceous matter in the Murchison meteorite as investigated by Raman imaging

The carbonaceous Murchison chondrite is one of the most studied meteorites. It is considered to be an astrobiology standard for detection of extraterrestrial organic matter. Considerable work has been done to resolve the elemental composition of this meteorite. Raman spectroscopy is a very suitable technique for non-destructive rapid in situ analyses to establish the spatial distribution of carbonaceous matter. This report demonstrates that Raman cartography at a resolution of 1 microm2 can be performed. Two-dimensional distribution of graphitised carbon, amorphous carbonaceous matter and minerals were obtained on 100 microm2 maps. Maps of the surface of native stones and of a powdered sample are compared. Graphitic and amorphous carbonaceous domains are found to be highly overlapping in all tested areas at the surface of the meteorite and in its interior as well. Pyroxene, olivine and iron oxide grains are embedded into this mixed carbonaceous material. The results show that every mineral grain with a size of less than a few microm2 is encased in a thin carbonaceous matrix, which accounts for only 2.5 wt.%. This interstitial matter sticks together isolated mineral crystallites or concretions, including only very few individualized graphitised grains. Grinding separates the mineral particles but most of them retain their carbonaceous coating. This Raman study complements recent findings deduced from other spatial analyses performed by microprobe laser-desorption laser-ionisation mass spectrometry (microL2MS), transmission electron microscopy (TEM) and scanning transmission X-ray microscopy (STXM).     

Remote-Raman spectroscopic study of minerals under supercritical CO2 relevant to Venus exploration

The authors have utilized a recently developed compact Raman spectrometer equipped with an 85 mm focal length (f/1.8) Nikon camera lens and a custom mini-ICCD detector at the University of Hawaii for measuring remote Raman spectra of minerals under supercritical CO(2) (Venus chamber, ～102 atm pressure and 423 K) excited with a pulsed 532 nm laser beam of 6 mJ/pulse and 10 Hz. These experiments demonstrate that by focusing a frequency-doubled 532 nm Nd:YAG pulsed laser beam with a 10× beam expander to a 1mm spot on minerals located at 2m inside a Venus chamber, it is possible to measure the remote Raman spectra of anhydrous sulfates, carbonates, and silicate minerals relevant to Venus exploration during daytime or nighttime with 10s integration time. The remote Raman spectra of gypsum, anhydrite, barite, dolomite and siderite contain fingerprint Raman lines along with the Fermi resonance doublet of CO(2). Raman spectra of gypsum revealed dehydration of the mineral with time under supercritical CO(2) at 423 K. Fingerprint Raman lines of olivine, diopside, wollastonite and α-quartz can easily be identified in the spectra of these respective minerals under supercritical CO(2). The results of the present study show that time-resolved remote Raman spectroscopy with a compact Raman spectrometer of moderate resolution equipped with a gated intensified CCD detector and low power laser source could be a potential tool for exploring Venus surface mineralogy both during daytime and nighttime from a lander.     

Spectroscopic study of phase transitions in natural calcite mineral

The process and the formation of new minerals upon heating the carbonate rocks containing clay minerals, together with calcite are determined with thermal analysis, X-ray diffraction, infrared and Raman spectroscopy. The calcite-calcium oxide phase transition sequence was followed up to 947 degrees C in naturally occurring limestone samples. The spectral variations of the internal modes of the carbonate trigonal (nu(1), nu(2), nu(3) and nu(4)) were used to probe the structural phase transitions. The calcium oxide phase (which on reaction with atmospheric water forms portlandite) with an onset temperature of around 950 degrees C was also characterized by the appearance of the infrared mode around 450 cm(-1). The minerals, which were formed upon heating the calcite, were calcium oxide and wollastonite.     

高灰煤中矿物质及碳结构的振动光谱分析

利用傅里叶变换红外光谱(FT-IR)、拉曼光谱和X射线衍射(XRD),分析了广西合山煤(GX)和平顶山煤(PD)及其酸洗煤的矿物质组分和碳结构。FT-IR谱图显示,GX和PD原煤的高岭石含量最为丰富,其次是石英和方解石,由二阶导数红外谱图发现,煤中还存在云母、蛇纹石、石膏和碱性长石。此外,从FT-IR谱图出现的三个层间水OH伸缩振动峰(3 695、3 651和3 619 cm^-1)判断煤中高岭石的结晶度不高。酸洗煤的FT-IR和XRD分别显示出清晰的芳香C=C官能团峰(1 600 cm^-1)和微晶碳(002)衍射峰;原煤的FT-IR和XRD都表明,矿物质完全掩盖了碳的信息。尽管如此,原煤及酸洗煤的拉曼谱图显示出清晰的缺陷碳峰(D峰)和石墨碳峰(G峰),而矿物质的信息完全被信号更强的碳峰掩盖。酸洗处理对煤的碳结构有较弱的影响,酸洗煤的碳结构有序度略低于原煤。     

Taphonomy of prehistoric bark in a salt environment at the archaeological site in Hallstatt,Upper Austria – An analytical approach based on FTIR spectroscopy

Taphonomy of subfossil bark was assessed in Hallstatt, Upper Austria. Samples from the Bronze Age were compared with recent corresponding material from the same site. Preservation of the prehistoric samples was caused by storage in a salt and clay mixture. FTIR spectroscopy was used to determine differences in material chemistry. Principal Component Analysis was applied to display the segregation of the data set according to the different factors and to display the strength of the effects. Results revealed that deacetylation processes dominated aging processes. Focusing on two band regions at around 1730 and 1230 cm⁻¹ a clear separation was achieved. Additionally some samples were selected for further analyses to investigate the influence of the inorganic matrix. Thermal analyses demonstrated an ash content of more than 15%_mass. X-ray diffractometry revealed the presence of salt (dominant), gypsum, pyrite, quartz, and calcite minerals.     

Sulphate efflorescent minerals from El Jaroso Ravine, Sierra Almagrera--An SEM and Raman spectroscopic study

Two sulphate efflorescent evaporite mineral samples from Jaroso, Spain have been studied by scanning electron microscopy and Raman spectroscopy. SEM by comparison with known minerals shows the evaporite mineral is a mixture of halotrichite and jarosite, whilst the oxidised mineral is predominantly jarosite. SEM characterises the halotrichite as long narrow crystals and the jarosite as distorted rhombohedral crystals. Raman spectra of the sulphates of K, Mg, Fe(II), Fe(III) are compared with the spectra of halotrichite, jarosite and the two sulphate efflorescent samples. The efflorescent sample was proven by Raman spectroscopy to be a mixture of halotrichite and jarosite and the oxidised efflorescent sample to be jarosite and a complex mixture of sulphates.     

Ancient biodeterioration: an FT–Raman spectroscopic study of mammoth and elephant ivory

Raman spectra of mammoth ivory specimens have been recorded using near-infrared excitation, and comparisons made with modern Asian and African elephant ivories. Whereas the most ancient mammoth ivory (60–65 ky) showed no evidence for an organic collagen component, more recent samples of mammoth ivory indicated that some preservation had occurred, although with biodeterioration of the protein structure exhibited by the amide I and III bands in the 1200–1700 cm⁻¹ region of the Raman spectrum. The consequent difficulties encountered when applying chemometrics methods to ancient ivory analysis (which are successful for modern specimens) are noted. In the most ancient mammoth ivory specimens, which are extensively fragmented, evidence of mineralization is seen, with the production of gypsum, calcite and limonite; Raman microscopic analysis of crystalline material inside the fissures of the mammoth ivory shows the presence of gypsum as well as cyanobacterial colonisation. The application of Raman spectroscopy to the nondestructive analysis of archaeological materials in order to gain information of relevance to their preservation or restoration is highlighted.     

Vibrational spectroscopic study of the mineral pitticite Fe, AsO4, SO4, H2O

Some minerals are colloidal and show no X-ray diffraction patterns. Vibrational spectroscopy offers one of the few methods for the determination of the structure of these minerals. Among this group of minerals is pitticite, simply described as (Fe, AsO(4), SO(4), H(2)O). In this work, the analogue of the mineral pitticite has been synthesised. The objective of this research is to determine the molecular structure of the mineral pitticite using vibrational spectroscopy. Raman and infrared bands are attributed to the AsO(4)(3-), SO(4)(2-) and water stretching and bending vibrations. The Raman spectrum of the pitticite analogue shows intense peaks at 845 and 837cm(-1) assigned to the AsO(4)(3-) stretching vibrations. Raman bands at 1096 and 1182cm(-1) are attributed to the SO(4)(2-) antisymmetric stretching bands. Raman spectroscopy offers a useful method for the analysis of such colloidal minerals.     

Joint analyses by laser-induced breakdown spectroscopy (LIBS) and Raman spectroscopy at stand-off distances

Raman spectroscopy and laser-induced breakdown spectroscopy (LIBS) of solid samples have both been shown to be feasible with sample-to-instrument distances of many meters. The two techniques are very useful together, as the combination of elemental compositions from LIBS and molecular vibrational information from Raman spectroscopy strongly complement each other. Remote LIBS and Raman spectroscopy spectra were taken together on a number of mineral samples including sulfates, carbonates and silicates at a distance of 8.3 m. The complementary nature of these spectra is highlighted and discussed. A factor of approximately 20 difference in intensity was observed between the brightest Raman line of calcite, at optimal laser power, and the brighter Ca I LIBS emission line measured with 55 mJ/pulse laser power. LIBS and Raman spectroscopy have several obstacles to devising a single instrument capable of both techniques. These include the differing spectral ranges and required detection sensitivity. The current state of technology in these areas is discussed.     

A Raman spectroscopic study of selected natural jarosites

Raman spectroscopy has been used to characterise the jarosite group of minerals of formula Mn(Fe3+)6(SO4)4(OH)12 where M may be K, (NH4)+, Na, Ag or Pb and where n = 2 for monovalent cations and 1 for the divalent cations. Raman spectroscopy proved useful for mineral identification especially where closely related minerals crystallise out from solutions where paragenetic relationships exist between the minerals. The band position of the SO4(2-) symmetric stretching mode proved to be a function of the ionic radius of the cation. The bending modes show a slight dependence. The spectra of the natural samples can be complex. This complexity is attributed to the incorporation of low levels of other cations into the structure.     

Raman spectroscopic study of the tellurite minerals: carlfriesite and spiroffite

Raman spectroscopy has been used to study the tellurite minerals spiroffite and carlfriesite, which are minerals of formula type A(2)(X(3)O(8)) where A is Ca(2+) for the mineral carlfriesite and is Zn(2+) and Mn(2+) for the mineral spiroffite. Raman bands for spiroffite observed at 721 and 743 cm(-1), and 650 cm(-1) are attributed to the nu(1) (Te(3)O(8))(2-) symmetric stretching mode and the nu(3) (Te(3)O(8))(2-) antisymmetric stretching modes, respectively. A second spiroffite mineral sample provided a Raman spectrum with bands at 727 cm(-1) assigned to the nu(1) (Te(3)O(8))(2-) symmetric stretching modes and the band at 640cm(-1) accounted for by the nu(3) (Te(3)O(8))(2-) antisymmetric stretching mode. The Raman spectrum of carlfriesite showed an intense band at 721 cm(-1). Raman bands for spiroffite, observed at (346, 394) and 466 cm(-1) are assigned to the (Te(3)O(8))(2-)nu(2) (A(1)) bending mode and nu(4) (E) bending modes. The Raman spectroscopy of the minerals carlfriesite and spiroffite are difficult because of the presence of impurities and other diagenetically related tellurite minerals.