Siliceous Stone Research Articles

Critical Raw Materials Supply: Challenges and Potentialities to Exploit Rare Earth Elements from Siliceous Stones and Extractive Waste

Critical raw materials (CRMs) supply is a challenge that EU countries have to face, with many thinking about domestic procurement from natural ore deposits and anthropogenic deposits (landfills and extractive waste facilities). The present research focuses on the possibilities linked to the supply of CRMs and the potential for exploiting rare earth elements (REEs), investigating a large variety of extractive waste and siliceous rocks in the Piedmont region (Northern Italy). Indeed, the recovery of REEs from the extractive waste (EW) of siliceous quarries and other siliceous ore deposits can be a valuable way to reduce supply chain risks. Starting with a review of the literature on mining activities in Piedmont and continuing with the sampling and geochemical, mineralogical, petrographic, and environmental characterization of EW facilities connected to siliceous dimension stones, of kaolinitic gneiss ore deposits, and of soils present near the investigated areas, this study shows that the degree of REEs enrichment differs depending on the sampling area (soil or EW) and lithology. The concentration of REEs in the EW at some sampling sites fulfils the indicators of industrial-grade and industrial recovery; the high cumulative production and potential market values of EW and the positive recovery effects through proven methodologies indicate a viable prospect of REE recovery from EW. However, REE recovery industrialization faces challenges such as the difficulty in achieving efficient large-scale recovery due to large regional differences in REE abundance, the mismatch between potential market value and waste annual production, etc. Nonetheless, in the future, EW from dimension stone quarries could be differentially studied and reused based on the enrichment and distribution characteristics of trace elements. The present paper shows investigation procedures undertaken to determine both CRMs potentialities and environmental issues (on the basis of literature data employed to select the more-promising areas and on sampling and characterization activities in the selected areas), together with procedures to determine the waste quantities and tentative economic values of REEs present in the investigated areas. This approach, tested on a large area (Piedmont region), is replicable and applicable to other similar case studies (at EU and non-EU levels) and offers decision makers the possibility to acquire a general overview of the potential available resources in order to decide whether and where to concentrate efforts (including economic ones) in a more detailed study to evaluate the exploitable anthropogenic deposits.

Bio-Modifier: A Sustainable Suturing Technology at the Bitumen–Aggregate Interface

Premature failure at the bitumen–aggregate interface is attributed to the surface chemistry of stone aggregates. Bitumen modifiers with high affinity toward aggregates are often used to change the surface chemistry of aggregates, which in turn changes the type and strength of stones’ interactions with bitumen. Here, the mechanisms of action and the effects of an organosilane and bio-oil separately on the bitumen–aggregate interface, including their binding to aggregates from one side and to bitumen from the other side, were studied and compared. The binding of bio-oils and organosilanes to aggregates is well documented, as well as their efficacy as anti-stripping agents, but their binding to bitumen is not well understood. Using glass beads as a surrogate for siliceous stones, we obtained laboratory measurements of interfacial strength as measured by resistance to shear forces at the interface of bitumen and silica. Our laboratory measurements showed the highest value for the bitumen modified with bio-oil, followed by the control bitumen with no modification, and the lowest value for the bitumen modified with organosilane. Our molecular modeling calculations showed that the adhesion of bitumen molecules to silica coated with bio-oil was notably stronger (up to 72%) than the adhesion of bitumen molecules to silica coated with organosilane. The higher interfacial strength observed for bitumen with bio-oil is attributed to bio-oil having various functional groups with the ability to form hydrogen bonds and π–π interactions with the aromatic and polar components of bitumen. The study outcomes highlight the importance of modifiers’ ability to strongly interact with both aggregates and bitumen. The bio-oil modifier introduced in this work can form a robust bridge between bitumen and siliceous aggregates to improve the adhesive properties, enhancing the sustainability and durability of bituminous composites.

Self-compacting concrete between workability performance and engineering properties using natural stone wastes

The current work aims at studying the chemical and mineralogical composition in addition to the physical properties of natural stone wastes as cement replacement and their effect on the fresh and hardened properties of self-compacting concretes (SCC). In the present study, two types of natural stone wastes were used: carbonaceous stone wastes (C) and siliceous stone wastes (S). The chemical, mineralogical, and physical characterization of the different wastes were performed using X-ray fluorescence (XRF), X-ray diffraction (XRD), water pycnometer, and Specific surface area.Nine SCC mixes coded (Ref., C10, 20, 30, 40% - S10, 20, 30, 40%) were formulated by incorporating four proportions of each type of the stone wastes other than the reference mix. The initial and final setting times, fresh density, air content, flowing - ability by slump flow, filling ability by T500 and V-funnel time, passing ability by L-box, U-box, and block assessment by J-ring were measured for the fresh mixes. For the hardened mixes, the water absorption, density, voids, compressive, flexure, and splitting tensile strengths were tested, in addition to their resistances against water penetration and chloride ion penetration, as well as sulfuric acid attack.The results revealed a slight to noticeable enhancement in the workability performance of SCCs with increasing stone wastes proportions. Using up to 40% stone wastes led to an increase in the flow- and passing-abilities by not less than (1.45%, 4.88%), while decreasing in the filling times by not less than (7.14%, 30%) as compared to the reference mix with a slight sign of bleeding and lacking an evidence of segregation or blocking.Using up to 10% stone wastes has an insignificant drop in the water absorption and density, compressive, flexure, and splitting tensile strengths values by not more than (1.64%, 0.42%, 3.65%, 3.88%, 10.51%), respectively at late age. A better resistance toward the sulphuric acid attack, in terms of strength and mass loss, was noticed for all replacement levels by not less than (17%, 13%), respectively at maximum exposure time, as compared to the reference mix.

Rubidium measured by XRF as a predictor of soil particle size in limestone and siliceous parent materials

PurposeInformation about particle size distribution (PSD) and soil texture is essential for understanding soil drainage, porosity, nutrient availability, and trafficability. The sieve-pipette/gravimetric method traditionally used for particle size analysis is labour-intensive and resource-intensive. X-ray fluorescence (XRF) spectrometry may provide a rapid alternative. The study’s aim was to examine the use of XRF for rapid determination of PSD in Irish soils.MethodsSoils (n = 355) from existing archives in Ireland were analysed with a benchtop energy-dispersive XRF (EDXRF). Correlation and regression analyses were determined to compare Rb, Fe, Al, and Si concentrations to % clay, % silt, and % sand. Also, linear regression models were developed to compare % clay, % sand, and % silt measured by the gravimetric method to values predicted by EDXRF.ResultsThe relationship between element concentration and PSD was dependent on parent material. Rb, Al, and Fe showed a significant (p < 0.05) correlation (r > 0.50) with % clay and % sand in soils derived from limestone and siliceous stone parent materials. Rb was the best predictor for % clay (R2 = 0.49, RMSE = 10.20) in soils derived from limestone and siliceous stone-derived soils.ConclusionGeochemistry and clay mineralogy of the soils’ parent material strongly influenced the EDXRF’s ability to predict particle size. The EDXRF could predict % clay in soils from parent materials which weather easily, but the opposite was true for soils with parent material recalcitrant to weathering. In conclusion, this study has shown that the EDXRF can screen % clay in soils derived from limestone and siliceous stone parent materials.

Protein enriched biowaste: A viable feedstock to make durable bio-binders for bituminous composites

Low resistant to water damage is a major concern in bituminous composites used in roads and roofs. Water damage is attributed to desorption of molecules which are pre-adsorbed to siliceous stone mainly due to the water molecules' higher affinity to active sites of siliceous substrates. This paper shows feasibility of engineering highly water-resistant bio-modifiers from a hybrid biomass feedstock containing a balanced combination of protein and lipid. In the present study, this concept is illustrated by synthesizing a novel bio-modifier referred to as Swilgae from coliquefaction of high-protein algae (A) with high-lipid swine manure (S) for use in bituminous composites. To examine efficacy of Swilgae bio-modifier to enhance bitumen's resistance to water damage, this paper specifically studies adsorption and de-wetting of Swilgae molecules from siliceous substrates as surrogates for quartz and granite stones used in bituminous composites. To do so, we use computational modeling geared toward the use of density functional theory (DFT) combined with laboratory experiments using a moisture-induced shear-thinning test and in-situ Fourier transform infrared (FTIR) spectroscopy. The study results showed that Swilgae bio-modifier is more effective at improving the asphalt resistance to moisture damage than those made from either algae or manure individually, owing to the synergy between lipid-rich swine manure combined with protein-rich algae. This was evidenced in bitumen containing 1A:1S Swilgae showing the least change in the moisture-induced shear thinning among all studied scenarios. This was attributed to the molecular structures of the Swilgae having both lower polarizability and higher adsorption energy per unit area of siliceous surface compared to those made from isolated feedstock. Additionally, Swilgae showed to passivate the active sites of silica and replace water molecules over the silica surface via a competitive adsorption with the water molecules on the hydroxylated silica surface that is consistent with the FTIR results. Therefore, 1A:1S Swilgae molecules build a well-structured bridge between bitumen and siliceous substrates, leading to improved adhesive forces and subsequently enhaced durability in the bituminous composites used in roads and roofs.

The effect of progressive aging on the bond strength of bitumen to siliceous stones

Oxidative aging changes the composition of bitumen, and these changes affect the cohesive properties and adhesive properties of the bitumen. While cohesive properties of bitumen have been shown to be negatively impacted by aging, bitumen's bonding strength to stone aggregates can increase. Aging makes bitumen become more polar and gives rise to concentration of oxidized asphaltenes. It is hypothesized that oxidized asphaltenes show stronger interaction with siliceous substrates, promoting bitumen's bonding to siliceous stones such as quartz and granite. This study uses computational modeling and laboratory experiments to evaluate the interaction of progressively aged bitumen with siliceous substrates. To do so, asphalt samples aged from 20 to 60 hours were prepared, and their bonding properties were examined in dry conditions and wet conditions. The study results showed that as bitumen becomes aged and/or exposed to water, its shear thinning increases. Our computational modeling showed oxidation promotes the interaction between bitumen components and silica. In terms of bitumen’s bonding to stones, our modeling results showed that oxidized compounds of bitumen such as asphaltene and resin have higher interaction energies with siliceous surfaces than non-oxidized counterpatrs. Our experiments found that siliceous stones (represented by glass beads in experiment) had greater interaction with aged bitumen than with unaged bitumen. Furthermore, aged bitumen showed even higher interaction with siliceous stones when exposed to water compared to dry conditions, as shown by the moisture-induced shear-thinning index (MISTI) test. The latter observations indicate that water could not diffuse into the interface of aged bitumen and siliceous stones to weaken their bond. The outcomes of the study provide insights pertaining to bitumen’s adhering to stones. It further informs methods related to the extraction of bituminous compounds from reservoir rocks as well as removal of oxidized bitumen from stones when reclaiming old asphalt pavements.

Environmental and mechanical impacts of waste incinerated acidic sludge ash as filler in hot mix asphalt

In this paper, the feasibility of employing waste incinerated acidic sludge ash (IASA) as a viable alternative to the mineral fillers in hot mix asphalt (HMA) with a siliceous aggregate source from environmental and mechanical aspects was investigated. Environmental impacts were analyzed considering four factors: ignitability, reactivity, corrosivity using pH test, and toxicity using toxicity characteristic leaching procedure test. Mechanical properties of mixtures were obtained using indirect tensile strength (ITS), resilient modulus, moisture sensitivity, and permanent deformation tests. Results revealed that all metal concentrations leached from IASA modified HMA and pH of IASA modified samples comply with the United States Environmental Protection Agency (EPA). It was also demonstrated that incorporation of IASA in HMA leads to enhancement of HMA mechanical properties. ITS and resilient modulus of mixtures containing IASA were higher than those of the control mixtures. Replacing 50 wt.% of siliceous stone dust filler with IASA causes an increment about twofold in the flow number and reduction of the rut depth by about 26 % compared to those of the control sample. Moreover, the hydrophobicity and impermeability properties of IASA modified HMA and the stronger interfacial reaction between asphalt and IASA, resulted in improving the moisture susceptibility of the mixture containing IASA. This paper provides more insights on IASA waste management through its application in an environmentally friendly HMA.

Transesterification of Waste Cooking Oil to Produce A Sustainable Rejuvenator for Aged Asphalt

This study examines the merits of esterification of waste cooking oil to reduce its acidic content for use as a rejuvenator for aged asphalt. It further examines how acidic compounds in bitumen increases the moisture susceptibility of bituminous composites made from siliceous stones and bitumen. While some acidic compounds are inherent in bitumen, the recent widespread use of bio-modifiers such as waste cooking (vegetable) oil has further increased the acidic compounds in bio-modified bitumen. Acidic compounds adsorb well to siliceous stones, but they are easily replaced by water molecules, giving rise to moisture damage. It was found that a reduction or removal of the acidic compounds of waste cooking oil via transesterification significantly enhances its resistance to moisture damage. The study results showed that treated waste cooking oil is not only a promising rejuvenator to be used with aged bitumen, but also quite resistant to moisture damage. It was also found that transesterification reduces the acid value of bitumen from 12 to 0.27 (mg KOH/g). This turned a moisture-susceptible bitumen to nearly a moisture-resistant bitumen as evidenced by nearly no change in moisture-induced shear thinning after 24hr water conditioning. The outcome of the study shows significant role of acidic compounds in moisture damage, and the importance of accounting for the acidity of rejuvenators to ensure their durability. The study results confirm the feasibility of tuning waste cooking oil to a sustainable asphalt rejuvenator to promote both resource conservation and asphalt recycling.

Reducing susceptibility to moisture damage in asphalt pavements using polyethylene terephthalate and sodium montmorillonite clay

This study examines the feasibility of developing built-in resistance against moisture damage using either passivation or an arresting mechanism. A specific moisture-susceptible paving mixture with proven moisture-damage issues in the field was selected for this study. The damage was attributed to failure at the interface of bitumen and stone aggregate due to accumulation of acidic compounds at the interface with subsequent dissolution in the presence of water. Here, we examine two remedial methods. The first method introduces a polyethylene terephthalate based additive (PET) to bitumen to neutralize active sites of stones with concentrations of silica oxide greater than 50% (denoted simply as siliceous stones), suppressing nucleation and growth of acids at the interface. The second method introduces sodium montmorillonite clay (MMT) to adsorb acids and prevent their migration to the interface of stone and bitumen. Measurement of shear binding between siliceous substrates and bitumen using a shear rate sweep test showed increases of 21% and 43% due to the inclusion of MMT and PET, respectively. This improvement was also observed in the results of bitumen bond-strength tests performed on glass and on stone substrates. Results of the evaluation at the mixture level using a Hamburg wheel-tracking test showed that the addition of MMT and PET improved resistance to moisture damage, as evidenced by the increasing number of cycles before moisture stripping occurs. For the PET-modified mixture, no stripping inflection was observed until 20,000 cycles. It was also observed that MMT’s adsorption of acidic compounds from bitumen led to the appearance of surface dents after water conditioning. The PET-modified specimen showed some signs of color change after water exposure, without any signs of stripping. The study results help formulators design materials with built-in resistance mechanisms against moisture damage.

New Archaeological Discoveries in The Geological Formations and Heritages along the Ba River Ancient Valley

In dry season of 2019, a series of new mix-heritages containing both of natural/geological and prehistoric archaeological values were discovered along the Ba river ancient valley by the field survey team of the project TN17/T06. The archaeological relics were uncovered right in the geological heritage sites such as: waterfalls, fossil sites, ancient terraces, and low mountain slopes along the Ba river ancient valley, which belong to eluvial, deluvial, proluvial and alluvial formations of Pleistocene age. Hundreds of stone tools, including dozens of petrified wood tools were collected, such as: uni-facial and bi-facial tools, end-chooper, side-chopper, scraper, spearhead tool, flake and core tools, etc. The materials of the tools were made of quartz, quartzite, siliceous stone, opal-chalcedony, petrified wood and basalt, which were recognized as geological heritages (A type: Paleontology; D type: Rock; F type: Minerals, according to the classification in the Circular 50/2017-TT-BTNMT of MONRE) of the heritage region. The collected artifacts characterise technique and geometric shape types of Paleolithic age. The archaeological discoveried sites were highly evaluated by Vietnamese and foreign archaeologists because they play a great important role in studying Paleolithic stage in Gia Lai province and The Central Highlands particularly, and in Vietnam and Southeast Asia generally. Besides, they have increased comprihensive heritage values of the region, as well as provided double invaluable resources (both natural and cultural heritage) for tourism exploitation and socio-economic sustainable development.

A bottom-up approach to study the moisture susceptibility of bio-modified asphalt

Causes and remedies for moisture damage at the interface of binder and siliceous stone aggregates is not fully understood and is considered as one of the most elusive and intractable pavement distresses. In recent years, increasing environmental awareness and decreasing availability of virgin materials have promoted the use of bio-materials to decrease adverse environmental impacts from petroleum-based products and support sustainable practices. Considering source dependency and composition variation in bio-materials, it is important to relate composition to fundamental materials properties in order to ensure adequate overall performance particularly in terms of resistance to moisture. Therefore, the current study uses a bottom-up approach to evaluate the performance of an asphalt binder additive from swine manure (Bio-modifier) as a means of not only improving but also understanding moisture resistance in asphalt pavement. Bio-modification was found to show improved moisture resistance at the binder level and the mixture level when compared to two other commercially available additives. Further analysis of the binder doped with representative molecules of the additives showed varying differences in adhesion and moisture susceptibility. To provide in-depth understanding of the underlying interaction mechanisms between water and binder, molecular dynamic simulations were performed on a blend of asphaltene and dopant molecules placed on a silica oxide substrate and exposed to water molecules. Study results revealed the passivation mechanism of bio-modifiers as a dominant factor contributing to enhanced resistance to moisture damage. It was found that bio-modifiers molecules occupy active sites of silica oxide preventing nucleation and growth of acidic compounds at the binder-silica interface. Such acidic compounds are water soluble and their presence at the interface can be detrimental leading to moisture damage. Study results showed anchored bio-modifiers molecules further interact with asphaltene molecules to provide bridging mechanism between binder and silica. This in turn leads to enhanced resistance to moisture damage in bio-modified binders adhered to siliceous surfaces such as quartz and granite stone aggregates.

Morphological characterization of water-based nanolime dispersions

This paper studies the morphological characteristics of calcium hydroxide nanoparticles in water based dispersions, produced following the main bottom-up (CaCl2/NaOH replacement reaction) and top-down methodologies. The work focuses on the effect of three different surfactants (TritonX-100, n-octylamine and amylamine) on the morphological characteristics of the resulting Ca(OH)2 nanoparticles and compares them with the ones produced in a mixture of water and 2-propanol. Moreover, in an attempt to approach the compatibility enhancement with siliceous stones, a calcium hydroxide—TEOS composite was also studied. The morphological, chemical and the mineralogical characterization of the nanoparticles produced were carried out by electron microscopy (SEM), dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). It is shown that the modifications induced by the production methodologies limited the agglomeration phenomena and altered the morphological characteristics of nanoparticles, when compared to the results obtained by the original bottom-up method, resulting in the synthesis of hexagonal, plate-like, rounded and angular portlandite nanoparticles. The size range of the nanoparticles extended from 60 to 350 nm.

Multiscale Evaluation of Moisture Susceptibility of Biomodified Bitumen.

This paper studies the selective adsorption and dewetting processes of various biomodifiers with respect to siliceous surfaces to determine dominant moisture damage mechanisms in bitumen doped with biomodifiers. Accordingly, it introduces four different biomodifiers made from various biomasses while explaining their differential effects on moisture susceptibility of bitumen when they are introduced to bitumen as a modifier to make commonly used biomodified binders. The biomodified binders studied here are made from extracts of biomass: wood pellets, miscanthus, corn stover, and animal waste. The moisture effect on biomodified bitumen was evaluated through contact angle measurement followed by molecular-level binding energy based on density functional theory (DFT). The change of contact angle between each biomodified bitumen and a silica surface when exposed to water was used as an indicator of the propensity for dewetting. The biomodifiers from animal waste showed the least change, followed by corn stover, wood pellet, and miscanthus. This aligns with our results of in situ Fourier transform infrared analysis, which showed that the biomodifier from miscanthus has the lowest adsorption affinity, while the one from animal waste has the highest adsorption onto siliceous stones. The higher adsorption efficiency of animal-based biomodifier is also verified by DFT-based molecular modeling, showing that the lipid and protein contents of animal waste, containing highly polar small compounds, exhibit a better adsorption to silica nanoparticles compared to carbohydrate of terrestrial plants.

Surface Geotechnical Weathering and denudation in the Northeast Margin of Tarim

The research region is located in the northeast margin of Tarim, which is characterized by a typical continental arid desert climate, with a scanty rainfall and large difference in temperature between day and night. The research region is relatively stable in geology and exposed to the long-term weathering and serious erosion of seasonal surface water, which lead to the typical landform of “planation surface” and Yadan. In order to investigate the long-term stability of superficial facilities in this region, a series of methods have been conducted to study the erosion characteristics of soil and rocks in some representative positions, i.e., soil erosion monitoring in different places, modelling analysis of soil erosion, terrestrial cosmogenic nuclides concentration measurement, denudation amount measurement of stone relics, and estimation of regional strata denudation. The results demonstrate that erosion rate is less than 0.3m/104a for sandstone in flat surface, 0.8 m/104a in seasonal gully. The erosion rate of soil is averagely 0.16∼0.19cm/a for palaeo-lacustrine deposition area since late pleistocene epoch, 0.42cm/a for monitoring platform, 3.97cm/a for erosional depression. The denudation rate is estimated to be 0.9 mm/104a for siliceous stone relics, 9.5∼11.6 mm/104a for sandstone and granite relics, and 4.0mm/a for ancient architecture made of soil in research area. By the method of tectonic trend of missing strata, it is estimated that the erosion rate is less than 0.35 m/104a since the tertiary period when a steady stage of uplift and denudation begin in the research region.

Composition and properties of Kazakhstani diatomaceous minerals and synthesis on their base calcium silicates for building production

The review covers existing modern technologies and researches on applying diatomaceous minerals as silicate additives to building materials. Specialists of industrially developed countries actively work in this direction and there are some of the works on the stage of implementation now. The article also describes researches of the authors on synthesis of calcium silicate and hydrated forms of ferro-calcium silicates using different kinds of Kazakhstani diatomaceous minerals from Zhalpak deposit (Aktobe region) as main siliceous component. Main topological and physical-and-mechanical characteristics of natural diatomaceous minerals were studied. It was found out that using thermally activated diatomite mixed with a plasticizing agent enlarges strength under compression and raises the brand of building materials while lowering water absorption and specific weight. It was observed that use of thermally activated highly ferriferous diatomite (20-30 % of Fe2O3) increases the strength of building materials dramatically. X-ray phase analysis of the samples of cubes from obtained composites exposed to semi-dry pressing with thermally activated ferrous diatomite followed by steam tempering showed that there were Ca(Fe, Mg)Si2 and FeAl2SiO5(OH)2 in their composition in the amount up to 1 mas. %.The technical characteristics of cubes of composition obtained with the use of thermally activated diatomite, in particular its highly ferriferrous forms, are completely meet requirements of inter-state standards GOST 379–95 to siliceous stones and bricks and sometimes overcome this norms. In future, the technology for obtaining the synthesized materials can become a base to organize new and to improve the existing industries producing dry building mixtures and strong silicate bricks in Kazakhstan.

Biological Oxidation and Removal of Iron in Copper-Containing Acidic Mine Drainage by Using Siliceous Stones as Carrier Materials

Acid mine drainage is detrimental to the environment, which is rich of a variety of heavy metals, and has a low pH value and high acidity. The purpose of this paper is to study the bio-oxidation of ferrous iron and the selective precipitation of ferric iron, to gain a long-term effective solution to the environmental problem. The maximum ferrous iron bio-oxidation rate (76.19mg/L·h) was obtained at a low pH value of 3.0 and culture temperature of 30°C. In addition, we found a relatively higher ferric iron removal rate (99.18%) and the lowest copper loss rate (4.59%) at a pH value of 3.2 and reaction temperature of 30°C and stirring time of 4h.

“Undatable, unattractive, redundant”? The Rapavi silcrete source, Saint-Pierre-Eynac (Haute-Loire, France): Challenges studying a prehistoric quarry-workshop in the Massif Central mountains

Silcretes are not widely discussed archaeologically as a prehistoric lithic resource in Europe, despite there being many years of geological research into their formation, and in some regions, a long record of their use in prehistory. In the Massif Central, south eastern France, various silcrete sources represent some of the largest and best quality siliceous stone sources within this otherwise volcanic area. Field research within a wider programme of landscape archaeology and lithic sourcing identified a quarry-workshop for one of these silcrete sources, at Rapavi, Saint-Pierre-Eynac (Haute-Loire).Archaeological and geological results are reported, discussing the technological behaviour uncovered at this locale and its wider regional connections, including the presence of imported flint artefacts. Additionally, the Rapavi silcrete provides an example of the challenges encountered when analysing raw materials with idiosyncratic fracture properties, and attempting to disentangle quarry-workshop palimpsests.

Assemblages with bifacial tools in Eurasia (third part). Considerations on the bifacial phenomenon throughout Eurasia

Eurasian bifacial series present some common features, but are chiefly characterized by wide-ranging diversity in terms of bifacial technology and blank types, whereas the heavy-duty component presents a limited number of types or categories. Heavy-duty tools are present throughout the geographical areas but the frequency of handaxes and/or cleavers is generally low, except in some regions, where they are made on flakes and/or cobbles/pebbles, on siliceous stones or other rock types. So far, it appears to be generally accepted that bifacial technology became widespread from 800 to 700ka onwards, both for Europe and Asia, except for some earlier occurrences in the Levant and India. It would thus be reasonable to infer that bifacial technology first reached the Levant from Africa before moving toward Asia, then Europe. However, the existing data point to a much more complex reality, suggesting contemporaneous technological worlds, with or without links between them. In the state of current knowledge, and based on the methodology used for analysing lithic series, it is impossible to clearly argue in favour of either a unique phenomenon with movements of hominins or/and ideas from an African source, or to point to evidence of several onsets of bifacial technology over time on a local substratum. The palaeoanthropological background shows the difficulties involved in characterizing the few available hominin fossils and clearly relating them to bifacial technology. The current context suggests that each area should be analysed independently. Accumulative technological processes in some areas due to successive arrivals and the influence of the local substratum, and local onsets must be considered, as these contribute to the diversity of the strategies encountered and the varied forms of bifacial technology.

Copper Age axe-hammers, other tools and their raw materials in the sub-Apenninic area east of Bologna (Italy)

During this study, about two hundred stone tools from the Bologna territory—particularly from the S. Lazzaro di Savena area—were studied. They comprise perforated axe-hammers, axes/adzes and other variously polished complete or fragmentary tools of Copper Age typology, mostly coming from surface survey. They are mostly manufactured from basic magmatic rocks (in order of abundance: diabases, dolerites, gabbros, basalts and basic porphyrites) typical of the Apennine ophiolites outcropping upstream to the local mountains/hills, as well as in several areas of the Northern Apennines. Other lithologies, such as ophiolitic ultramafics (serpentinites, steatite and one Ca-pyroxenite) and non-ophiolitic lithologies, are poorly represented. The petrographic features of the studied artefacts are compatible with those of the ophiolitic rocks outcropping in the nearby Apennines and include varying degrees of low-grade, both of continental (various green and bright amphiboles, chlorite, saussurrite etc.) and oceanic metamorphism (typically brown hornblende and rare mylonitic textures). Some basic porphyrites with large phenocrysts, uncommon in the Apennine ophiolites, are also present. The few non-ophiolitic lithologies (siliciclastic arenites, calcarenites, limestones and siliceous stones) were probably supplied from the nearby Apennine, with the exception of a spotted slate of unknown origin. Based on their morphotypological features, some ophiolitic and not-ophiolitic artefacts may suggest some exchange and importation from—or simply some prehistoric cultural links with—Tuscany, Marche and occasionally Southern Italy and South Tyrol/Alto Adige.

Calcium carbonate precipitation by heterotrophic bacteria isolated from biofilms formed on deteriorated ignimbrite stones: influence of calcium on EPS production and biofilm formation by these isolates

Heterotrophic CaCO3-precipitating bacteria were isolated from biofilms on deteriorated ignimbrites, siliceous acidic rocks, from Morelia Cathedral (Mexico) and identified as Enterobacter cancerogenus (22e), Bacillus sp. (32a) and Bacillus subtilis (52g). In solid medium, 22e and 32a precipitated calcite and vaterite while 52g produced calcite. Urease activity was detected in these isolates and CaCO3 precipitation increased in the presence of urea in the liquid medium. In the presence of calcium, EPS production decreased in 22e and 32a and increased in 52g. Under laboratory conditions, ignimbrite colonization by these isolates only occurred in the presence of calcium and no CaCO3 was precipitated. Calcium may therefore be important for biofilm formation on stones. The importance of the type of stone, here a siliceous stone, on biological colonization is emphasized. This calcium effect has not been reported on calcareous materials. The importance of the effect of calcium on EPS production and biofilm formation is discussed in relation to other applications of CaCO3 precipitation by bacteria.