Quartz Grain Size Research Articles

Structural and rheological features of the western Liaoning metamorphic core complex corridor: Indications for Late Mesozoic extension of the eastern North China Craton

The Xingcheng-Taili ductile shear zone and Yiwulüshan metamorphic core complex formed during crustal extension of the eastern North China Craton. The ENE-trending Xingchegn-Taili sinistral ductile shear zone developed along the margins of the western Liaoning metamorphic core complex corridor within upper greenschist to lower amphibolite facies-grade metamorphic conditions. Shearing was associated with two different ductile deformation events in the Yiwulüshan metamorphic core complex, i.e. (1) an earlier dextral shearing and (2) later sinistral shearing. The earlier dextral ductile shear zone is mainly characterized by simple-shear dominated general shear with L=S and LS tectonites under upper greenschist to lower amphibolite facies conditions. The orientation and fabrics of L=S tectonites indicate that the later ductile deformation consists of almost equally simple and pure shear and constrains a low-middle-temperature sinistral shear within upper greenschist facies-grade conditions. The estimation of rock rheological parameters from dynamically recrystallized grain sizes of quartz indicates that the high-temperature shear zone has formed under lower stress conditions and higher strain rates, while opposite features exist in the lower temperature shear zone. The initiation of deformation of the western Liaoning metamorphic core complex corridor might have started between 136Ma and 120Ma and its termination time was at ca. 100Ma. The NE-ENE strike-slip ductile deformation in the western Liaoning metamorphic core complex corridor, within the Eastern Block of the North China Craton, was resulted from roll-back of the subducting Pacific plate beneath the North China Craton along the eastern Asian margin during Early Cretaceous times.

Influence of the physico-mechanical and mineral properties of various marble on diamond tool wear

Experimental studies were performed on five different marble samples, namely Makarana white, Bhainslana black, Andhi white, Udaipur sea green and Agaria white to know the influence of their mineral and physico-mechanical properties on the specific wear of the tool. To achieve this sawing experiment were performed in down cutting mode on different marble samples to find the wear rate of the tool. Marble samples were tested in the laboratory to find their mechanical properties according to ASTM standards, the further micro-structural characterisation was carried out using thin sections and was observed under a polarised microscope for identifying the mineral composition, grain size distribution, and other textural information. Statistically tested marble samples revealed that specific wear rate (SWR) increases with an increase in the grain size of quartz and lime unveiling them as dominating factors affecting wear. A weak correlation was found to be existing between the quartz content and SWR has been discussed. Except hardness, none of the other mechanical properties showed a significant correlation to SWR indicating that mechanical properties are not alone affecting the tool wear but also the mineral properties and their grain sizes.

Numerical modeling of mullions in the Taili high deformation zone, North China: Implications for the rheology of granitic rocks

This paper presents a combined field measurement and finite element modeling analysis of the mullions occurring on the contact of two granitic rocks with different grain size in the Taili High-Strain Deformation Zone (THDZ), West Liaoning of North China. All of the field data are located in the plot zone of the modeling results. Numerical modeling results indicate that: (1) The inter-angle between the tangent lines cross the cusp point and the ratio R of amplitude and width of mullions are the most effective parameters to describe the geometric shape and evolution of mullions, as well as useful indicators of the rheology of rocks. (2) The competence contrast controls the growth rate of mullions under shortening. It determines the possible ratio R of final mullions. Moreover, decreasing of the cusp angle in high competence contrast materials is faster than that in low competence contrast model. (3) The initial disturbance is an essential factor for the generation of mullions. Those contacts with higher initial disturbance will develop into mullions more easily and have a high growth rate during the same shortening deformation regime. (4) The rheology and deformation behavior of the granitic rocks in the study area are primarily controlled by the grain sizes of quartz and feldspar. The effective viscosity ratio of biotite adamellite and granitic gneisses is about 0.01–0.5. The deformation mechanisms of these granitic rocks should be dominated by a grain-size-sensitive diffusion creep.

Application of Image Analysis to Identify Quartz Grains in Heavy Aggregates Susceptible to ASR in Radiation Shielding Concrete.

Alkali-silica reaction (ASR) is considered as a potential aging-related degradation phenomenon that might impair the durability of concrete in nuclear containments. The objective of this paper is the application of digital analysis of microscopic images to identify the content and size of quartz grains in heavy mineral aggregates. The range of investigation covered magnetite and hematite aggregates, known as good absorbers of gamma radiation. Image acquisition was performed using thin sections observed in transmitted cross-polarized light with λ plate. Image processing, consisting of identification of ferrum oxide and epoxy resin, and the subsequent application of a set of filtering operations resulted in an adequate image reduction allowing the grain size analysis. Quartz grains were classified according to their mean diameter so as to identify the reactive range. Accelerated mortar bar tests were performed to evaluate the ASR potential of the aggregates. The SiO2 content in the heavyweight aggregates determined using the image analysis of thin sections was similar to XRF test result. The content of reactive quartz hematite was 2.7%, suggesting that it would be prone to ASR. The expansion test, according to ASTM C1260, confirmed the prediction obtained using the digital image analysis.

Sediment grain size and surface textural observations of quartz grains in late quaternary lacustrine sediments from Schirmacher Oasis, East Antarctica: Paleoenvironmental significance

In this study we report the sediment grain size parameters and surface textural observations (using scanning electron microscopy (SEM)) of quartz grains from sediments of Sandy Lake, Schirmacher Oasis, East Antarctica. The sediment core spans the last 43 cal ka B.P. The statistical parameters of grain size data (sorting, skewness, kurtosis, mean grain size, D10, D50, D90 and SPAN index) indicate that the sediments are primarily transported by melt-water streams and glaciers. However, during the last glacial period, sediments seem to be transported due to wind activity as evident by the good correlation between rounded quartz data and dust flux data from EPICA ice-core data. The mean grain size values are low during the last glacial period indicating colder climatic conditions and the values increase after the last glacial maximum suggesting an increase in the energy of the transporting medium, i.e., melt-water streams. The sediments are poorly sorted and finely skewed and show different modes of grain size distribution throughout the last 43 cal ka B.P. SEM studies of selected quartz grains and analyses of various surface textures indicate that glacigenic conditions must have prevailed at the time of their transport. Semi-quantitative analyses of mineral (quartz, feldspar, mica, garnet and rock fragments & other minerals) counts suggest a mixed population of minerals with quartz being the dominant mineral. Higher concentration of quartz grains over other minerals indicates that the sediments are compositionally mature. The study reveals the different types of physical weathering, erosive signatures, and chemical precipitation most of them characteristic of glacial environment which affected these quartz grains before final deposition as lake sediments. The palaeoclimatic signals obtained from this study show similarities with ice-core and lake sediment records from Schirmacher Oasis and other ice-free regions in East Antarctica.

Strain localization in brittle–ductile shear zones: fluid-abundant vs. fluid-limited conditions (an example from Wyangala area, Australia)

Abstract. This study focuses on physiochemical processes occurring in a brittle–ductile shear zone at both fluid-present and fluid-limited conditions. In the studied shear zone (Wyangala, SE Australia), a coarse-grained two-feldspar–quartz–biotite granite is transformed into a medium-grained orthogneiss at the shear zone margins and a fine-grained quartz–muscovite phyllonite in the central parts. The orthogneiss displays cataclasis of feldspar and crystal-plastic deformation of quartz. Quartz accommodates most of the deformation and is extensively recrystallized, showing distinct crystallographic preferred orientation (CPO). Feldspar-to-muscovite, biotite-to-muscovite and albitization reactions occur locally at porphyroclasts' fracture surfaces and margins. However, the bulk rock composition shows very little change in respect to the wall rock composition. In contrast, in the shear zone centre quartz occurs as large, weakly deformed porphyroclasts in sizes similar to that in the wall rock, suggesting that it has undergone little deformation. Feldspars and biotite are almost completely reacted to muscovite, which is arranged in a fine-grained interconnected matrix. Muscovite-rich layers contain significant amounts of fine-grained intermixed quartz with random CPO. These domains are interpreted to have accommodated most of the strain. Bulk rock chemistry data show a significant increase in SiO2 and depletion in NaO content compared to the wall rock composition. We suggest that the high- and low-strain microstructures in the shear zone represent markedly different scenarios and cannot be interpreted as a simple sequential development with respect to strain. Instead, we propose that the microstructural and mineralogical changes in the shear zone centre arise from a local metasomatic alteration around a brittle precursor. When the weaker fine-grained microstructure is established, the further flow is controlled by transient porosity created at (i) grain boundaries in fine-grained areas deforming by grain boundary sliding (GBS) and (ii) transient dilatancy sites at porphyroclast–matrix boundaries. Here a growth of secondary quartz occurs from incoming fluid, resulting in significant changes in bulk composition and eventually rheological hardening due to the precipitation-related increase in the mode and grain size of quartz. In contrast, within the shear zone margins the amount of fluid influx and associated reactions is limited; here deformation mainly proceeds by dynamic recrystallization of the igneous quartz grains. The studied shear zone exemplifies the role of syn-deformational fluids and fluid-induced reactions on the dominance of deformation processes and subsequent contrasting rheological behaviour at micron to metre scale.

Using EBSD Data to Analyze Effect of Heat Supplied by Granite on CPO of Quartz in Deformed Quartzite

Abstract Electron Backscatter Diffraction (EBSD) data of quartz are presented from two quartzite samples of the Lunavada Group (Aravalli Mountain Belt, India). The two samples lie at a distance of 4 km and 30 km from the eastern margin of Godhra granite, which is known to have emplaced syntectonically with late deformation of the Lunavada Group rocks. The sample located away from the granite has weak CPO and fine grain size. Quartz grains in the sample close to the granite are coarse and show strong CPO. It is concluded that heat supplied by the Godhra granite resulted in coarsening of grain size, and dislocation creep was an important deformation mechanism in the sample proximal to the granite. Weak CPO in sample away from granite maybe due to grain boundary sliding, which may have been favoured by the finer grain size of quartz in the sample.

Feature and duration of metre-scale sequences in a storm-dominated carbonate ramp setting (Kimmeridgian, northeastern Spain)

Metre-scale sequences may result from the combined effects of allocyclic and autocyclic processes which are closely inter-related. The carbonate ramp that developed northwest of the Iberian Basin during the late Kimmeridgian was affected by northwestward migrating cyclones. Marl–limestone alternations that settled in mid-ramp environments contain abundant mm to cm thick coarse-grained accumulations that have been related to these events. The aim of this paper is to determine the impact of storm-induced processes on the metre-scale sequence features. Four sections (R3, R4, R6, and R7), which are 5 to 7m in thickness, were studied bed-by-bed along a 4km-long outcrop, which shows the transition between the shallow and the relatively deep realms of the middle ramp. Metre-scale sequences were defined and correlated along this outcrop according to the detailed microfacies analysis of host, fine-grained deposits, palynofacies and sequence-stratigraphic analyses, and carbon- and oxygen-isotope measurements. The evolution through time of sedimentary features such as the size of quartz grains and the relative abundance of grains other than quartz (i.e., muscovite, bivalve, ooid, and intraclast) does not correlate from one section to the other, suggesting that the finest as well as the coarsest sediment was reworked in these storm-dominated environments. Small- and medium-scale sequences are defined according to changes in alternation, marly interbed, and limestone bed thickness, and correlated from one section to the other. Because of the effects of storms on sediment distribution and preservation, sequence boundaries coincide with thin alternations and marly interbeds in the most proximal sections (i.e., R3, R4), while they correspond to thin alternations and limestone beds in the most distal sections (i.e., R6, R7). Field observations and palynofacies analyses confirm this sequence-stratigraphic analysis. The excursions in carbon- and oxygen-isotope values are consistent with the lithological correlations, but in themselves are not conclusive. Marl–limestone alternations, and small-, and medium-scale sequences are hierarchically stacked, suggesting an orbital control on sedimentation with alternations lasting 20kyr, small-scale sequences, 100kyr, and medium-scale sequences, 400kyr. As biostratigraphic analyses and spectral analysis are not the most appropriate tools to validate this time calibration in such a short interval and highly dynamic system, an alternative approach is developed, which is based on the quantification of the rates of sediment accumulation, preservation, and sea-level rise.

Fine and coarse-quartz SAR-OSL dating of Last Glacial loess in Southern Romania

Previous single aliquot regenerative optically stimulated luminescence (SAR-OSL) dating studies of representative loess sections in southeastern Romania revealed severe discrepancies among the ages obtained on fine (4–11 μm) and coarse (63–90 μm) grains of quartz. The current study aims at expanding these investigations by extending the area of study to the more westerly loess deposits in the Lower Danube Basin. The luminescence properties of the grain sizes of quartz extracted from 18 samples collected from the Last Glacial loess layer at Lunca section (Wallachian Plain) are examined and compared. Investigations confirm the reliability of the SAR-OSL protocol previously applied to Romanian loess (preheat at 220 °C for 10 s, cutheat at 180 °C and elevated temperature OSL). Despite this, the obtained equivalent doses on coarse quartz are higher than those obtained on fine material for most samples, as in the case of our previous studies. These results into fine quartz OSL ages that are significantly lower compared to the coarse quartz age results. However, the ages obtained for the uppermost two samples are in very good agreement. Ages spanning from 19 ± 2 ka to 43 ± 4 ka on fine quartz and from 20 ± 2 ka to 54 ± 6 ka on coarse quartz have been obtained for the loess deposited during Last Glacial period. Based on the fine as well as the coarse quartz chronology significantly low sedimentation rates were computed for the Last Glacial Maximum period and MIS 3. OSL ages and magnetic susceptibility measurements indicate that the loess layer corresponding to the Early Glacial period (MIS 4) is very thin at this site and affected by pedogenesis. Regarding the investigation into the cause of the observed age discrepancy we present evidence through time resolved investigations that the observed behaviour is typical of quartz and cannot be accounted by feldspar contamination. We confirm once more that the growth of the OSL signal in nature does not correspond to the laboratory generated SAR dose response curve that is best described by a sum of two saturating exponential functions. The differences observed between the natural and the laboratory dose response for the two quartz fractions are believed to be a cause for the different chronologies reported.

On natural and laboratory generated dose response curves for quartz of different grain sizes from Romanian loess

One of the most important foundations of luminescence dating is the assumption that the growth of the luminescence signal in nature can be reproduced under laboratory conditions by performing irradiations with a calibrated beta or gamma source. When optically stimulated luminescence (OSL) of quartz with a dominant fast component is measured using the single aliquot regenerative dose (SAR) protocol, laboratory dose response curves that display continuing growth at high doses are increasingly reported in literature. In this study we investigate fine (4–11 μm) and coarse (63–90 μm) quartz extracted from 25 samples taken from L1, S1 and L2 units from the loess-palaeosol section at Costineşti in Romania. Our results indicate that the growth of the OSL signal in nature does not correspond to the laboratory generated laboratory dose response curve. The growth of the signal in nature is consistent with a single saturating exponential function, with the signal of coarse grains starting to saturate at 100–200 Gy, and for fine grains at 200–300 Gy, respectively. Laboratory dose response curves continue to grow for high doses (>300 Gy) for both quartz fractions. The differences observed between the natural and the laboratory dose response for the two quartz fractions are believed to be a cause for the different chronologies previously reported using the two grain sizes of quartz on Romanian loess. In addition, we have applied the single aliquot regeneration and added dose (SARA) procedure to both fine and coarse grains from the youngest sample. Our findings question the reliability of obtaining high equivalent doses for quartz samples displaying laboratory dose response curves obtained by the SAR protocol for which a single saturating exponential model does not describe the data.

Paleoenvironments during the Rhaetian transgression and the colonization history of marine biota in the Fatric Unit (Western Carpathians)

Abstract Terminal Triassic environmental changes are characterized by an integrated study of lithology, litho- and cyclostratigraphy, paleontology, mineralogy, geochemistry and rock magnetism in the Tatra Mts. The Carpathian Keuper sequence was deposited in an arid environment with only seasonal rivers, temporal lakes and swamps with scarce vegetation. Combination of a wide range of δ18O values (-0.7 to + 2.7) with negative δ13C values documents dolomite precipitation either from brackish or hypersaline lake water, or its derivation from pore water comparably to the Recent Coorong B-dolostone. Negative δ13C values indicate microbial C productivity. Rhaetian transgressive deposits with restricted Rhaetavicula fauna accumulated in nearshore swamps and lagoons. Associations of foraminifers, bivalves and sharks in the Zliechov Basin were controlled by physical factors. Bivalve mollusc biostromes were repetitively destroyed by storms, and temporary firm bottoms were colonized by oysters and burrowers. Subsequent black shale deposition recorded input of eolian dust. Bottom colonization by pachyodont bivalves, brachiopod and corals started much later, during highstand conditions. Facies evolution also revealed by geochemical data, C and O isotope curves reflect eustatic and climatic changes and help reconstruct the evolution of Rhaetian marine carbonate ramp. The Fatra Formation consists of 100 kyr eccentricity and 40 kyr obliquity cycles; much finer rhythmicity may record monsoonlike climatic fluctuations. Fluvial and eolian events were indicated by analysis of grain size and content of clastic quartz, concentrations of foraminiferal (Agathammina) tests in thin laminae indicates marine ingression events. Magnetic susceptibility (MS) variations reflect the distribution of authigenic and detrital constituents in the sequence. Increasing trend of MS correlates with the regressive Carpathian Keuper sequence and culminates within the bottom part of the Fatra Formation. Decreasing trend of MS is observed upwards the transgressive deposits of the Fatra Formation.

Geological setting and sedimentary characteristics of the coversands distributed in the western part of the Blonie glaciolacustrine basin (Central Poland) - Preliminary results

The coversands distributed in the Blonie glaciolacustrine basin, west of Warsaw (Central Poland) were investigated. Textural features including grain size, rounding and frosting of quartz grains and mineralogical-petrographic composition in the sandy fractions (0.5– 0.8 and 0.8–1.0 mm) were examined and the types, dynamics, regime and variation in processes during the formation of the coversands were determined. The sands are characterized by the prevalence of quartz and lack of micaceous minerals. Moreover, the relatively high content of partially rounded, matt (EM/RM) and well-rounded (RM) quartz grains, typical of aeolian sedimentary conditions, was certified. Hence, the results show a high aeolization degree of the investigated sediments, thus correlating them with aeolian deposition in dry, periglacial conditions after drying up of the Warsaw icedammed lake.

The formation of 1.13 nm tobermorite under hydrothermal conditions: 1. The influence of quartz grain size within the system CaO–SiO2–D2O

The influence of grain size of quartz on the formation of 1.13 nm tobermorite in aerated autoclaved concrete was investigated by applying in-situ neutron diffraction. Experiments were performed at 210 °C/Psat employing quartz of 8 μm and 16 μm, respectively. The results reveal changes in the reaction mechanism from solution control to diffusion control. The grain size of the quartz fraction clearly influences the occurrence of those changes. Based on those results an interpretation of former not clearly interpretable quenching experiments was performed. An interpretation using different reaction mechanisms for those experiments leads to a coherent picture of the reaction.

Testing the potential of elevated temperature post-IR IRSL signals for dating Romanian loess

In this study we test the potential of the elevated temperature infrared stimulated luminescence (IRSL) signals for dating Romanian loess. The recently developed post-IR IRSL protocol is applied to Romanian loess using polymineral fine grains extracted from the loess-palaeosol sequence at Mircea Vodă (SE Romania). This approach is aimed at obtaining an additional age control to examine the age discrepancy obtained from previous optically stimulated luminescence (OSL) studies using different grain-sizes of quartz (4–11 μm and 63–90 μm).Two preheat post-IR IR stimulation temperature combinations were used, 250–225 °C and 325–300 °C, respectively. The signals obtained are documented in terms of dose response curve, laboratory tests and fading. Although both post-IR IRSL signals exhibit small fading rates, dose response characteristics indicate that these rates may be laboratory artefacts. The post-IR IRSL signal stimulated at 300 °C is observed to suffer from dose dependent initial sensitivity changes as both natural and regenerated signals are observed to lie above the saturation level of the dose response curve. Uncorrected age results obtained using both post-IR IRSL signals are in general agreement with previously reported silt-sized quartz OSL ages for samples collected from the uppermost loess unit L1. For older material, the post-IR IRSL signal stimulated at 225 °C is considered to provide reliable age results, in agreement with independent age control available for this sequence.

Combined IRSL and post-IR OSL dating of Romanian loess using single aliquots of polymineral fine grains

The paper reports on continuing luminescence investigations of Romanian loess using samples collected from the loess-palaeosol sequence near Mircea Vodă (SE Romania). Previous optically stimulated luminescence (OSL) studies using different grain-sizes of quartz (4–11μm and 63–90μm) yielded discrepant chronologies for the last interglacial–glacial cycle. In this study, a double-SAR protocol is used to determine the age of polymineral fine (4–11μm) grains through their infrared stimulated luminescence (IRSL) and post-IR optically stimulated luminescence (post-IR OSL) emissions in the UV. Laboratory tests confirm the suitability of the protocol for both signals. Fading measurements indicate a significant feldspathic contribution to the post-IR OSL signal. In general, the fading-corrected IRSL and post-IR OSL age results are mutually consistent, and they agree with previously reported OSL ages for fine-grained (4–11μm) quartz. This agreement enhances the reliability of the ages obtained using luminescence signals from fine-grains, and allows more confident correlation of the weakly-developed palaeosol in the uppermost loess unit (L1) with marine isotope stage 3 (MIS3). The fading-corrected ages underestimate the depositional age of older material (units L2–L4), probably owing to limitations of the correction model.

Dry and strong quartz during deformation of the lower crust in the presence of melt

[1] Granulite facies migmatitic gneisses from the Seiland Igneous Province (northern Norway) were deformed during deep crustal shearing in the presence of melt, which formed by dehydration melting of biotite. Partial melting and deformation occurred during the intrusion of large gabbroic plutons at the base of the lower crust at 570 to 520 Ma in an intracontinental rift setting. The migmatitic gneisses consist of high-aspect-ratio leucosome-rich domains and a leucosome-poor, restitic domain of quartzitic composition. According to thermodynamic modeling using synkinematic mineral assemblages, deformation occurred at T = 760°C–820°C, P = 0.75–0.95 GPa and in the presence of ≤5 vol % of residual melt. There is direct evidence from microstructural observations, Fourier transform infrared measurements, thermodynamic modeling, and titanium-in-quartz thermometry that dry quartz in the leucosome-poor domain deformed at high differential stress (50–100 MPa) by dislocation creep. High stresses are demonstrated by the small grain size (11–17 μm) of quartz in localized layers of recrystallized grains, where titanium-in-quartz thermometry yields 770°C–815°C. Dry and strong quartz forms a load-bearing framework in the migmatitic gneisses, where ∼5% melt is present, but does not control the mechanical behavior because it is located in isolated pockets. The high stress deformation of quartz overprints an earlier, lower stress deformation, which is preserved particularly in the vicinity of segregated melt pockets. The grain-scale melt distribution, water content and distribution, and the overprinting relationships of quartz microstructures indicate that biotite dehydration melting occurred during deformation by dislocation creep in quartz. The water partitioned into the segregated melt crystallizing in isolated pockets, in the vicinity of which quartz shows a higher intracrystalline water content and a large grain size. On the contrary, the leucosome-poor domain of the rock, from which melt was removed, became dry and thereby mechanically stronger. Melt removal at larger scale will result in a lower crust which is dry enough to be mechanically strong. The application of flow laws derived for wet quartz is not appropriate to estimate the behavior of such granulite facies parts of the lower crust.

Chrysoprase from Gumigil, Queensland

Chrysoprase from Gumigil, near Marlborough in central east Queensland, occurs in weathered ophiolite of the Marlborough Block, in veins up to 20 cm thick in the lower parts of an approximately 50 m-thick regolith profile. Serpentinised harzburgite saprolite hosting magnesite and chalcedony veins with rare chrysoprase grades upward to a plasmic zone of chalcedony, nontronite and chlorite, with a lateritised zone above consisting of nodular or vermiform ferruginous duricrust, boxwork chalcedony and kaolinite. Gem chrysoprase and the poorer quality so-called ‘wetstone’ are dominantly chalcedonic quartz, coloured by willemseite, which occurs as 30–100 nm-wide zones largely aligned on polycrystalline quartz grain boundaries. Individual willemseite flakes (possibly single crystals) range from 2 to 12 nm thick. The quartz grainsize in chrysoprase is finer than in wetstone, and the willemseite domains in chrysoprase are smaller and less abundant, amounting to about 5% in chrysoprase and 15% in wetstone. Willemseite composition varies slightly between samples, with an average formula (Ni2.7Mg0.3)Si4O10(OH)2.

Chemical corrosion of sanitary glazes of variable grain size composition in acid and basic aqueous solution media

Glazes are responsible for the majority of the final surface properties of ceramic products, including their chemical corrosion resistance in contact with solutions of either acid or alkaline reaction. It is known that by adjusting their molar compositions it is possible, to some extent, to control the reactivity of glazes with such solutions. However, the allowable range of molar composition changes is limited, because this would, at the same time, modify other glaze parameters, such as fusibility, colour, gloss, or hardness. The investigation results presented in the article demonstrate that there is a potential for a significant improvement in the chemical corrosion resistance and other surface parameters of glazes through selecting the grain size of particular groups of raw materials used. On the example of glazes intended for sanitary products it has been proved that the proper selection of the grain size of quartz, feldspars and all rest raw materials results in a distinct reduction of the degree of corrosion caused by the action of water solutions of NaOH and HCl.

Development of a recrystallized grain size piezometer for hematite based on high-temperature torsion experiments

A series of hematite samples (>98 % Fe 2 O 3, Sishen Mine, South Africa) with different initial grain sizes of −5 s −1 and 4.7 × 10 −5 s −1 , resulting in finite shear strains between 0.4 and 4.7 and finite shear strengths in the range of 32–326 MPa. The data obtained at high shear strain (>3) fit to a power law creep equation with a pre-exponential constant of lnA = −5.03 ± 0.61 MPa −2.5 s −1 , an activation energy of Q = 249 ± 48 kJ mol −1 , and a stress exponent of n = 2.5 ± 0.5, indicating dislocation creep partially assisted by grain boundary sliding as the main deformation mechanism. Irrespective of the initial grain size, the final grain size ( D ) of fully recrystallized samples decreases continuously with increasing (steady state) equivalent stress (σ), yielding a piezometric relationship of the form: D = 1055 × σ 1.03 ± 0.10 . The piezometer is applied to itabiritic hematite ores of the Iron Quadrangle, Minas Gerais, Brazil, consisting mainly of layered hematite and quartz. Compared to hematite the measured recrystallized grain size of quartz is always larger, which is in agreement with the grain size range predicted by recrystallized grain size-based piezometers for hematite and quartz if deformed at similar stress below about 100 MPa.

An investigation of the petrographic and physico-mechanical properties of true granites influencing diamond tool wear performance, and development of a new wear index

Abstract An experimental study was carried out with the intent of establishing the most significant rock properties influencing sawblade wear performance in the processing of ‘true’ granites. To achieve this goal, microstructural characterization of nine different rock samples was made on thin sections using polarized petrographic microscope for the determination of mineral modal composition, grain size distribution and other textural features. The samples were also tested for their physico-mechanical properties. Sawing experiments of the studied rocks were performed on a full-scale side-cutting machine, and specific wear rate SWR was adopted as the criteria for sawblade wear performance. Statistical analysis of the experimental data indicated maximum grain size of quartz and alkali feldspar minerals (orthoclase/microcline) to be the most dominant factors influencing SWR . Despite its similar mineralogical hardness to alkali feldspar, the non-existence of a correlation between plagioclase feldspar (albite/oligoclase) grain size and SWR was discussed. A relatively weak correlation found between quartz content and SWR indicated that quartz content alone might not be a major contributor to sawblade wear performance. Except Shore hardness, none of the tested physico-mechanical rock properties showed a statistically significant correlation to SWR , suggesting that the physico-mechanical properties might not be a good indicator of diamond tool wear performance. Valid for the tested granite types and sawing conditions, a newly developed petrography-based prediction model of the SWR , named Specific Wear Rate Index was introduced. The high correspondence between the laboratory-measured and calculated SWR values using the presently developed wear index suggests that, if confirmed by further studies, it can be used as a guide for preliminary wear performance estimations in the circular sawing of true granites.