Chevkinite-group minerals are rare earth element (REE) carriers in alkaline magmatic and metasomatic systems, yet their hydrothermal stability and alteration pathways remain poorly constrained. We experimentally investigated the hydrothermal transformation of chevkinite (Cvk)-(Ce) under conditions relevant to alkaline rock environments, with particular emphasis on the formation and composition of secondary monazite (Mnz)-(Ce). Twenty-four cold-seal autoclave experiments were conducted at 500–600°C and 200–400 MPa for durations of 21–63 days, using natural Cvk-(Ce) from the Diamer district (Pakistan) together with quartz, albite, and variable accessory components, and reacting them with F- and Ca-bearing aqueous fluids. Mnz-(Ce) crystallized in 200 MPa in six experiments, typically as microcrystalline aggregates (<20 µm) surrounding or replacing primary Cvk. The main associated phases were britholite-(Ce) and titanite. Electron backscattered diffraction confirmed full crystallinity, while electron probe microanalysis) showed that all products are compositionally homogeneous Mnz-(Ce) with dominant phosphate components (∼97.7 wt%), minor silicate substitution (∼2.3 wt%), and no significant REE fractionation relative to the precursor Cvk. Experimental results indicate that Mnz-(Ce) formation is promoted by F- and P-rich fluids and inhibited by high Ca, Fe, and Al activities, which instead favour epidote-supergroup minerals and britholite. Systems with low Ca preferentially stabilized Mnz-(Ce) and albite. These experiments demonstrate that Mnz-(Ce) can form readily during hydrothermal alteration of Cvk -(Ce) under closed-system conditions, providing new constraints on REE mobility, mineral stability, and metasomatic processes in alkaline geological environments.
Petrological observations and major elements analyses in olivine crystals in small xenoliths (>1.5 cm in diameter) from the Jeziorna locality, SW Poland, are presented. The olivines show very large variations in the composition of Mg, Fe, Ca and Ni, which suggests the influence of many possible factors, such as (1) regional variability of the samples; (2) changes in temperature during movement and storage of Cenozoic magmas; (3) weathering; and (4) the interaction of basaltic magma with xenoliths in the mantle or during magma ascent. The latter processes are the final changes recorded in the olivine composition. This study contributes to our understanding of which of the changes in chemical composition can be attributed to these final changes, whether they occur only at the xenolith–host rock contact, or whether they also change the olivine composition inside the xenolith.
Lamprophyre Clan Rocks (LCRs) such as lamprophyres, lamproites and kimberlites are reported from many parts of the cratonic areas in India, especially the diamondiferous Eastern Dharwar Craton (EDC). Although the most common hosts of diamonds are kimberlites and lamproites, different types of lamprophyres elsewhere in the world are also reported to contain diamonds. Owing to the fact that the lamprophyres and kimberlites in the Wajrakarur Kimberlite Field (WKF) are cogengetic, this study attempts for the first time to validate the diamond potentiality of WKF lamprophyres situated at Korrakodu, Kadiri, Kalagalla, Udiripikonda, Sivarampet, Khaderpet, Lattavaram (P-8) and Mudigubba using geochemical data. The geochemical plots of selected cationic wt.% for major oxides and trace elements show that Khaderpet and Lattavaram aillikites (ultramafic lamprophyres) are diamondiferous, with plausible chances of diamond incidences in the Kadiri and Mudigubba calc-alkaline lamprophyres. The trace-element plot of Ta and Sc also shows that the Khaderpet and Lattavaram lamprophyres are diamondiferous. The geochemical data reveal that diamond grade (DG) values are inversely proportional to TiO2 content. It is also observed that the WKF lamprophyres contain some of the diamond indicator minerals. This study shows that the ultramafic lamprophyres of Khaderpet and Lattavaram, have DG values of Kadiri and Mudigubba lamprophyres showing DG values of 5.42 and 7.32 respectively and warrant detailed investigation. The higher DG values for Khaderpet (6.73) and Lattavaram (3.84) are consistent with exploration results. To date, no drilling has been conducted on the WKF lamprophyres except Khaderpet and Lattavaram; all the other lamprophyre outcrops are amenable for further exploration and drilling to ascertain their diamond potential and enhance understanding of the mantle systematics of this region.
An unusual phlogopite-amphibole-plagioclase-bearing websterite xenolith has been sampled in an alkali basaltic pyrolastite from Guinadji volcano, SE Ngaoundéré, Adamawa plateau, northern Cameroon, eastern extension of the continental sector of the Cameroon volcanic line. This olivine-free websterite exhibits cumulative texture with diopside (En43.88–45.13Wo45.90–46.91Fs8.92–9.28; Mg#: 0.83–0.85) and enstatite (En75.98–76.65Wo1.21–1.76Fs21.74–22.45; Mg#: 0.77–0.79) as cumulus phases while plagioclase, a labradorite (An58.30–An61.47), represents the intercumulus phase. Amphibole is an edenite and has a Mg# varying between 0.82 and 0.83 while phlogopite has a Mg# of 0.86. Using clinopyroxene geothermobarometer, the estimated mineral equilibration temperature ranges from 1195°C to 1208°C, at pressure between 4.7 and 5.9 kbar. The metasomatic minerals filling small spaces among these pyroxenes have high potassium (K2O ∼10 wt% for phlogopite and ∼2 wt% for amphibole), high titanium (TiO2 ∼4 wt% for phlogopite and ∼2 wt% for amphibole) and high fluorine (F > 1.20 wt%) contents. This websterite would thus be of cumulative origin, formed from tholeiitic magma and metasomatized by a K–F rich crustal-derived fluids/melts with relatively high contents of Ti. The estimated high temperature at low pressure suggests a steep geothermal gradient which could be attributed to the existing plume underneath this region. Upwelling of tholeiitic magma, which represents the parental melt of the cumulate, was emplaced at the crust–mantle boundary, where the cumulate crystallized. Continued plume upwelling subsequently led to the uplift and re-equilibration of this cumulate at depths of approximately 20 km, where it underwent metasomatic modification.
Chert, a primarily silica-bearing sedimentary rock, is often found in limited layers within the Earth's lithosphere. Optical microscopy, X-ray diffraction, major and trace element analyses were used to study chert samples from Gebel El-Khashab—an Oligocene formation consisting of fluvial sands and chert gravels together with silicified wood fragments and tree trunks in east Cairo, Egypt. The chert samples are quartz ± goethite ± moganite, with no evidence of an opal precursor. They are characterized by a variety of silica fabrics, comprising microcrystalline quartz, megaquartz, and chalcedonic quartz. The microcrystalline quartz is most common and likely formed inorganically by direct precipitation from solution. Several trace components are recognized in microcrystalline fabrics, including: (1) calcite, (2) detrital quartz and zircon, (3) echinoderms and other unidentified fossils, (4) organic textures, and (5) organic-rich structures that are potential fossil morphologies. The preservation of echinoderm fossils and organic morphologies point to primary deposition of silica. The chert samples studied here averaged 95 wt.% SiO2, 2 wt.% Fe2O3T, 0.5 wt.% CaO, 0.11 wt.% MnO, 0.1 wt.% Al2O3, 0.03 wt.% MgO, 0.02 wt.% TiO2, 0.02 wt.% K2O, and 0.03 wt.% Na2O. The low total rare earth element content (3 ppm), high Eu anomalies, low Y/Ho values and the discrimination diagrams Al–Fe–Mn, Fe/Ti–Al/(Al + Fe + Mn), and Al2O3/TiO2–Al/(Al + Fe + Mn) indicate the hydrothermal origin of silica in these cherts. The hydrothermal silica-derived cherts were deposited close to the mid-oceanic ridge, as indicated by the Al2O3/(Al2O3 + Fe2O3T) and the Fe2O3T/TiO2–Al2O3/(Al2O3 + Fe2O3T) association diagram. The chert deposits were transported in Oligocene to their current setting. The positive Ce anomalies of some chert samples point to an influence of a terrestrial material source.
This study reports the discovery of a large occurrence of magnesite metacarbonates above the northern shore of Selvågen, Prins Karls Forland (PKF), Svalbard. The stratabound magnesite occurs within the Scotiafjellet Group metasedimentary rocks of PKF and represents the first documented example of a magnesite in this region of Svalbard. The magnesite is hosted by cryptocrystalline metacarbonates containing distinctive chert bands and nodules, with associated mineral assemblages including quartz, dolomite, albite, muscovite, and pyrite. Petrographic features, such as zoned magnesite with Fe-rich rims and foliated carbonate matrices, suggest multiphase formation under greenschist facies conditions. Raman spectroscopy of carbonaceous material indicates metamorphic temperatures of 260–360°C. The magnesite likely formed through fluid-mediated metasomatism during Caledonian tectonism, with magnesium-rich fluids potentially sourced from devolatilized ultramafic complexes. This discovery enhances understanding of Svalbard’s tectonometamorphic evolution and suggests that PKF may hold broader geological and paleobiological significance, especially given the presence of organic-rich cherts containing bioclasts.
Hydromagnesite, Mg5(CO3)4(OH)2⋅4H2O, is a naturally occurring mineral belonging to the group of hydrated magnesium carbonates containing hydroxyl groups, part of the MgO–CO2–H2O system. Its formation requires high Mg/Ca ratios, typically linked to ultramafic rock weathering, and is influenced by pH, with alkaline conditions being favorable. Hydromagnesite commonly forms in alkaline lakes, as efflorescences on carbonate rocks, and even in meteorites, and plays a key role in CO2 capture and storage. This study characterizes natural hydromagnesite forming as spring efflorescences on a sandstone tor in the Stone Town Nature Reserve, Ciężkowice, Poland. The site hosts pickeringite, MgAl2(SO4)4⋅22⋅H2O, and alunogen, Al2(SO4)3∙17⋅H2O, rich efflorescences during summer, reflecting significant seasonal pH variations. This represents perhaps the first discovery of hydromagnesite on such rocks in Poland. The paper describes mineralogical and geochemical characteristics of the efflorescence and hydromagnesite itself, using methods SEM-EDS, XRPD, EPMA, Raman spectroscopy, and STA coupled with QMS for the analysis of evolved gases. Hydromagnesite crystals exhibit an acicular to flame-bladed habit, often with irregular surfaces covered by flaky and flocculent grains, clustering in aggregates. The calculated formula is Mg5(CO3)4(OH)2⋅5.14 H2O (based on five cations). Crystals of hydromagnesite are monoclinic (space group P21/c) with: a = 10.050(8) Å, b = 8.921(7) Å, c = 8.384(6) Å, β = 114.291(25)°. Raman spectra reveal intense bands at 1119 cm−1 (ν1 CO32−), weaker bands at 710, 732, 762 cm−1 (ν4 CO32−), 646 cm−1 (ν4 HCO3−), and OH-stretching vibrations at 3515, 3445, and 3373 cm−1. Thermal effects associated with hydromagnesite occur at 270°C and 390°C, corresponding to dehydration and overlapping dehydroxylation and decarbonation, respectively. The relatively low decarbonation temperature likely results from crystal morphology enhancing heat transfer and earlier CO2 release. Although the efflorescence contains minor hexahydrite, gypsum, and quartz, the above parameters for the predominant hydromagnesite are consistent with literature values.
The analysis of petrographic thin sections is a widely used process for the identification of the mineralogy of rocks and the analysis of their textural and microstructural characteristics. Despite the benefits of petrographic thin section analysis, it remains a time-consuming process with the results produced being subjective and relying on the interpretation of the researcher. In this study the benefits of integrating rotational data for petrographic thin section images in plane and cross polarised light to improve the outcomes of image analysis were investigated. This was done using image stacks representing a full 90° rotation of the thin section because the angle between the polarisation of light and the mineral orientation alters the set of observed properties for each grain. Since the range of colour values upon rotation are more indicative than a single value at one orientation these are then attributed as ranges to each pixel. Grain segmentation is performed on these images and the pixel values are extracted and attributed to their associated grain. This is done with the assistance of Micro-fabric analyser, a software developed to identify grain boundaries, and produces a data set of objects representing their associated grains along with the corresponding shape data. Using the extracted pixel values, the aim is to determine a number of optical properties such as birefringence and extinction angle (both properties that rely on orientation of the mineral grains and therefore could not be extracted without integrating rotational data). These calculated values provide more diagnostic indicators of the minerals present as well as providing microtextural data for the minerals observed. Textural data for mineral groups are extracted such as grain shape, size and orientation. To achieve this, workflows were established for the acquisition and compositing of data to optimise image analysis.
Intensive military operations took place in the southern Baltic Sea during World War II (WWII). It was also a dumping ground for munitions after the war. During storms, military artifacts are washed onto the coast. The Kołobrzeg beach is a place known for such findings. In Kołobrzeg, one of the most recognizable WWII battles between Polish-Soviet and German troops took place. Here, we report on a unique specimen found on the Kołobrzeg beach in 1996. It consists of three fused components, including conglomeratic sandstone, limestone pebble and a fragment of a worn brass gun bullet casing. Heat markings in the form of a dark halo close to the bullet fragment and black efflorescence on the surface of quartz grains suggest that the fusion was caused by heat during the explosion of gunpowder inside the bullet casing. This process led to the formation of a rock-like material resembling a well-cemented conglomerate.
This short communication proposes a novel approach to arsenate remediation using in situ precipitation of mimetite [Pb5(AsO4)3Cl], a sparingly soluble mineral phase with an apatite structure. The Pb2+ source was provided by a lead-modified zeolite (clinoptilolite) loaded with approximately 70 g Pb/kg. It was reacted with arsenate (50 mg As/L) and chloride (20 mg Cl/L) at initial pH values of 2 and 7. Mimetite crystallized on and in the vicinity of zeolite due to the reaction of Pb(II) desorbed from zeolite with arsenate and chloride ions present in aqueous solution: 5Pb2+desorbed from zeolite+3AsO43−contamination+Cl−supplied extra=Pb5AsO43 Clprecipitated5{{\text{Pb}}^{2+}}_{\text{desorbed}\ \text{from}\ \text{zeolite}}+3{{\text{AsO}_{4}^{3-}}_{\text{contamination}}}+\text{C}{{\text{l}}^{-}}_{\text{supplied}\ \text{extra}}={{\text{Pb}}_{5}}{{\left( {{\text{AsO}}_{4}} \right)}_{3}}{{\text{Cl}}_{\text{precipitated}}}
The diagenetic processes exhibited by the Neoproterozoic diamictites from Murchisonfjorden (Nordaustlandet, NE Svalbard) are presented. Diamictite samples from the Cryogene Polarisbreen Group - the Petrovbreen Member of the Elbobreen Formation and the Wilsonbreen Formation were analysed. The mineralogical associations composed of chlorite group minerals (chamosite), albite, calcite, Fe-dolomite, clay minerals (illite) and quartz, recognized by integrated optical microscopy, scanning electron microscopy (SEM) and Raman spectroscopy techniques are typical for an advanced stage of mesogenetic diagenesis. Low-grade burial mineral associations were not identified. Our investigations indicate that during diagenesis increased heat flux accompanied fluid migration and remineralization. Identified Fe-Ti – oxides, anatase in thin sections and magnetite identified by rock-magnetic experiments are the products of the secondary diagenetic mineralization. The ferromagnetic carriers representing primary depositional remanence magnetization (DRM) were not preserved.
Peridotite xenoliths from Scania (S Sweden), brought to the surface by Mesozoic basanitic magmas, provide insights into the lithospheric mantle underlying the East European Craton. During their ascent, some of the entrained xenoliths were infiltrated by a Si-undersaturated melt. The infiltration triggered orthopyroxene dissolution and the formation of fine-grained olivine, clinopyroxene and Si-rich glasses (trachytic/trachydacitic and dacitic). The latter interacted with clinopyroxene and/or spinel creating spongy rims of various thicknesses (from few to hundreds of μm). The reactions varied in intensity and effect depending on the distance from the xenolith margin and the duration of the reaction time. At the outer parts of xenoliths, intense reactions dissolved orthopyroxene entirely, forming spongy rims on spinel and clinopyroxene, while inner sections showed limited reactions, primarily between mafic melts and orthopyroxene. The local reheating and melting of fine-grained aggregates during the ascent of xenoliths resulted in the formation of a hydrous, high-Mg, glass-like phase.
Studying the properties of hard tissues, such as bones or teeth, often requires an experimental approach that enables the mechanisms observed in clinical settings to be explained or supports the safe planning of clinical trials. This paper compiles some methodological insights on the proper preparation of biogenic apatite found in human teeth for in vitro studies. These insights were gathered through experimental work and a review of some literature related to in vitro studies on the impact of metal orthodontic appliances on the chemical and crystallographic properties of dental enamel.
MinPlotX is an open-source software for mineral formula recalculation and compositional plotting providing an easy-to-use stand-alone graphical user interface (GUI) as well as an advanced programming interface (API). The aim of MinPlotX is to provide publication-ready tables of mineral formulae and plots of mineral composition. The new GUI-based approach allows for a wider variety of calculation and plotting options, including both commonly used pre-defined mineral specific diagrams and a large variety of multi-dimensional diagrams that can be created quickly and easily by the user. The most powerful feature is the addition of nearly any kind of numerical or categorized metadata, such as sample name, analysis location, trace element concentration, age, and others, that can be used to subdivide or contour data. The modular nature of the program makes it possible to add new mineral formula recalculation and plotting routines, as well as other data science tools, without changing the overall structure of the program. Therefore, MinPlotX provides advanced users the means to add new routines and interact with the program through the API, while simultaneously providing a simple and effective platform for users who have no programming experience or do not have access to MATLAB®.
This short report presents the investigation results on the zircon from meta-andesitic rock from the Ankarede Volcanite Formation of the Lower Köli Nappe Complex in Scandinavian Caledonides. Previous U-Pb dating revealed a wide span of dates ranging from ca. 520 to ca. 480 Ma, with a mean age of 491 ± 3 Ma for the zircon cores. Using cathodoluminescence and back-scattered electron imaging, along with chemical mapping, we identified distinct zones within the zircon grains; 1) cores of clear magmatic provenance, 2) mantles also of magmatic origin but with a slightly different chemical composition and 3) zircon rims that suffered metamictisation and fluid-induced alterations. These findings highlight a complex growth history and alteration of studied zircon that affect the interpretation of zircon dating results. This research underscores the importance of detailed zircon studies for understanding the intricate processes involved in the magmatic and metamorphic evolution of Virisen terrain in Scandinavian Caledonides.
This study undertook laboratory incubation approach to examine abiotic and biotic factors potentially influencing the bioweathering of Egyptian dimension stones, namely Nubian sandstone and Theban limestone. The dynamic and efficiency of metal release were assessed by means of bioleaching experiments (quantification by inductively coupled plasma mass spectrometry), whereas potential element donor phases were identified by scanning electron microscopy (SEM-EDS). Overall, biotic weathering plays more of an important role for initiation of limestone dissolution, whereas its contribution to sandstone dissolution is more specific to host minerals accommodating individual elements. Kaolinite and Fe-bearing cement minerals (ilmenite and magnetite) in sandstones were found to be particularly attractive to bacteria that enhanced Al and Fe leaching by factors up to 7.0 and 5.7, respectively. Leaching of Al and Fe from limestone was enhanced by a factor up to 13 in the presence of bacteria. Siderophore concentration in biotic incubation reached 45.2-75.5 μmol L−1 and 90.6 μmol L−1 for sandstones and limestone, respectively. Regardless of immersed solid, higher Ca and Mg leaching from calcite and dolomite under chemical instead of biotic conditions was observed indicating either preferential mineral colonization by bacteria or surface passivation by biofilm. At the end of chemical incubation, up to 34.1% of Ca and up to 27.0% of Mg were leached from sandstones, whereas leaching observed for limestone was up to 0.6% (Ca) and 16.3% (Mg). Limestone dissolution was assessed at up to 1.2% (Si). This study has implications for understanding the dissolution of dimension stone used as construction and building materials and cultural heritage objects such as monuments and ornaments.
Millimeter-sized crystals of mimetite and pyromorphite, and polymineralic mimetite-pyromorphite-vanadinite crystals occur in quartz-baryte vein within paragneisses of the Sowie Mts, SW Poland. Three morphologically different mimetite crystals and a polymineralic crystal were examined by electron probe micro-analysis (EPMA), back-scattered electrons (BSE) imaging, Raman microspectroscopy, and X-ray composition mapping. Mimetite occurs as well-developed crystals, crystals built up of sub-parallel individuals due to autoepitaxial growth, and crystals extensively etched. All of the mimetite crystals are zoned with respect to pyromorphite molecule content with sharp increase up to 23 mol% in the outermost zones. The apparent vanadinite crystal actually consists of oscillatory-zoned pyromorphite + minor vanadinite core, intermediate zones composed of pyromorphite, two mimetite zones intercalated by a band of oscillatory pyromorphite and minor vanadinite, and vanadinite mantle. EPMA data show a limited miscibility between all three minerals in the polymineralic crystal. Most analyzes cluster around 10 mol% of ternary solid solution with the maximum value of ca. 30 mol%. X-ray elemental maps reveal sharp boundaries between compositionally contrasting zones in the crystal core. In mimetite zones, the substitution of As by P does not exceed 0.43 atoms per formula unit (apfu). In the vanadinite mantle, As + P does not exceed 0.30 apfu. The distribution of Pb is uniform throughout the crystal with the highest Ca/Pb ratio of 0.03. The observed sequence of crystallization in the polymineralic crystal can be explained by the relative changes in ions concentrations at the crystal/solution interface, i.e. within the diffusion boundary layer, in accord with the models of the autocatalytic crystal growth. The authors hypothesize that kinetically driven fast growth of the polymineralic crystals resulted in precipitation of discrete mineral phases with very limited anionic substitutions.
Volcanic rocks in the Pieniny Klippen Belt (PKB) of the Western Carpathians have been the focus of geologists for over a century (e.g. Uhlig, 1890; Małkowski, 1921). Miocene volcanism is most common in the PKB. However, there are infrequent occurrences of Cretaceous volcanic rocks. Several magmatic bodies of Cretaceous age have already been described in the PKB, including basalts at Hanigovce and Biała Woda, as well as peperites at Vršatec, and Velykyi Kamenets. The magmatic body in Vršatec occurs within the Upper Cretaceous marlstones of the Lalinok Formation, the age of which was previously determined to be younger than 100 Ma (Spišiak et al., 2011). Our new U-Pb zircon dating indicates the magmatic age to be ca. 80 Ma. This new age can be used as a benchmark for the forthcoming provenance studies of the surrounding clastic rocks in the PKB and the Outer Carpathians flysch.
The lamprophyric rocks are uncommon volatile-rich melanocratic porphyritic rocks which contain only mafic phenocrysts. The felsic minerals are confined in the groundmass. They occur as dikes, sills and diatremes. The lamprophyric rocks are sometimes associated with diamond deposits. This review article discusses the ongoing debate in igneous petrology regarding the classification of lamprophyric rocks, specifically the Lamprophyre clan vs Lamprophyre facies problem. The background of this debate is rooted in conflicting interpretations of the classification of these rocks, with some researchers grouping them into a super-group called the “Lamprophyre clan” while others emphasize the distinction between the different types of these rocks (Lamprophyre facies). The aim of this study is to provide a comprehensive analysis of relevant literature and propose a more inclusive petrological classification system for lamprophyric rocks by considering the geological setting, petrography, texture, mineralogy, whole-rock geochemistry and isotopic analysis of the various kimberlites, orangeites, lamproites, para-lamproites, calc-alkaline, alkaline and ultramafic lamprophyres. Lastly, the diamond potential is also taken into account. The implications of this study are significant for the international geological community. It proposes the adoption by the IUGS TGIR of both the Lamprophyre clan (as updated by Kamvisis & Phani, 2022, i.e. genetically interrelated rocks) and Lamprophyre facies (as suggested by Mitchell, 1994, i.e. rocks that formed under volatile-rich conditions) concepts to achieve a more widespread consensus among igneous petrologists. Both terms can be correct but they represent different perspectives in the study of these exotic rocks.
The Ghansura Rhyolite Dome (GRD) is an integral part of the Bathani volcano-sedimentary sequence (BVSs), which in turn is a vital component of the Chotanagpur Granite Gneiss Complex (CGGC), eastern India. The rhyolite dome represents a shallow-level felsic magma chamber that underwent intrusion by basaltic magma during its evolution. The rocks present in the felsic dome such as basalts, rhyolites, and intermediate hybrid rocks preserve evidence of magma mixing and mingling. The objective of this contribution is to take into account, for the first time, that magma mixing processes can play an important role in the generation of calcite in magmatic rocks. The present study focuses on the mingled rocks exposed within the rhyolite dome. Previous reports have documented the existence of two distinct zones (mafic and felsic) interfacing each other in the mingled rocks of the rhyolite dome. The mafic zones dominantly consist of mineral phases such as actinolite, hornblende, biotite, plagioclase, ilmenite, calcite, and titanite. The felsic zones comprise quartz, K-feldspar, plagioclase, and biotite. When mafic magma intruded into the felsic magma chamber, interaction between the mafic and felsic magmas caused diffusion of H, Al, and K ions from the felsic to the mafic endmember. Such diffusive activities resulted in the breakdown of augite, already crystallized in the mafic magma, to form newer minerals like actinolite, hornblende, biotite, calcite, and ilmenite. The presence of ilmenite in the mingled rocks indicates the prevalence of reducing conditions during magma interaction and evolution. Breakdown of hornblende to biotite in such a reduced environmental condition led to the formation of calcite in the mingled rocks. From the results presented in this work, we are proposing that magma mixing can be a viable mechanism to form calcite in igneous rocks by magmatic processes.
