Serpentine-group Minerals Research Articles

The Cyclops Ophiolite as a Source of High-Cr Spinels from Marine Sediments on the Jayapura Regency Coast (New Guinea, Indonesia)

The first detailed mineralogy, geochemistry and origin of heavy minerals in marine sediments along the Jayapura Regency coast on the Indonesian part of New Guinea Island are reported as part of a larger set of investigations conducted since 2009. In these sediments, the following heavy minerals were identified: high-Al and high-Cr spinels, chromian andradite, Mg-olivine, magnetite, mixture of iron (III) oxyhydroxides (limonite) and minerals from serpentine-group minerals (lizardite, antigorite). The heavy mineral fraction of marine sediments contains increased concentrations of metals, including W (up to 257.72 ppm) and Ag (up to 1330.29 ppb) as well as minor amounts of Ni (7.1–3560.9 ppm) and Cr (68.0–5816.0 ppm). The present state of geological knowledge suggests that there are no known prospects for rich Ti, Ni, Co, Cr, Au deposits along the examined part of the Jayapura coast. However, the average content of Ag and W is high enough to provide an impulse for suggested further deposit research. The source of marine sediments is Cyclops ophiolite, which contains a typical ophiolite sequence. Cyclops Mountain rocks have undergone intense chemical weathering processes and the resulting eroded material has been deposited on the narrow continental shelf. The chemical composition of chromian spinels indicates that their source is depleted peridotites from the SSZ (supra-subduction zone) environment of the Cyclops ophiolite. A detailed geochemical examination indicates that the evolution of parental melt of these rocks evolved towards magma with geochemical parameters similar to mid-ocean ridge basalt (MORB).

Gangue Entrainment in Olivine Flotation: Effect of MIBC Dosage on the Mitigation of Lizardite Recovery

Background: Olivine is an important industrial raw material especially for metallurgical applications like foundry sand, refractory, slag conditioning, etc. Loss On Ignition (LOI) value (>1%) is the main specification of olivine ore/concentrate for those areas together with the chemical specifications. Objective: This flotation study was conducted in natural pH condition with Na-oleate as collector to clarify the effect of frother (MIBC) dosage on the LOI value of olivine concentrate. Methods: Characterization of ore sample for this study was made by XRD, XRF and petrographic analyses. Lizardite, a serpentine group mineral, was found to be a hydrated soft fraction of ore sample in addition to hard olivine and pyroxene minerals constituting ore. Results: Finely ground soft lizardite adversely affected the olivine flotation in a way of entraining mechanically into concentrate. LOI value of concentrate was observed mainly to be froth volume depended issue, and therefore, mainly water recovery dependent. LOI value increased proportionally with water recovery at longer flotation time and MIBC dosages indicating the entrainment of lizardite as the suspending hydrophilic component of water phase. Certain rate of the hydrated lizardite mineral was thought to be recovered via hydrophobization, which was clearly seen especially at the initial stages of flotation period in the presence of excess frother. This experimental finding was attributed to similar chemical composition of minerals constituting ore, and accidental activation of lizardite. Conclusions: Lizardite recovery in froth was explained with accidental activation and/or weak attachment of locked particles onto froth bubble although main recovery mechanism was determined to be mechanical entrainment. Olivine concentrate obeying the specifications of metallurgical applications could be obtained at suitable MIBC dosage and flotation time.

Quantifying mass changes during hydrothermal alteration in listwaenite-type mercury mineralization, Tavreh area, northwestern Iran

The Tavreh mercury prospect, a listwaenite-type alteration/mineralization system, is located c . 90 km west of Khoy in northwestern Iran. Tavreh is hosted within the Khoy ophiolite zone. Three types of listwaenites have been recognized in the Khoy ophiolite: silica, silica-carbonate and carbonate. Of these three, Hg mineralization at Tavreh is spatially and genetically associated with the silica-type listwaenite, also known as berberite. Alteration and mineralization at Tavreh are restricted to a faulted contact between shale and serpentinite. The Tavreh listwaenite is inferred to form from the hydrothermal alteration of brecciated serpentinite. Major mineralogical changes resulting from this alteration include the decomposition of serpentine-group minerals and the formation of silica phases. In this study, the mass changes of 18 listwaenites from Tavreh were assessed relative to the least altered serpentinites. To illustrate these changes quantitatively a comparative analysis of three different methods of calculating mass change was undertaken using Grant's isocon analysis, MacLean's equation and Gresens’ equation. Results from the three methods are similar. Listwaenite alteration was associated with a large increase in SiO 2 (44.4, 36.2, 63.9%, respectively). MgO and loss on ignition were depleted (−34.8, −36.9, −36.6; −8.5, −9.3, −8.3%, respectively) and Al 2 O 3 was relatively unchanged (0.7, 0.6, 0.9%). Mercury is the most enriched rare element in altered rock (375.1, 346.8, 474.6 ppm). Arsenic, Pb, Au and Sb were also enriched. The intensity of mass changes of the various alteration components increases significantly from the serpentinite wall rock towards the listwaenite alteration and the ore-bearing zone. Therefore, the mass balance method can probably be used to locate mineral deposits from a few hundred metres and to explore for blind mineral deposits.

A Plethora of Epigenetic Minerals Reveals a Multistage Metasomatic Overprint of a Mantle Orthopyroxenite from the Udachnaya Kimberlite

More than forty mineral species of epigenetic origin have been identified in an orthopyroxenite from the Udachnaya-East kimberlite pipe, Daldyn kimberlite field, Siberian platform. Epigenetic phases occur as: (1) Mineral inclusions in the rock-forming enstatite, (2) daughter minerals within large (up to 2 mm) crystallized melt inclusions (CMI) in the rock-forming enstatite, and (3) individual grains and intergrowths in the intergranular space of the xenolith. The studied minerals include silicates (olivine, clinopyroxene, phlogopite, tetraferriphlogopite, amphibole-supergroup minerals, serpentine-group minerals, talc), oxides (several generations of ilmenite and spinel, rutile, perovskite, rare titanates of the crichtonite, magnetoplumbite and hollandite groups), carbonates (calcite, dolomite), sulfides (pentlandite, djerfisherite, pyrrhotite), sulfate (barite), phosphates (apatite and phosphate with a suggested crystal-chemical formula Na2BaMg[PO4]2), oxyhydroxide (goethite), and hydroxyhalides (kuliginite, iowaite). The examined epigenetic minerals are interpreted to have crystallized at different time spans after the formation of the host rock. The genesis of minerals is ascribed to a series of processes metasomatically superimposed onto the orthopyroxenite, i.e., deep-seated mantle metasomatism, infiltration of a kimberlite-related melt and late post-emplacement hydrothermal alterations. The reaction of orthopyroxene with the kimberlite-related melt has led to orthopyroxene dissolution and formation of the CMI, the latter being surrounded by complex reaction zones and containing zoned olivine grains with extremely high-Mg# (up to 99) cores. This report highlights the utility of minerals present in minor volume proportions in deciphering the evolution and modification of mantle fragments sampled by kimberlitic and other deep-sourced magmas. The obtained results further imply that the whole-rock geochemical analyses of mantle-derived samples should be treated with care due to possible drastic contaminations from “hiding” minor phases of epigenetic origin.

An Integrated Study of the Serpentinite-Hosted Hydrothermal System in the Pollino Massif (Southern Apennines, Italy)

A comprehensive study of the serpentinite and associated veins belonging to the Frido Unit in the Pollino Massif (southern Italy) is presented here with the aim to provide new constraints about the hydrothermal system hosted by the accretionary wedge of the southern Apennines. The studied serpentinites are from two different sites: Fosso Arcangelo and Pietrapica. In both sites, the rocks show mylonitic-cataclastic structures and pseudomorphic and patch textures and are traversing by pervasive carbonate and quartz-carbonate veins. The mineralogical assemblage of serpentinites consists of serpentine group minerals (with a predominance of lizardite), amphiboles, pyroxene, chlorite, titanite, magnetite, and talc. In some samples, hydro-garnet was also detected and documented here for the first time. As for cutting veins, different mineralogical compositions were observed in the two sites: calcite characterizes the veins from Fosso Arcangelo, whereas quartz and dolomite are the principal minerals of the Pietrapica veins infill, suggesting a different composition of mineralizing fluids. Stable isotopes of C and O also indicate such a different chemistry. In detail, samples from the Pietrapica site are characterized by δ13C fluctuations coupled with a δ18O shift documenting calcite formation in an open-system where mixing between deep and shallow fluids occurred. Conversely, δ13C and δ18O of the Fosso Arcangelo veins show a decarbonation trend, suggesting their developing in a closed-system at deeper crustal conditions. Precipitation temperature calculated for both sites indicates a similar range (80 °C to 120 °C), thus suggesting carbonate precipitation within the same thermal system.

Mineralogical Characterization of Dolomitic Aggregate Concrete: The Camarasa Dam (Catalonia, Spain)

The Camarasa Dam was built in 1920 using dolomitic aggregate and Portland cement with two different compositions: type A (dolomite and Portland cement) and type B (dolomite and sand-cement). The sand cement was a finely powdered mixture of dolomite particles and clinker of Portland cement. The mineralogy of concrete was studied by optical microscopy, scanning electron microscopy, and x-ray powder diffraction. Reaction of dedolomitization occurred in the two types of concrete of the Camarasa Dam, as demonstrated by the occurrence of calcite, brucite, and/or absence of portlandite. In the type A concrete, calcite, brucite, and a serpentine-group mineral precipitated as a rim around the dolomite grains and in the paste. The rims, a product of the dedolomitization reaction, protected the surface of dolomite from the dissolution process. In type B concrete, in addition to dolomite and calcite, quartz and K-feldspar were present. Brucite occurred in lower amounts than in the type A concrete as fibrous crystals randomly distributed in the sand-cement paste. Although brucite content was higher in the type A concrete, type B showed more signs of loss of durability. This can be attributed to the further development of the alkali-silica reaction in this concrete type.

A synthesis and meta-analysis of the Fe chemistry of serpentinites and serpentine minerals.

The iron chemistry of serpentinites and serpentine group minerals is often invoked as a record of the setting and conditions of serpentinization because Fe behaviour is influenced by reaction conditions. Iron can be partitioned into a variety of secondary mineral phases and undergo variable extents of oxidation and/or reduction during serpentinization. This behaviour influences geophysical, geochemical and biological aspects of serpentinizing systems and, more broadly, earth systems. Iron chemistry of serpentinites and serpentines is frequently analysed and reported for single systems. Interpretations of the controls on, and the implications of, Fe behaviour drawn from a single system are often widely extrapolated. There is a wealth of serpentinite/serpentine chemical composition data available in the literature. Consequently, compilation of a database including potential predictors of Fe behaviour and measures of Fe chemistry enables systematic investigation of trends in Fe behaviour across a variety of systems and conditions. The database presented here contains approximately 2000 individual data points including both bulk rock and serpentine mineral geochemical data which are paired whenever possible. Measures of total Fe and Fe oxidation state, which are more limited, are compiled with characteristics of the systems from which they were sampled. Observations of trends in Fe chemistry in serpentinites and serpentines across the variety of geologic systems and parameters will aid in verifying and strengthening interpretations made on the basis of Fe chemistry. This article is part of a discussion meeting issue 'Serpentinite in the Earth system'.

Arsenic-Bearing Serpentine-Group Minerals: Mineral Synthesis with Insights for the Arsenic Cycle

AbstractWhen present at elevated levels in drinking water, arsenic is toxic, and magnesian clays are gaining recognition as a source of elevated arsenic in groundwater. In the crust and upper mantle of Earth, arsenic incorporation into clay minerals is influenced by geochemical conditions associated with hydrothermal fluids and metamorphic processes (e.g. serpentinization), meaning that As is a useful tracer of fluid-flow in the deep Earth. To improve understanding of arsenic speciation in groundwater, sediments, soils, and hydrothermal-metamorphic systems, the present study examined arsenic incorporation into magnesian clays by synthesis of serpentine minerals (200oC, 10 d) with varied concentrations of Si, Al, As5+, and As3+. The synthesis experiments produced two distinct crystal types, tubular and platy serpentines, each with 10–15% randomly interstratified talc layers. X-ray absorption spectroscopy indicated that As5+ and As3+ occurred in the tetrahedral sheet. Single-crystal analysis revealed that tubular crystals contained up to 1 wt.% arsenic [Mg2.8(Si1.8As0.2)O5(OH)4] (mean 0.2 wt.% As). The mean composition of platy, high-Al crystals is (Mg1.8Al0.7)(Si2.0)O5(OH)4, and that of platy, medium-Al crystals with As3+ is (Mg2.07Al0.52) (Si1.97As3+0.03)O5(OH)4. Charge, geometry, and radius of tetrahedral AsO43– oxyanions are similar to tetrahedral SiO44–, and this facilitates fixation of As5+ into the tetrahedral sheet of clay minerals. The geometry and size of the larger As3+ in tetrahedral sites (as a pyramidal AsO33– oxyanion) may limit incorporation relative to As5+. Arsenic-bearing Mg clays crystallize in alkaline environments where AsO43– or AsO33– are the dominant As species and where high pH accompanies crystallization of serpentine, talc, chlorite, or Mg-smectite. The presence of tetrahedral As in these clays raises the possibility of tetrahedral As in other Mg clays (e.g. sepiolite or kerolite) as well.

Raman characteristics of Alpine–Himalayan serpentine polymorphs: A case study of Khankuie ultramafic complex, southeast of Iran

Chrysotile, antigorite, and lizardite were analyzed to determine their chemical and structural properties as a function of Raman spectral patterns. Serpentine polymorph discrimination is a challenging issue as each polymorph represents different crystal structure and different thermodynamic phase situation of formation. Microtextural investigation, SEM (Scanning Electron Microscope), XRD (X-Ray Diffraction), and EMPA (Electron Microprobe Analysis) illustrate that there are some chemical and structural variations between our studied serpentine polymorphs. In the case of the three strongest Raman peaks at around 230, 390 and 690 cm−1, we obtained that antigorite tends to lower Raman Stoke lines, lizardite to moderate wavenumbers and the highest Raman Stoke lines belong to chrysotile. These main bands with principal peaks were used to find special spectral peak patterns of each polymorph, along with some other ‘weak’ peaks (around 350, 520, and 620 cm−1) with different behaviours. When Raman Stoke line shifts were plotted against each other, we reached to 25 scatter plots with different classified validation. The best 2d scatter discrimination diagrams are those of 230–390 cm−1 and 350–390 cm−1 with the overall accuracy rate of 94% and 98%, respectively. Also, there are proportional relations between chemical band vibrations of SiO4, MgO, and H2O, and Raman Stoke lines of 390, 620 and 230 cm−1, respectively. This information increases our ability to predict polymorph types and geochemical trends of serpentine group minerals just using the Raman spectra.

Serpentine Tribotechnical Composition «Saranovsky». Preparation and Comparative Tests

Non-traditional tribotechnics with the use of organic, metal and mineral tributechnical compositions allows for without disassembly repair of worn-out friction units of various civil and military equipment. From 1942 it developed a slow but with 2000 there were over 200 different tribological compounds, of which in Europe, Asia, America wide-ly used a few dozen. In Russia, due to the simplicity of preparation, application and efficiency, the most widely used powders of minerals of the serpentine group were found. Their creation and justification of application took place in the 80-90s years in St. Petersburg and many other research institutes of Russia. Tribological studies of highly dispersed powders of the serpentine group minerals – magnesium hydrosilicates Mg6[Si4O10](OH)8 and similar, as well as performance testing of their application was carried out in the Nanocentre of research Institute GOSNITI. Here in the research serpentine compositions or geomodificators friction conducted more than 5,000 tests 80 different songs, and in the center UNIITiN conducted operational testing tribotechnical composition, created Nanocenter GOSNITI. In creating the serpentine tribotechnical composition in the Nanocenter GOSNITI waste is used flotation chrome ore Deposit mining facility. Powders were purified, subje-cted to heat treatment, mechanoactivation on a planetary ball mill ACTIVATOR 2SL, be-fore and after preparation was investigated on X-Ray diffractometer XRD 6000, and on an inverted metallographic microscope OLUMPUS GX 51. Laboratory tribotechnical tests of the finger-disc steel pair in engine oil with tribo-compositions were carried out on the TRB-S-DE tribometer in the step loading mode to a pressure of 218 MPa at a sliding speed of 100 cm/s. These comparative tests showed that the tribo-composition of Saranovsky in mineral motor oil of quality classes SS API and viscosity 30 SAE (manufacturer Russia) approximated its tribological properties to the best in the world motor oil firm Mobil to the coefficient of friction 0.04. 250-hour performance testing in the center UNIITiN in three diesel engines of Rus-sian tractors showed a decline in fuel consumption by 5-8 %, of oil burning on 10-12 %, the opacity of gases by 8-15 %, and iron content in oils by 20-25 %. This once again confirmed the known from the late 80-s years of the effectiveness of in-place repair of serpentine structures to increase their service life automotive engineering. Summarizes the features of the building and tribological properties of serpentine coatings. From this it is assumed that the growth of the carbon-containing coating, even with the removal of the tribotechnical composition from the oil, is due to the activation of friction coatings and the unique properties of the atoms of the carbon, the possibilities of sp2, sp3 hybridization, chemisorption coatings of hydrocarbon lubricants, and in the interfaces to dry and also carbon dioxide environment.

Assessment of Serpentine Group Minerals in Soils: A Case Study from the Village of San Severino Lucano (Basilicata, Southern Italy)

Naturally occurring asbestos (NOA) is a generic term used to refer to both regulated and un-regulated fibrous minerals when encountered in natural geological deposits. These minerals represent a cause of health hazard, since they have been assessed as potential environmental pollutants that may occur both in rocks and derived soils. In the present work, we focused on the village of San Severino Lucano, located in the Basilicata region (southern Apennines); due to its geographic isolation from other main sources of asbestos, it represents an excellent example of hazardous and not occupational exposure of population. From the village and its surroundings, we collected eight serpentinite-derived soil samples and carried out Differential Scanning Calorimetry (DSC), Derivative Thermogravimetric (DTG) and Transmission Electron Microscopy with Energy Dispersive Spectrometry (TEM-EDS), in order to perform a detailed characterization of serpentine varieties and other fibrous minerals. Investigation pointed out that chrysotile and asbestos tremolite occur in all of the samples. As for the fibrous but non-asbestos classified minerals, polygonal serpentine and fibrous antigorite were detected in a few samples. Results showed that the cultivation of soils developed upon serpentinite bedrocks were rich in harmful minerals, which if dispersed in the air can be a source of environmental pollution.

Naturally Occurring Asbestos (NOA) in Granitoid Rocks, A Case Study from Sardinia (Italy)

All six minerals defined as “asbestos” by the existing regulation on asbestos hazard, i.e., actinolite, tremolite, anthophyllite, crocidolite and amosite amphiboles, and the serpentine-group mineral chrysotile are typical constituents of mafic and ultramafic magmatic rocks of ophiolitic sequences. However, little is known about the presence and distribution of naturally occurring asbestos (NOA) in plutonic felsic rocks. The Isadalu magmatic complex outcropping in central Sardinia and belonging to the post-variscan Permian volcanic cycle, is described here as an interesting occurrence of fibrous amphiboles in granitoid rocks. Field work and collected mineralogical/petrological data show that NOA fibers from the Isadalu complex belong compositionally to the actinolite-tremolite series. They were generated by metasomatic growth on pristine magmatic hornblende, at ca. 470 °C at 1 kbar, during sodic-calcic hydrothermal alteration. In terms of environmental hazard, the Isadalu complex represents a high-value case study, since the actinolite-bearing felsic rocks outcrop in a strongly anthropized area. Here, towns with local and regional strategic infrastructures (dams, pipes, hydroelectric power plants, water supply, roads) have been developed since the last century, also using the granitoid asbestos-rich stones. The aim of this study is to demonstrate that NOA and relative hazard are not univocally connected to a restricted typology of rocks. This result should be taken into account in any future work, procedure or regulation defining asbestos occurrences in natural environments.

Modeling and assessment of wavelength displacements of characteristic absorption features of common rock forming minerals encrusted by lichens

Arctic environments provide a challenging ground for geological mapping and mineral exploration. Inaccessibility complicates ground surveys and the presence of ice, vegetation, and lichens hinders supportive remote sensing surveys. Spectral mixing of lichens and bare rock can shift the wavelength position of characteristic absorption features, thereby complicating the spectral mapping of minerals and lithologies. The extent to which diagnostic rock features are preserved despite the presence of lichens is of major concern in remotely sensed geological studies and estimates of the critical level of lichen coverage, below which spectral features of the mineral substrate can still be identified, are needed. We investigated how surficial lichen cover affects the characteristics of shortwave infrared (SWIR) mineral absorption features and the efficacy of automated absorption feature extraction. For this purpose, mixed spectra were synthetically generated from laboratory spectra of common rock forming SWIR absorbing minerals and lichens. Wavelength displacements of characteristic absorption features for each mixed spectrum were then analyzed as a function of percentage lichen cover. Distinctive trends were identified that can be used in future analysis: The strong spectral features of mica group minerals around 2200 and 2340–2350nm maintain their integrity for up to 30% lichen cover, despite the related shift toward shorter wavelengths for higher percentage lichen cover. In contrast, very weak absorption bands around 2440nm in (white) micas spectra are completely obscured for a lichen cover of ≥50%. Our observations suggest that the chlorite feature around 2250nm is shifted toward longer wavelengths and the depth of this feature as well as the contrast between lichen and substrate spectra define the amount of lichen needed to mask it. Furthermore, lichens induce a spectral shift towards shorter wavelengths for the features around 2320nm for the rocks containing amphibole, chlorite, carbonate and serpentine group minerals. In addition, no wavelength displacement is observed for chlorite, biotite and phlogopite features around 2380nm in mixtures with lichens. By quantifying lichen cover effects on mineral absorption features, our study highlights the importance of being precautious in any interpretation in areas characterized by abundant lichen-covered outcrops. This can be of significant importance for mineral and deposit vectoring as the presence of abundant lichen coverage causing slightly shifted features for a given spectra can be erroneously identified as a path to a deposit.

Evolution of borate minerals from contact metamorphic to hydrothermal stages: Ludwigite-group minerals and szaibélyite from the Vysoká – Zlatno skarn, Slovakia

Borate minerals of the ludwigite group (LGM) and szaibelyite in association with hydroxylclinohumite, clinochlore, a serpentine mineral, magnesian magnetite, spinel, magnesite, dolomite and sulphide minerals, occur in a magnesian exoskarn in the R-20 borehole located in the Vysoka – Zlatno Cu-Au porphyry-skarn deposit, located within the Stiavnica Neogene stratovolcano, Western Carpathians, central Slovakia. The skarn is developed along the contact of Miocene granodiorite to quartz-diorite porphyry and a Middle-Upper Triassic dolomite-shale-psammite-anhydrite sedimentary sequence. The boron minerals were investigated by electron probe micro-analyser (EPMA) and micro-Raman techniques. The source of boron could have been from the granodiorite/quartz diorite intrusion; however some supply of B from adjacent evaporite-bearing sediments is also possible. Based on textural and compositional data, the minerals originated during two stages. (1) An early high-temperature, contact-metamorphic and metasomatic stage comprises coarse-crystalline aggregate of LGM (types 1 to 3) in association with hydroxylclinohumite, magnetite, and rarely spinel inclusions in LGM. Compositional variations of LGM show a crystallization sequence from early azoproite [≤17 wt% TiO2; ~0.40 atoms pre formula unit (apfu) Ti, which correspond to ≤79 mol% of the Mg2(Mg0.5Ti0.5)O2(BO3) end-member], Ti-Al-rich members of LGM, “aluminoludwigite “[≤14 wt% Al2O3; ≤0.53 apfu, ≤53 mol% of Mg2AlO2(BO3) end-member] and Al-rich ludwigite in the central zone of crystals, to Ti-Al-poor ludwigite in outer parts of crystals. (2) Minerals of the late retrograde serpentinization and hydrothermal stage form irregular veinlets and aggregates, including partial alteration of hydroxylclinohumite to the serpentine-group mineral and clinochlore, replacement of LGM by szaibelyite, formation of the latest generation of Fe-rich, Ti-Al poor ludwigite in veinlets (type 4), and precipitation of dolomite, magnesite and sulphide minerals (valleriite, sphalerite, chalcopyrite). The distinct compositional zoning of the LGM documents a complex evolution of the skarn beginning with a high-temperature stage 1 and ending with a low-temperature overprint, stage 2.

Ludwigite-group minerals and szaibelyite - rare borate minerals from Vysoká – Zlatno skarn, Štiavnica stratovolcano, Slovakia [abstract

Beside of sedimentary evaporitic rocks, borate minerals occur also in some high temperature contact-metamorphic rocks, especially in skarns, locally in association with Fe and Sn ore minerals (e.g., Anovitz and Grew, 1996). The borate minerals are generally associated to the post-magmatic processes which occur in the contact aureolas of intrusive, acid to intermediary, calc-alkaline rocks (Pertsev, 1991). Borate minerals of the ludwigite group and szaibelyite were identificated from the Mg-skarn in the R-20 drilling core during geological exploration for Cu-Au porphyry-skarn ores in the Vysoka – Zlatno area near Banska Stiavnica, in the Stiavnica Neogene stratovolcano, centralSlovakia(Koděra et al., 2010). Ludwigite-group minerals (LGM) form massive black aggregates (>5 cmlarge) of numerous acicular, euhedral to subhedral prismatic crystals (usually 0.2 to 3 mmlong). Ludwigite associates with clinohumite, szaibelyite, clinochlore, serpentine-group mineral, magnesite, dolomite, hematite, rarely valeriite, chalcopyrite, and sphalerite. Under transmitted light, LGM crystals are mostly opaque; locally they are translucent with strong pleochroism in sections parallel to z-axis (deep green - dark reddish brown). In BSE, LGM crystals show regular concentric, rarely oscillatory or irregular zoning caused by distinct element variations during their growth or partial alteration: the dark zones show enrichment in Mg, Al and Ti, in contrast to the pale zones which reveal larger amounts of Fe. The electron-microprobe analyses reveal growth evolution of LGM crystals from Al-rich azoproite [with £79 mol.% of Mg 2 (Mg 0.5 Ti 0.5 )(BO 3 )O 2 end-member] to Al±Ti-rich ludwigite and Al-dominant LGM phase [“aluminoludwigite” with £53 mol.% of Mg 2 Al(BO 3 )O 2 end-member] in central zones, whereas rim zones of the crystals and secondary veinlets attain nearly pure ludwigite composition [87–99 mol.% of Mg 2 Fe 3+ (BO 3 )O 2 end-member]. Consequently, LGM from the Vysoka – Zlatno skarn show the largest compositional variations ever known from one occurrence and they reach the highest contents of Ti (£17.4 wt.% TiO 2 , 0.39 apfu) and Al (£14.4 wt.% Al 2 O 3 ,0.53 apfu) ever reported in LGM (Schaller and Vlisidis, 1961; Marincea, 2000; Pertsev et al., 2004; Aleksandrov and Troneva, 2008, 2011). The compositional variations indicate the following substitution mechanisms in the studied LGM: Mg 2+ = Fe 2+ for the all compositions, Fe 3+ = Al 3+ for samples without higher amount of Ti, and 2Al = Mg 2+ +Ti 4+ or 2Fe 3+ = Mg 2+ +Ti 4+ for analyses including high Ti content. Szaibelyite MgBO 2 (OH) occurs as aggregates of fibrous crystals, up to 0.5 mm in size, replacing LGM. Zoning in szaibelyite was not observed. The amounts of Mg are uniform (0.98 to 0.99 apfu), content of Fe 2+ oscillates from 0.2 to 1.2 wt.% FeO (0.002–0.014 apfu) and indicates the Mg 2+ = Fe 2+ substitution. Szaibelyite also contains small admixtures of Mn (0.1–0.4 wt.% MnO), Al and Cr (£0.3 wt.% Al 2 O 3 or Cr 2 O 3 ). The skarn mineralization originated as a result of contact thermal metamorphism of Miocene calc-alkaline granodiorite intrusion on host Middle to Upper Triassic limestones, dolomites, shales and evaporitic anhydrite beds (the Veľký Bok Group). The evaporites were most likely the primary source of boron, whereas Ti was probably derived from the granodiorite. Clinohumite and LGM (azoproite to Al±Ti-rich ludwigite and “aluminoludwigite”) precipitated during the high-temperature contact metamorphic event at ~700 °C and £100 MPa, whereas the youngest Al,Ti-poor ludwigite veinlets, szaibellyite, serpentine-group mineral, clinochlore, magnesite, dolomite, hematite and probably also sulfide minerals were formed during younger, lower-temperature hydrothermal-metasomatic event.

Micro‐Raman mapping of the polymorphs of serpentine

Serpentinites are rocks, often used in buildings, formed in large extent by minerals of the serpentine group: chrysotile, antigorite, lizardite, and polygonal serpentine. The fibrous type (e.g. chrysotile) of serpentine group minerals, along with several amphibole varieties (e.g. actinolite and tremolite), are the major components of asbestos family. The exposure to fine fibrous asbestos powder is linked to diseases such as pleural mesothelioma and asbestosis. The identification of the main varieties of the serpentine group, laminated or fibrous, becomes an issue of great interest for public health. This work introduces an analytical strategy able to distinguish the different serpentine polymorphs directly on the sample, allowing the analysis within their textural environment, evidencing at the micrometer scale the mineral reactions of the phases. Samples coming from the Koniambo massif (Grande Terre Island, New Caledonia) were studied by means of optical microscopy, scanning electron microscopy–energy dispersive X‐ray spectroscopy, and Raman spectroscopy. Raman peaks observed in the high wavenumber spectral range of 3550–3850 cm−1, associated with OH stretching vibrations, allow the discrimination of the all four serpentine varieties. The relationship between the different varieties of serpentine, at a micrometric scale, in complex samples, has been investigated by two‐dimensional Raman mapping. Copyright © 2015 John Wiley & Sons, Ltd.

Stoichiometric Reactions Describing Serpentinization of Anhydrous Primary Silicates: A Critical Appraisal, with Application to Aqueous Alteration of Chondrule Silicates in CM Carbonaceous Chondrites

AbstractA number of chemical reactions (mass-action expressions) have been proposed to describe serpentinization of olivine in terrestrial serpentinites. Some have been applied to interpreting the formation of serpentine-group minerals in CM carbonaceous chondrites. The widely used olivine + pyroxene → serpentine (ol + px → srp) reaction is quantitatively inconsistent with observed ratios of olivine to pyroxene and olivine to serpentine in CM carbonaceous chondrites. The reaction of 5ol → 2srp is most consistent with constraints from textural observations at the scale of individual partial and complete pseudomorphs of serpentine after coarse olivine in CM chondrites, observed co-variations in modal abundances of reactant and product minerals in CM chondrites, and experimental geochemical kinetics. Furthermore, the 5ol → 2srp reaction provides insight into the mobility of solute species in the aqueous alteration environment of CM carbonaceous chondrites.

Weakly shocked and deformed CM microxenoliths in the Pułtusk H chondrite

AbstractThe Pułtusk meteorite is a brecciated H4–5 chondrite cut by darkened cataclastic zones. Within the breccia, relict type IA, IB, and IIA chondrules, and microxenoliths of carbonaceous CM chondrite lithology occur. This is the first description of foreign clasts in the Pułtusk meteorite. The matrix of the xenoliths was identified by usage of microprobe and Raman spectroscopic analyses. Raman spectra show distinct bands related to the presence of slightly ordered carbonaceous matter at approximately 1320 and 1580–1584 cm−1. Bands related to serpentine group minerals are also visible, especially a peak at 692 cm−1 and moreover other weak bands are interpreted as evidence for tochilinite. We decipher the metamorphic and deformational history of the xenoliths. They experienced aqueous alteration before being incorporated into the unaltered and well‐equilibrated parent rock of the Pułtusk chondrite. The xenoliths are weakly shocked as indicated by defects in the crystal structure of silicates and carbonates, but hydrated minerals (serpentine and tochilinite) are still present in the matrix. The carbonaceous matter within the clasts' matrix displays first order D and G Raman bands that suggests it is only slightly ordered as a result of mild thermal processing. Distinct shear bands are present in both the xenoliths and the surrounding rock, which testifies that the xenoliths were affected by a deformational event along with host rock. The host rock was brittly deformed, but the clasts experienced more ductile deformation revealed by semibrittle faulting of minerals, kinking of the tochilinite‐cronstedtite matrix, and injections of xenolithic material into the adjacent breccia. We argue that both processes, the high strain‐rate shear deformation and the incorporation of the xenoliths into the host Pułtusk breccia, could have been impact‐related. The Pułtusk xenoliths are, thus, rather spalled collisional fragments, than trapped fossil micrometeorites.

Serpentinites: Essential Roles in Geodynamics, Arc Volcanism, Sustainable Development, and the Origin of Life

Serpentinites are rocks consisting mostly of the serpentine-group minerals chrysotile, lizardite and antigorite. They are formed by the hydration of olivine-rich ultramafic rocks and they contain up to ~13 wt% H 2 O. They have long been used by many cultures as building and carving stones. Serp entinites play essential roles in numerous geological settings. They act as a lubricant along plate boundaries during aseismic creep and contribute to the geochemical cycle of subduction zones. In the mantle, they are a reservoir of water and fluid-mobile elements. Serpentinites can produce nickel ore where weathered, and they can sequester CO 2 where carbonated. They may have provided an environment for the abiotic generation of amino acids on the early Earth and other planets, potentially leading to the development of life.

Rheology and Tectonic Significance of Serpentinite

Serpentinites occur in many active geologic settings and control the rheology of the lithosphere where aqueous fluids interact with ultramafic rocks. The crystal structure of serpentine-group minerals results in diagnostic physical properties that are important for interpreting a wide range of geophysical data and impart unique rheological behaviors. Serpentinites play an important role during continental rifting and oceanic spreading, in strain localization along lithospheric strike-slip faults, and in subduction zone processes. The rheology of serpentine is key for understanding the nucleation and propagation of earthquakes, and the relative weakness of serpentinite can significantly affect geodynamic processes at tectonic plate boundaries.