Igneous Rock Types Research Articles

Modification of the Composition of Gabbro-Basalt Raw Materials during Melting in an Oxidizing, Inert, or Reducing Atmosphere

The processes of melting of different types of igneous rock constituting gabbro-basalt raw material are examined. The role of the main rock-forming elements in the formation of these melts for the production of mineral fibers and stone-cast articles is shown. Special attention is devoted to their influence on the viscosity and crystallizability of the production melts as well as iron—the only element present in two degrees of oxidation Fe(II) and Fe(III), which can participate, correspondingly, in the processes of Mg and Al isomorphism. Information is presented on the influence of the ratio of these oxides on the crystallization processes of mineral fibers and stone-cast articles.

Exploiting LIBS to analyze selected rocks and to determine their surface hardness based on the diagnostics of laser-induced plasma

The present work introduces a detailed investigation to discriminate between some types of igneous and sedimentary rocks. The used experimental setup was a conventional single-pulse nanosecond system with a neodymium YAG laser at two excitation wavelengths, 1064 nm, and 355 nm. The laser-induced emission spectra of the rock samples were normalized to the irradiance for both utilized laser wavelengths to compensate for the different laser pulse energies used. The surface hardness values of the studied samples were spectroscopically determined via the intensity ratios of the ionic-to-atomic spectral lines of iron in the rock samples. Besides, the laser-induced plasma parameters, namely the plasma temperature and the electron density, were calculated from the obtained spectral data. It is found that the plasma temperature, in the infrared-laser case, was higher than that of the ultraviolet laser while the electron density values were the opposite. Multivariate statistical analysis of the spectroscopic data using the principal component analysis technique revealed the possibility of discrimination between different types of rocks. Furthermore, the laser-induced breakdown spectroscopy results have been validated by comparison to the results of the energy-dispersive X-ray analysis for the same samples.

TBM performance prediction model with a linear base function and adjustment factors obtained from rock cutting and indentation tests

A new TBM performance prediction model consisting of a basic penetration function and adjustment factors for different boundary conditions is presented. The basic penetration function is implemented as a linear function with an offset from zero based on Frenzel et al. (2012). Adjustment factors are used to refine the model which reflects the model architecture used by Gehring (1995). The well-established CSM model (Rostami, 1997) was used as a reference to account for tool geometry and spacing. In addition, a new approach to account for rock brittleness is presented based on the rock mechanical interpretation of Punch penetration tests (PPT). The proposed new model was developed using full scale linear rock cutting tests from 19 igneous, metamorphic, sedimentary and artificial rock types. It was validated with 36 TBM penetration tests from tunnels in the Swiss Alps (Villeneuve, 2017), Koralm tunnel and Røssåga tunnel (Wilfing, 2016). It has a strong predictive capability for a wide range of rock and rock mass parameters. The main strengths of the model are high accuracy, simplicity of the basic penetration function and the highly transparent development process that enables a clear understanding of its strengths and limitations.

Mapping the wavelength position of mineral features in hyperspectral thermal infrared data

The Wavelength Mapper is an algorithm that searches for the deepest absorption feature in each pixel of a hyperspectral image. On a per pixel basis, it extracts the wavelength position, which serves as a proxy of the mineralogy and the feature depth as a proxy for the relative abundance. This algorithm has been used with near and shortwave infrared data, but has not yet been tested on hyperspectral thermal infrared images. It is unclear what results are expected when the Wavelength Mapper algorithm is applied to hyperspectral thermal infrared data since reststrahlen features characteristically overlap in emissivity spectra. In this paper, the Wavelength Mapper is tested on a multi-flightline airborne hyperspectral TIR dataset acquired over the Yerington Batholith, Nevada. Observations were made in the 8.05–11.65 μm wavelength range to include thermal spectral features of major rock-forming minerals, and a new color ramp is created to separate quartz-rich rocks from plagioclase-rich rocks. Our results indicate that the Wavelength Mapper creates coherent spatial patterns across flightlines. The results displayed represent different types of igneous and sedimentary rocks, as well as the products of hydrothermal alteration via different colors, mainly based on the relative abundance of quartz, feldspar and garnet, as well as mica and epidote. Comparison with published maps indicate that the Wavelength Mapper represents for each pixel a parameter value that can be linked to the spectrally dominate rock-forming mineral of that area, as mapped with traditional fieldwork methods. In conclusion, the Wavelength Mapper can be applied to airborne hyperspectral TIR data to achieve a simple, repeatable, per-pixel overview map of the dominating rock-forming mineral occurrences.

2.8 Ga Subduction-related magmatism in the Youanmi Terrane and a revised geodynamic model for the Yilgarn Craton

New studies in the central and southern parts of the Murchison Domain in the Youanmi Terrane, western Yilgarn Craton, reveal previously unidentified igneous rock types in addition to boninitic occurrences similar to those found in the northern part of the domain. New results also allow for a re-assessment of a volcanic suite previously described as examples of a “Karasjok type” of komatiite. The rocks are most plausibly examples of arc picrites, specifically of the type found in ophiolite settings. In addition to boninitic rocks and picrites, this study identified remobilized olivine-cumulate rich lavas that resemble examples found in the Troodos and Othris ophiolites. Examples of REE enriched high magnesium andesites exhibit pronounced high field strength element depletions on normalized plots combined with mantle-like Nb/Zr ratios. The rocks chemically resemble Phanerozoic examples of enriched boninites and their signatures are distinct from those typically attributed to crustal contamination of mantle plume magmas. Intrusions of the ∼2792 Ma Warriedar Suite have compositions analogous to those of post-Archean Alaskan Intrusive complexes and were likely derived from subduction-modified sub-cratonic mantle. The new observations can be accounted for in a geodynamic scenario involving subduction along the western Yilgarn margin at ∼2800 Ma. Similarities with the contemporaneous Superior Province raise the possibility that the nuclei of the two cratons were closely associated at this time.

Petrological and Mineralogical Aspects of Epithermal Low-Sulfidation Au- and Porphyry Cu-Style Mineralization, Navilawa Caldera, Fiji

The Navilawa caldera is the remnant of a shoshonitic volcano on Viti Levu, Fiji, and sits adjacent to the low-sulfidation Tuvatu epithermal Au–Te deposit. The caldera occurs along the Viti Levu lineament, approximately 50 km SW of the Tavua caldera, which hosts the giant low-sulfidation Emperor epithermal Au–Te deposit. Both calderas host alkaline rocks of nearly identical age (~5.4–4.6 Ma) and mineralization that occurred in multiple stages. The gold mineralization in these locations is spatially and genetically related to monzonite intrusions and low-grade porphyry Cu-style mineralization. Potassic, propylitic, phyllic, and argillic alteration extends from the Tuvatu Au–Te deposit towards the central, northern, and eastern parts of the Navilawa caldera where it is spatially associated with low-grade porphyry Cu–Au mineralization at the Kingston prospect and various epithermal Au–(Te) vein systems, including the Banana Creek and Tuvatu North prospects. Chalcopyrite, and minor bornite, occurs in quartz–calcite–(adularia) veins in the Kingston deposit associated with weak propylitic and phyllic alteration, whereas NE-trending epithermal gold veins at the Banana Creek and Tuvatu North prospects are associated with weak potassic alteration that is overprinted by propylitic and phyllic alteration. Gold is accompanied by chalcopyrite, galena, and sphalerite in quartz–pyrite veins that also have a Ag–As–Hg–Te signature. The temperature range for phyllosilicates in the phyllic alteration (chlorite ± smectite ± corrensite ± illite) is in good agreement with temperatures recorded from previous fluid inclusion studies of quartz at the Banana Creek Au prospect (~260 °C) and the nearby Tuvatu Au–Te deposit (205 to 382 °C). Sulfur isotope compositions of pyrite (−6.2 to +0.4‰) from the Banana Creek prospect indicate a likely magmatic source of sulfur. Oxidation of the ore fluids or a direct addition of volatiles to the hydrothermal fluids may account for the lighter isotopic values. The similarities of the igneous rock types and compositions, transition from porphyry- to epithermal-style mineralization, alteration assemblages, paragenetic relationships, and stable isotope data suggest a common origin for the porphyry- and epithermal-style mineralization within the Navilawa and between the Navilawa and Tavua calderas.

Character and tectonic setting of plutonic rocks in the Gällivare area, northern Norrbotten, Sweden

ABSTRACTPetrographical and lithogeochemical investigations in combination with mapping in the Gällivare area, northern Norrbotten, Sweden, have led to the identification of several igneous intrusive rock types. These include: (1) ultramafic-mafic complexes, (2) mafic-intermediate rocks, (3) dolerites and (4) felsic plutons. The ultramafic-mafic rocks include the ca. 1.88 Ga Dundret complex and ca. 1.80 Ga Vassaravaara complex. The Dundret complex has tholeiitic to calc-alkaline affinity, shows a primitive mineral content and was formed in an extensional tectonic setting. The Vassaravaara complex has a similar chemical signature as the Dundret complex. The mafic-intermediate plutons vary in composition from gabbro to diorite. The chemical signature of the dioritic rocks indicate formation in a volcanic arc setting. Dolerites occur as solitary dikes and have calc-alkaline affinity. The felsic plutons include granite and syenite of ca. 1.88, 1.80 and 1.78 Ga age. The felsic plutons have calc-alkaline to shoshonitic affinity and mostly show a metaluminous I-type character. Results indicate subduction at 1.90 Ga resulting in a volcanic arc system, and including extensional events generating back-arc environments leading to mafic, intermediate and felsic magmatism in the Gällivare area. Subduction at 1.80 Ga is suggested to have caused a similar process generating mafic and felsic magmatic rocks in the same area. A subsequent collision event finally generated 1.78 Ga granitic rocks.

Rare earth element geochemistry during weathering of S‐type granites from dry to humid climates of Brazil

AbstractS‐type granites are igneous rock types that are widespread in all continental crust. These granites play a key role in global weathering patterns and can be important economic ores of rare earth elements (REEs). This study provides insights into the geochemical and mineralogical signatures of REEs in S‐type granites and their derived soil profiles along a climosequence from dry to humid climates of Brazil. Mineralogical, petrographic, geochemical and soil analyses (physical and chemical) were used to evaluate the geochemistry of REEs in rock and soil samples. The granites were characterized as strongly peraluminous, being classified as typical S‐types. Both the granites and their derived soils contained high contents of REEs, with monazite and apatite being the major source of REEs. The high enrichment of light REEs (LRREs) in monazite and apatite explained the REE fractionation evidenced in the S‐type granites. The normalized REE distribution patterns for soil profiles along the climosequence revealed the fractionation between light and heavy REEs (HREEs). The ratio of La/YbN > 1 also confirmed the LREEs/HREEs fractionation. The mineralogical composition of the parent material and the clay minerals (kaolintes) seemed to govern the fractionation between LREEs and HREEs in these soils. Chemical index of alteration (CIA) values, REE fractionation and kaolinite proportions in soil profiles increased from dry to humid climates. These results suggest that the degree of weathering plays an important role in the type and volume of secondary minerals, as well as the REE fractionation. Among the phyllosilicates, kaolinite seems to be the most important adsorbent of light REE. The higher positive Eu anomalies with advanced weathering are explained by the breakdown of plagioclase. The weathering of monazite and apatite was the main reason for the slight negative Ce anomalies in the soil profiles. This study can be used to comprehend the geochemistry of REEs in other parts of the tropics underlain by S‐type granites.

Mineralogical thallium geochemistry and isotope variations from igneous, metamorphic, and metasomatic systems

This study presents new thallium (Tl) concentration and isotopic composition data for potassium feldspar (K-feldspar), micas, sulfides, and other minerals using solution multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS). The samples studied represent a diverse set of igneous, metamorphic, and metasomatic rock types. Purified separates of minerals anticipated to be Tl-bearing were analyzed; in many cases coexisting minerals were measured to examine the distribution of Tl and its isotopes between coexisting phases. This study is the first of its kind to document mineralogical controls on Tl chemical and isotopic fractionation.Thallium contents in rock-forming minerals and common sulfides vary from below detection limit (here, approximately 0.2 ppm Tl in the mineral utilizing an IsoProbe MC-ICP-MS) to 3200 ppm. In this present study, mica and feldspar samples can reach Tl concentrations well over 20 ppm, compared to only 0.7 ppm in average crust. In contrast, only 14 of 38 common sulfide samples contain Tl at levels above the detection limit. Measured Tl isotope ratios, reported as ε205Tl relative to the NIST 997 standard solution, range from −12.1 ± 0.6 to +18.0 ±1.4 (2σ). Most samples analyzed fall within the published range of ε205Tl (−20 to +15) (Nielsen et al., 2017). Although most sulfides show limited Tl enrichment, they display the highest ε205Tl values among coexisting minerals, with Fe-rich micas having the lowest ε205Tl values.The patterns in enrichment are best interpreted to reflect crystal chemical differences and the incompatible, dominantly lithophile nature of Tl. In turn, isotopic fractionation also reflects control by the bonding environment as well as redox conditions. The preferential distribution of Tl into micas and K-feldspar found here is consistent with the similarity in charge and ionic radius of Tl+ and K+. The higher ε205Tl values in sulfides agree with previous observations and theoretical studies showing the tendency of covalent bonds, high bond strengths, and high oxidation states to favor heavy isotopes. This work highlights important areas for future research regarding the natural weathering of Tl-bearing substrates, understanding regional cycling of Tl, and potential bioremediation of Tl contamination.

Roman Millstones of Carthage (Tunisia): a Geoarchaeological Study Using Petrological and Geochemical Methods

A great number of Roman millstones have been discovered in the archaeological site of Byrsa at Carthage since the nineteenth century by different international archaeological teams which have excavated the site. Most of these millstones (catilli/metae) are hourglass-shaped, and all are made of igneous rocks whose source was identified through petrochemical study. The location of the artefact rock source was determined by comparing thin sections of samples taken from black and red-brownish lava catilli found at the Byrsa Roman site with geological samples taken from Tunisian volcanic rocks located in the northern-western part of the country (Nefza and Mogods regions). The comparison shows that the volcanic petrological and geochemical compositions (basalt and rhyolitic ignimbrite) of the catilli are not from local sources where basaltic and rhyodacite outcrops have been identified in the Guelb Saad Moun (Mogods region) and in the Nefza region respectively. The comparison with existing literature data on similar rocks from Italy has constrained the volcanic origin of the exploited lavas. Thus, the diversity of volcanic rocks (basalt and rhyolitic ignimbrite) suggests several outside origins, such as the Pantelleria Island for the black lava mills and Sardinia (in the area of Mulargia) for the red-brownish lava mills, where these two types of igneous rocks have been widely identified.

Shear rheology and microstructure of mining material-bitumen composites as filler replacement in asphalt mastics

Magnetite is a mineral that occurs in many types of igneous rock and can be found in large quantities in fluvial and marine environments. It can also be extracted by reprocessing of existing mine tailings. In this paper, magnetite supplied from two different mining sites was evaluated as a substitution of natural limestone filler in asphalt mix design. Magnetite and limestone fillers were added to the bitumen according to three filler/bitumen ratios to form composite asphalt mastics.Rheology of the mixes was analysed to study the effects of magnetite as potential filler in asphalt pavement applications and comparisons were made with natural limestone filler-based mastics. In addition, particle size analysis, scanning electron microscope, Cryo-SEM and energy dispersive X-ray spectroscopy, were conducted to comprehensively characterize the composite mixes.Results showed that the addition of magnetite-based ferromagnetic filler in asphalt mix design represents a suitable way to recycle this material, which is available in large quantities in many countries. In addition, ferromagnetic particles could also be exploited for induction or microwave healing of asphalt cracks as demonstrated by recent studies.Viscoelastic properties of the bituminous mastic are improved by reducing the mastic’s temperature and loading time susceptibility; stiffness and elastic behaviour at high temperature was also improved hence potentially increasing resistance to permanent deformation.

Provenance of the Gondwana sediments, Palar Basin, Southern India

Palar Basin is considered as one of the pericratonic rift basins of East Coast of India. An integrated petrography, clay mineralogy, and heavy mineral studies of sandstone and shale from the Palar Basin South India, Tamil Nadu, have been carried out to decipher their provenance, palaeoclimate, and tectonic setting. The mineralogical make-up of the clastic rocks is largely composed of quartz followed by feldspar, rock fragments with minor amounts of chlorite, glauconite, zircon, garnet, and opaque. Palar sandstones are coarse to medium-grained and mineralogically immature (poorly sorted and few are moderately sorted). The detrital quartz grains consist of well rounded and rounded quartz, monocrystalline quartz with uniform or straight extinction, and polycrystalline grains with five crystals of straight to slightly curved intercrystalline boundaries. Few of the monocrystalline quartz contain inclusions of sillimanite, rutile, and zircon needles and low content of plagioclase and k-feldspar. These petrographic analyses of the sandstone suggest derivation from metamorphic, igneous, and reworked sediments of different grades which infer that the recycling and the clasts were subjected to both long and short transport distances. The recycled orogen provenance suggests that the sandstone has been derived predominantly from low-lying granite and gneissic sources. The framework petrography exhibits (a) higher percentage of quartz, (b) predominance of monocrystalline grains, (c) feldspar affinity, and (d) paucity of rock fragments, and low F/R ratio suggests that the sediments deposited were in a passive continental margin tectonic setting. The presence of euhedral, angular, and subrounded grains of zircon, rutile with reddish and dark boundaries, the high and moderate ZTR Index (zircon-tourmaline-rutile) and the ratio of RuZi (rutile/zircon) and GZi (garnet/zircon) low values reveal that the Palar Basin sediments were sourced from the combination of metamorphic and igneous (granite and gneisses) rock types. The presence of high amount of rock derived clay (illite, chlorite) is predominant than soil derived (kaolinite, smectite) clay minerals. The high content of illite indicates the source of the clay minerals from pre-existing rocks of granite and gneisses, subjected to physical weathering over chemical weathering in a temperate climate (hot/humid) with moderate hydrolysis.

Provenance discrimination between Atasta and Alvarado beach sands, western Gulf of Mexico, Mexico: Constraints from detrital zircon chemistry and U–Pb geochronology

The bulk sand samples and detrital zircons collected from the Atasta and Alvarado beach areas in the southwestern Gulf of Mexico have been analysed for geochemistry and U–Pb ages to constrain their provenance. The index of chemical maturity and SiO2/Al2O3 ratio of the Atasta and Alvarado beach sands indicated low compositional maturity. The chondrite‐normalized REE patterns and Eu anomalies of the Atasta and Alvarado beach sands suggested that the sands were derived from felsic and intermediate igneous rock types, respectively. A wide range in Th and U contents of the Atasta (~1.0–884 ppm and ~39–883 ppm, respectively) and Alvarado (~13–2,641 ppm and ~21–2,457 ppm, respectively) zircons likely indicates that the detrital zircon populations consist of zircons derived from multiple sources. The total rare earth element (ΣREE) content in the Atasta and Alvarado zircons ranges from ~151 to 2,088 ppm and ~154 to 3,580 ppm, respectively. The chondrite‐normalized REE patterns of zircons from the two beach areas show slightly depleted light REE (LREE) and enriched heavy REE (HREE), as well as positive Ce and negative Eu anomalies. A few zircons of Alvarado beach lack a Ce positive anomaly but exhibit a distinct Eu anomaly. The differences in REE patterns among zircons between the two beach areas revealed the variations in the type of source terranes, which supplied zircons to the beach areas. The detrital zircon age distribution for the Atasta beach is homogeneous, showing a prominent Proterozoic peak (~596–2,461 Ma; number of samples n = 62) with few Cenozoic (~10.43–65.2 Ma; n = 4) and Palaeozoic (~380–468 Ma; n = 5) zircons. The zircon U–Pb ages of Alvarado beach revealed Cenozoic (~0.25–63.9 Ma; n = 65), Mesozoic (~67.9–181.2 Ma), Palaeozoic (~252–297 Ma), and Proterozoic (~589–1,501 Ma) age clusters with predominant Cenozoic zircons. The comparison of zircon REE chemistry and geochronological data of this study with published data suggests that the source terranes, which supplied zircons to the Atasta beach, were the Chiapas Massif and Oaxacan complexes, whereas the zircons in the Alvarado beach were derived from the nearby Mexican Volcanic Belt and Eastern Alkaline Province. The provenance variation between the two beach areas was also revealed by the dissimilarities in zircon age clusters.

Insights into the evolution of an alkaline magmatic system: An in situ trace element study of clinopyroxenes from the Ditrău Alkaline Massif, Romania

Clinopyroxene is a major constituent in most igneous rock types (hornblendite, diorite, syenite, nepheline syenite, camptonite, tinguaite and ijolite) of the Ditrău Alkaline Massif, Eastern Carpathians, Romania. Phenocryst and antecryst populations have been distinguished based on mineral zoning patterns and geochemical characteristics. Major and trace element compositions of clinopyroxenes reflect three dominant pyroxene types including primitive high-Cr Fe-diopside, intermediate Na-diopside-hedenbergite and evolved high-Zr aegirine-augite. Clinopyroxenes record two major magma sources as well as distinct magma evolution trends. The primitive diopside population is derived from an early camptonitic magma related to basanitic parental melts, whilst the intermediate diopside-hedenbergite crystals represent a Na-, Nb- and Zr-rich magma source recognised for the first time in the Ditrău magmatic system. This magma fractionated towards ijolitic and later phonolitic compositions. Field observations, petrography and clinopyroxene-melt equilibrium calculations reveal magma recharge and mingling, pyroxene recycling, fractional crystallisation and accumulation. Repeated recharge events of the two principal magmas resulted in multiple interactions between more primitive and more fractionated co-existing magma batches. Magma mingling occurred between mafic and felsic magmas by injection of ijolitic magma into fissures (dykes) containing phonolitic (tinguaite) magma. This study shows that antecryst recycling, also described for the first time in Ditrău, is a significant process during magma recharge and demonstrates that incorporated crystals can crucially affect the host magma composition and so whole-rock chemical data should be interpreted with great care.

Evaluation of Accelerated Ageing Tests for Metallic and Non-Metallic Graffiti Paints Applied to Stone

Graffiti are increasingly observed on urban and peri-urban buildings and their removal requires a huge financial outlay by local governments and agencies. Graffiti are not usually removed immediately, but rather over the passage of time, viz. months or even years. In this study, which forms part of a wider research project on graffiti removal, different methods (gravimetric analysis, examination of digital images, colour and infrared measurements) were used to evaluate the performance of accelerated ageing tests (involving exposure to humidity, freeze-thawing cycles and NaCl and Na2SO4 salts) for graffiti painted on stone. Silver (metallic) and black (non-metallic) graffiti spray paints were applied to two types of igneous rock (granite and rhyolitic ignimbrite) and one sedimentary rock (fossiliferous limestone, i.e., biocalcarenite). The metallic and non-metallic graffiti spray paints acted differently on the stone surfaces, both chemically and physically. Older graffiti were found to be more vulnerable to weathering agents. The ageing test with NaCl and particularly Na2SO4, both applied to granite, proved the most severe on the paints, yielding more detrimental and faster artificial ageing of the type of material under study.

Model to Assess the Quality of Magmatic Rocks for Reliable and Sustainable Constructions

Geomechanical assessment of rocks requires knowledge of phenomena that occur under the influence of internal and external factors at a macroscopic or microscopic scale, when rocks are submitted to different actions. To elucidate the quantitative and qualitative geomechanical behavior of rocks, knowing their geological and physical–mechanical characteristics becomes an imperative. Mineralogical, petrographical and chemical analyses provided an opportunity to identify 15 types of igneous rocks (gabbro, diabases, granites, diorites, rhyolites, andesites, and basalts), divided into plutonic and volcanic rocks. In turn, these have been grouped into acidic, neutral (intermediate) and basic magmatites. A new ranking method is proposed, based on considering the rock characteristics as indicators of quantitative assessment, and the grading system, by given points, allowing the rocks framing in admissibility classes. The paper is structured into two parts, experimental and interpretation of experimental data, showing the methodology to assess the quality of igneous rocks analyzed, and the results of theoretical and experimental research carried out on the analyzed rock types. The proposed method constitutes an appropriate instrument for assessment and verification of the requirements regarding the quality of rocks used for sustainable construction.

Klasifikasi Batuan Beku Gabbro Pada Citra Sayatan Tipis Menggunakan Multilevel Otsu’s Thresholding

Citra sayatan tipis batuan merupakan metode pengaman yang digunakan untuk menentukan jenis batuan dan nama dari batuan berdasar pada mineral penyusun. Melakukan pengamatan sayatan tipis sulit dilakukan jika hanya menggunakan bantuan mikroskop polarisasi karena kemampuan mata manusia tidak dapat melakukan identifikasi secara mendetail. Oleh karena itu analisis dan identifikasi mineral menjadi lebih mudah dilakukan dengan bantuan pengolahan citra digital dengan menggunakan algoritma Multilevel Otsu’s Thresholding untuk mengetahui kelimpahan mineral batuan beku. Data yang digunakan dalam penelitian ini menggunakan citra sayatan tipis batuan beku yang diakuisisi dari penggunaan mikroskop polarisasi dengan perbesaran 10x. preprocessing yang dilakukan dengan 2 perlakuan yang berbeda yaitu garyscale dan grayscale dengan k-means untuk mengetahui hasil yang maksimal. Selanjutnya tahap pengolahan dilakukan segmentasi Multilevel Otsu’s Thresholding dengan dua nilai ambang. Selanjutnya analisis pada hasil segmentasi untuk mengetahui kelimpahan mineral. Hasil perhitungan dan analisis yang telah dilakukan pada preprocessing yang menggunakan grayscale dan grayscale dengan k-means yang kemudian di lakukan segmentasi Multilevel Otsu’s Thresholding memiliki akurasi paling tinggi 40% dan 33,57%. Dari kedua perlakuan dapat disimpulkan bahwa penggunaan k-means pada preprocessing memiliki pengaruh pada pengolahan citra sayatan tipis batuan beku jenis gabbro dengan nilai akurasi tertinggi dari dua perlakuan yaitu 40% dengan menggunakan preprocessing k-means dengan nilai k=7.

Reference data set of volcanic ash physicochemical and optical properties

AbstractUncertainty in the physicochemical and optical properties of volcanic ash particles creates errors in the detection and modeling of volcanic ash clouds and in quantification of their potential impacts. In this study, we provide a data set that describes the physicochemical and optical properties of a representative selection of volcanic ash samples from nine different volcanic eruptions covering a wide range of silica contents (50–80 wt % SiO2). We measured and calculated parameters describing the physical (size distribution, complex shape, and dense‐rock equivalent mass density), chemical (bulk and surface composition), and optical (complex refractive index from ultraviolet to near‐infrared wavelengths) properties of the volcanic ash and classified the samples according to their SiO2 and total alkali contents into the common igneous rock types basalt to rhyolite. We found that the mass density ranges between ρ = 2.49 and 2.98 g/cm3 for rhyolitic to basaltic ash types and that the particle shape varies with changing particle size (d < 100 μm). The complex refractive indices in the wavelength range between λ = 300 nm and 1500 nm depend systematically on the composition of the samples. The real part values vary from n = 1.38 to 1.66 depending on ash type and wavelength and the imaginary part values from k = 0.00027 to 0.00268. We place our results into the context of existing data and thus provide a comprehensive data set that can be used for future and historic eruptions, when only basic information about the magma type producing the ash is known.

Caldera of Godean, Sleman, Yogyakarta: A Volcanic Geomorphology Review

Godean hills is located approximately 10 km westward from the Yogyakarta City. The landscape of Godean hills and plains is affected by various factors, such as lithology, geological structure, and sub-aerial process. The purpose of this study was to reveal the landscape of Godean. The method consisted of field study, morphological variables assessment, rock sampling, and laboratory analysis. The results of field mapping indicated that the landscape of Godean is an isolated hill with a steep slope of >40° and an elevation of +231 m a.s.l, passed by the rivers flows from northeast to southwest that disembogue into the west part of Kulon Progo. The morphologhy of Godean hills varies including G. (Gunung/Mountain) So (+173 m amsl), G. Gede (+218 m a.s.l), G. Wungkal (+187 m a.s.l), G. Butak (+154 m a.s.l), and G. Berjo ( + 175 m a.s.l), dominated by the lithology of igneous rock, which is composed of porphyry andesite-microdiorite, pumice lapilli, and quartz rich lapilli-tuff. In addition, most of the igneous rocks have weathered and have been altered to clays, while the deposition from Merapi volcano formed a landscape with an altitude between +100–+150 m a.s.l surrounding Godean hills. Sentolo Formation was found in Kembang, Bantul, which is located approximately ±5km in the south of the study area N93ºE/12º, while the distribution in the southwest and northeast relatively covers the Godean hills in curve shape. The results of the analysis provide information related with Godean landscape that it is the remains of the volcanic caldera, with various igneous rock types and volcaniclastics deposits, as well as endured the occurrences of hydrothermal alteration and mineralization. Further geophysical research is required to determine the configuration of igneous rocks under the earth's surface.

Analysis of bead wear in diamond wire sawing considering the rock properties and production rate

Predicting the wear rate of diamond beads in the diamond wire sawing process is one of the most important factors in the optimized design and cost estimation of quarrying. This paper aims to predict the wear rate of diamond beads as one of the principal performance criteria in dimension stone quarrying. Saw operating parameters and mechanical and physical properties of rock are the most effective factors on diamond bead wear. In the same working conditions (at constant operating parameters), the wear rate of diamond wire saw is strongly affected by the production rate, and the characteristics of rock. In this study, the uniaxial compressive strength, Schmiazek abrasivity factor, Mohs hardness, and Young’s modulus were selected as the main physical and mechanical properties of rock. The 11 types of igneous rocks were cut in the laboratory using a diamond wire saw and a fully instrumented cutting platform. During the cutting process, the wear rate of diamond beads were determined after each cutting test. The wear rate of diamond bead and rock characteristics were evaluated using simple and multiple curvilinear regression analysis, and prediction models were developed. The developed models were validated by considering the t-test, F-test, correlation coefficient and the plots of predicted versus actual values. The results indicated that the wear rate of diamond beads can be reliably predicted using the developed model.