Coarse-grained Marble Research Articles

Strength estimation of granular rocks using a microstructure-based empirical model

A natural rock is an assembly of various mineral grains, and the microscopic grain structure of the rock influences its strength. The strength of granular rocks can be related to microscopic grain structure; however, empirical models linking microscopic grain structure and rock strength are rarely reported. This research presents a characterization method for geometric heterogeneity induced by the grain size difference. The heterogeneity of the microscopic scanning images of a coarse-grained marble is analyzed using a proposed heterogeneity index. A microstructure-based empirical model is proposed to describe the relation between the compressive strength of rock and its micro-property parameters. This microstructure-based empirical model is verified using numerical and experimental test data. The analysis results show that the proposed model can predict the strength of a granular rock better than existing models of similar nature. The model parameters for different rocks such as LdB granite, Aminadav dolomite, and Bohemian Massif granite are obtained by nonlinearregressionanalysis. This model is also employed to predict crack initiation and damage stresses of rocks, showing results in good agreement with the experimental data.

Consolidating efficacy of diammonium hydrogen phosphate on artificially aged and naturally weathered coarse-grained marble

• Naturally weathered marble in granular disintegration has increased porosity. • Artificially aged marble in granular disintegration was obtained by heating. • DAP can successfully consolidate weathered coarse-grained marble. • DAP efficacy is comparable on artificially aged and naturally weathered marble. • DAP improves the condition of marble from Roman Villa of Pisões. The effects induced by diammonium hydrogen phosphate (DAP) on coarse marble varieties susceptible to granular disintegration as consolidation material is still poorly addressed. The work aims at investigating the behavior and efficacy of diammonium hydrogen phosphate(DAP)-based consolidant prepared in laboratory onto weathered coarse-grained marbles and, in the process, to unveil if the treatment investigated is a possible option to consolidate Trigaches marble elements from Roman Villa of Pisões. Sound, artificially and naturally weathered coarse marble samples were used for the purpose. The condition of naturally weathered marble slabs was assessed to reproduce artificially aged samples and used for testing the efficacy of DAP consolidant. Naturally weathered slab fragments showed a uniform damage in depth, an increased porosity and water absorption, and very similar conditions were successfully achieved in laboratory by heating sound marbles up to 300 °C for 1 h. DAP consolidant has low viscosity and can easily penetrate within the porous structure of coarse marble in granular disintegration. It promotes the formation of new calcium phosphate phases with binding capabilities that partially restore cohesion in-depth. Alteration of the color was negligible which is also a positive characteristic. Pilot tests in naturally weathered marbles revealed some interference of superficial bioorganisms residues in the absorption of DAP, however this was able to treat the entire thickness of the slab fragments, improving its cohesion state to an acceptable or good condition. Good correlations between the results of artificial aged samples with those of naturally weathered marble were achieved and the DAP-based treatment revealed to be an effective option to consolidate Trigaches marble elements from Roman Villa of Pisões.

Prediction of weathering by thermal degradation of a coarse-grained marble using ultrasonic pulse velocity

Engineering properties of building stones can vary because of degradation by weathering agents. Thermal fluctuation is one of the most important agents on deteriorations such as sugaring, bowing, cracking and spalling of marble. As a result, physical and mechanical properties of marble used in the construction of old and/or modern structures are adversely affected by time. On the other hand, some properties of building stones are always required for decision of rehabilitation works. Several kinds of conventional tests have been suggested for characterization of stones, to measure their properties or to evaluate conservation or repair works. However, in most cases, sampling from historical buildings is not possible. Therefore, nondestructive testing methods are often suggested for the prediction of weathering grade of building stones. One of the most practical methods for similar purposes is ultrasonic pulse velocity measurement, which can be performed easily. The main goal of this study is attainment of sound empirical correlations between the ultrasonic pulse velocity and engineering properties of previously deteriorated marble. Experimental works were conducted on seven different specimen categories of a coarse-grained marble having different micro-crack frequencies induced by both cyclical heating–cooling and freeze–thaw actions. The experimental results indicated that physical and mechanical properties of Mugla marble can be reliably estimated for different environmental cases by ultrasonic pulse velocities. P-wave velocities in dry and saturated cases are two sound indicators of both the apparent porosity and the coefficient of capillary absorption, and whereby the sugaring type of deterioration for coarse-grained marbles.

Experimental Study on Relationship Between Mechanical, Seepage Characteristics and 3D Morphology Parameters of Marble Joint

In order to investigate the influence of 3D morphology parameters of marble joint surface on its mechanical and seepage characteristics, artificial joints of coarse-grained marbles were scanned by Tianyuan OKIO-typed 3D laser scanner; and then, the professional software was used to obtain the 3D morphology parameters of marble joint surface. Tests of water flowing through a single joint were conducted under different normal stress and feeding water head by using self-developed radial flowing system, and the exponential function between flow rate per head and normal stress, the linear relation between equivalent hydraulic aperture and mechanical aperture, and the linear relation between joint closure and normal stress were obtained. The relationships between regression parameters in above three formulas and 3D morphology parameters of joint surface were also studied by fitting method. All in all, the results may provide a reference to understand the mechanical and seepage characteristics of rough rock joint.

Influence of high strain rate deformation on40Ar/39Ar mica ages from marble mylonites (Syros, Greece)

Interpreting isotopic ages as deformation ages when they are acquired from moderate-temperature metamorphic environments can be a challenging task. Syros Island (Cyclades, Greece) is famous for Eocene high-pressure metamorphic rocks reworked by localized Miocene greenschist-facies deformation. In this work, we investigate phengites from coarse-grained marbles, which experienced the high-pressure event, and phengites from fine-grained localized marble shear zones attributed to the low-grade Miocene deformation. Based on structural criteria, both events can be easily discriminated because of their opposing kinematics. Laser-heating 40Ar/39Ar analysis on phengite yielded a 40 ± 1.6 Ma age for the host rock and a 37 ± 1.3 Ma age for the shear zone. Both ages are statistically indistinguishable, consistent with the regional Eocene event, and not the Miocene deformation event responsible for the formation of the shear zone. Thermodynamic modeling indicates that the observed high-variance mineral assemblage is stable without compositional change along the pressure-temperature path followed by the rocks of Syros. Although the marble within the shear zone was deformed at extremely fast strain rates (10−10 s–1), we observed no intracrystalline deformation of phengite grains and no resetting in the isotopic system, because strain was mostly accommodated by calcite. Consequently, a high strain rate does not necessarily create deformation ages in rocks with high-variance assemblages, such as marble mylonites.

Microstructures of coarse-grained marbles, analyzed using a new technique based on the bireflectance of calcite

A new approach to quantify microstructures of coarse-grained marbles is presented. This technique is based on the intensity of light reflectance in dependence of the crystallographic orientation of calcite grains. The technique setup consists of a high-resolution camera, a strong light source and the polished sample in reflection position. Microstructural data obtained with this method are comparable with those obtained by light microscopy or by secondary electron microscopy. However, the new approach reflects the grain size distribution even more accurately than in the case of other techniques, because it allows an easy quantification of larger sample surfaces. Therefore, in contrast to established techniques, microstructural analysis and statistics can also be performed for coarse-grained samples with grains that exceed diameters of 1 cm. With this new technique, coarse-grained mylonitic microstructures from Naxos were quantified, which in turn allowed relating different microfabrics to different strain localization episodes within a large-scale shear zone complex.

Low‐Temperature Plasticity of Naturally Deformed Calcite Rocks

AbstractOptical, cathodoluminescence and transmission electron microscope (TEM) analyses were conducted on four groups of calcite fault rocks, a cataclastic limestone, cataclastic coarse‐grained marbles from two fault zones, and a fractured mylonite. These fault rocks show similar microstructural characteristics and give clues to similar processes of rock deformation. They are characterized by the structural contrast between macroscopic cataclastic (brittle) and microscopic mylonitic (ductile) microstructures. Intragranular deformation microstructures (i.e. deformation twins, kink bands and microfractures) are well preserved in the deformed grains in clasts or in primary rocks. The matrix materials are of extremely fine grains with diffusive features. Dislocation microstructures for co‐existing brittle deformation and crystalline plasticity were revealed using TEM. Tangled dislocations are often preserved at the cores of highly deformed clasts, while dislocation walls form in the transitions to the fine‐grained matrix materials and free dislocations, dislocation loops and dislocation dipoles are observed both in the deformed clasts and in the fine‐grained matrix materials. Dynamic recrystallization grains from subgrain rotation recrystallization and subsequent grain boundary migration constitute the major parts of the matrix materials. Statistical measurements of densities of free dislocations, grain sizes of subgrains and dynamically recrystallized grains suggest an unsteady state of the rock deformation. Microstructural and cathodoluminescence analyses prove that fluid activity is one of the major parts of faulting processes. Low‐temperature plasticity, and thereby induced co‐existence of macroscopic brittle and microscopic ductile microstructures are attributed to hydrolytic weakening due to the involvement of fluid phases in deformation and subsequent variation of rock rheology. During hydrolytic weakening, fluid phases, e.g. water, enhance the rate of dislocation slip and climb, and increase the rate of recovery of strain‐hardened rocks, which accommodates fracturing.

How grey limestones become white marbles

The conditions required for generating white marbles are investigated in the contact aureole of the Adamello Pluton in northern Italy, where grey limestones pass into white marbles with increasing metamorphic grade. The grey-level or whiteness of the carbonate rocks is quantitatively measured using an integrating sphere, and values are linked to the mineralogical components and textural features. Nearly pure calcite rocks (> 99 wt % CaCO 3 ) undergo a transition from dark and light-grey very-low-grade metamorphic limestones to white and dull white marbles close to the intrusive contact. The grey colour of the limestones is caused by as little as 0.05 wt % of finely dispersed organic carbon. Approaching the pluton, the organic carbon content decreases with increasing metamorphic grade, producing a pure white to dull white marble with less than 0.02 wt % of organic carbon. Grain size and grain-boundary width have a secondary control on the appearance of high-grade white marbles by controlling light absorption, and thus brightness as well. The photon path is longer leading to higher absorption in coarse-grained marbles, thus explaining their dull appearance. Otherwise, changes in refractive index caused by wide grain boundaries are believed to enhance the light reflection in statically recrystallised marbles compared with very-low-grade metamorphic limestones which appear darker. Secondary phases such as silica or ore minerals, or significant fluid flow, do not induce colour changes.

Timescales and mechanisms of fluid infiltration in a marble: an ion microprobe study

Using a recently developed ion microprobe technique, a detailed oxygen isotope map of calcite grains in a coarse-grained marble has been constructed, supported by trace element (Mn, Sr, Fe) analysis and cathodoluminescence (CL) imaging, in order to constrain scales of oxygen isotope equilibrium, timescales and mechanisms of metamorphic fluid infiltration, and fluid sources and pathways. Results are compared with a previous study of this sample (Wada 1988) carried out using a cryo-microtome technique and conventional oxygen isotope analysis. The marble, from the high temperature/low pressure Hida metamorphic belt in north-central Japan, underwent granulite facies followed by amphibolite facies metamorphic events, the latter associated with regional granite intrusion. The CL imaging indicates two types of calcite, a yellow luminescing (YLC) and a purple luminescing (PLC) variety. The YLC, which occupies grain boundaries, fractures, replacement patches, and most of the abundant deformation twin lamellae, post-dates the dominant PLC calcite and maps out fluid pathways. Systematic relationships were established between oxygen isotope and trace element composition, calcite type and texture, based on 74 18O/16O and 17 trace element analyses with 20–30 μ m spatial resolution. The YLC is enriched in Mn and Fe, and depleted in 18O and Sr compared to PLC, and is much more 18O depleted than is indicated from conventional analyses. Results are interpreted to indicate infiltration of 18O-depleted (metamorphic or magmatic) fluid (initial δ18O = 9‰–10.5‰) along grain boundaries, fractures and deformation twin lamellae, depleting calcite grains in Sr and enriching them in Mn and Fe. The sample is characterised by gross isotopic and elemental disequilibrium, with important implications for the application of chromatographic theory to constrain fluid fluxes in metacarbonate rocks.

A microstructure-based failure criterion for Aminadav dolomites

A natural rock is an assembly of various mineral grains, and the microscopic grain structure of the rock influences its strength. The strength of granular rocks can be related to microscopic grain structure; however, empirical models linking microscopic grain structure and rock strength are rarely reported. This research presents a characterization method for geometric heterogeneity induced by the grain size difference. The heterogeneity of the microscopic scanning images of a coarse-grained marble is analyzed using a proposed heterogeneity index. A microstructure-based empirical model is proposed to describe the relation between the compressive strength of rock and its micro-property parameters. This microstructure-based empirical model is verified using numerical and experimental test data. The analysis results show that the proposed model can predict the strength of a granular rock better than existing models of similar nature. The model parameters for different rocks such as LdB granite, Aminadav dolomite, and Bohemian Massif granite are obtained by nonlinear regression analysis. This model is also employed to predict crack initiation and damage stresses of rocks, showing results in good agreement with the experimental data.

Formation of Pegmatitic Carbonatite in a Syenite–Marble Contact

IMMEDIATELY north of the village of Karacayir, vilayet Sivas, Turkey, a small intrusion of rather coarse-grained syenite occurs in a banded marble formation of unknown age. Here I had occasion to study in some detail a peculiar coarse-grained marble of pegmatitic appearance, containing biotite and apatite. The banded marbles seem to be regionally metamorphosed, on which the thermal metamorphism caused by the intrusion is superimposed. The part of the marble which protrudes into the syenite is changed into a carbonatite–pegmatite. Otherwise the marbles retain their regular banding, which even seems to be accentuated when nearing the contact. Within the aureole of thermal metamorphism small crystals of phlogopite and diopside develop in small amounts on the stratification planes as well as throughout the marble. Near the contact small dikes of syenite–aplite and more-or-less crushed syenite–pegmatite cut through the marbles; the syenite itself contains locally muscovite.