Hematite Inclusions Research Articles

A new occurrence of lazulite from the Main Central Thrust in Kumaun Himalaya, India: fluid inclusion, EPMA and Raman spectroscopy focusing on lazulite in a highly tectonized zone

Abstract The present study reports and investigates ‘lazulite’ occurring in the vicinity of a highly tectonized zone of the Main Central Thrust (MCT) in the Himalaya. The azure blue lazulite, hosted in quartz veins, occurs in fractured Berinag quartzite, which forms the footwall of the MCT near Sobla village in NE Kumaun Himalaya, India. Lazulite was investigated using SEM-EDX, micro Raman spectroscopy, fluid inclusion microthermometry and electron probe microanalysis (EPMA). Lazulite contains inclusions of rutile and hematite and has Mg/(Mg+Fe) ratios of 0.86 to 0.90. The phosphorus in lazulite shows a negative trend with Mg+Al contents. This lazulite is an intermediate solid solution near the lazulite end-member with a cationic composition in the structural formula: Mg 0.81–0.89 Fe 0.10–0.13 Al 1.88–1.98 P 2.00–2.07 . Its composition in the lazulite–scorzalite stability field points to a higher temperature of its formation. Fluids trapped as inclusions in lazulite and the associated quartz are generally C–O–H fluid. The fluid inclusion isochors for lazulite, together with the temperature calculated for metamorphism of the equivalent structural level in the adjacent area suggest 500–600°C and 7.25 to 9.25 kbar, which match the peak metamorphic temperature–pressure derived elsewhere for the Higher Himalayan Crystallines. Moderately enriched δ D‰ values and H 2 O–CO 2 –low NaCl fluid suggest that water from a deep reservoir, more likely a metamorphic fluid, participated in lazulite formation. Classic sigmoidal fluid inclusions in lazulite reveal their development during MCT shearing, whereas the overpressured fluid inclusions suggest a post-lazulite uplift. The MCT lazulite is interpreted to have formed during Himalayan shearing and concurrent metamorphism. The present study also implies that this refractory mineral can sustain fluid inclusions within it against intense deformation conditions, such as in the MCT.

Mineral composition and gemological characteristics of jewelry-ornamental ammonites of the Republic of Adygea

For the first time, data on the mineral composition and gemological characteristics of the jewelry-ornamental ammonites of the Republic of Adygea have been presented. Ammonites consist mainly of the calcite with inclusions of quartz, glauconite, kaolinite, aragonite, pyrite, apatite and hematite. The walls and partitions of the shells mainly lost the original aragonite composition and consist of calcite with inclusions of pyrite and apatite. Aragonite is preserved fragmentary in the walls and partitions of the shells. Calcite contains some elements-admixture, which average volumes, (wt. %), are: Mg0,62, Mn0,31 and Fe 1,26. The color and transparency of calcite is determined by the structural features of the crystals and mineral inclusions. Ammonites of the Republic of Adygea have a wide range of sizes and are associated with sediments of the lower Cretaceous. According to the decorative and technological characteristics ammonites can be used as a jewelry-ornamental material for the production of a wide range of ware.

Tiny particles building huge ore deposits – Particle-based crystallisation in banded iron formation-hosted iron ore deposits (Hamersley Province, Australia)

The world’s major source of iron ore is hosted in Precambrian banded iron formations. These chemical (meta-) sedimentary rocks are composed of alternating laminae of iron oxide minerals and chert. Despite the economic significance of high-grade iron ore deposits, controversy persists after decades of research on how banded iron formations became upgraded to form iron ore. The fundamental requirement for iron ore formation is the removal of vast amounts of chert coupled with an increased concentration of iron oxide minerals.Here, we assess the fate of colloidal hematite inclusions encapsulated in chert after quartz dissolution and examine their role in the formation of hematite ore. We have analysed hematite ores from the Hamersley Province (Australia) using a combination of petrography, high-resolution electron microscopy and X-ray diffraction. These techniques reveal the presence of abundant nano and microscale hematite particles that we suggest form the building blocks of larger hematite crystals within the iron ore. Our textural observations indicate that hematite colloids that were previously encapsulated inside the microcrystalline quartz grains in chert layers are released during quartz dissolution, and subsequently reassemble in a self-similar fashion to from new microplaty hematite crystals via non-classical crystallisation pathways. Progressive growth and fusion leads to the transformation of hematite microplates into hematite bands, which resemble pre-existing iron oxide laminae of banded iron formations. In contrast to previous models, we observe the direct transformation of banded iron formations to microplaty hematite and have not found evidence that significant amounts of hematite formed through metamorphism of goethite or that intermediate carbonate minerals were involved during the upgrading of banded iron formations to pure hematite ore.Given the strong evidence for hypogene fluids found in many deposits, we have also assessed the role that such warm, highly saline fluids may have played during the evolution of iron ore. Using insights from crystal chemistry we conclude that fluid infiltration impacts many aspects of iron ore formation by controlling hematite colloid liberation and aggregation, and finally controlling the transformation of the colloids into macroscopic crystals of hematite via non-classical crystallisation mechanisms. Our study underlines the significance of hypogene fluids in the upgrading of banded iron formation to iron ore, however, we suggest that their influence was mainly passive as hematite was not precipitated directly from these fluids.

Memory effect and magnetocrystalline anisotropy impact on the surface magnetic domains of magnetite(001)

The structure of magnetic domains, i.e. regions of uniform magnetization separated by domain walls, depends on the balance of competing interactions present in ferromagnetic (or ferrimagnetic) materials. When these interactions change then domain configurations also change as a result. Magnetite provides a good test bench to study these effects, as its magnetocrystalline anisotropy varies significantly with temperature. Using spin-polarized electron microscopy to map the micromagnetic domain structure in the (001) surface of a macroscopic magnetite crystal (~1 cm size) shows complex domain patterns with characteristic length-scales in the micrometer range and highly temperature dependent domain geometries. Although heating above the Curie temperature erases the domain patterns completely, cooling down reproduces domain patterns not only in terms of general characteristics: instead, complex microscopic domain geometries are reproduced in almost perfect fidelity between heating cycles. A possible explanation of the origin of the high-fidelity reproducibility is suggested to be a combination of the presence of hematite inclusions that lock bulk domains, together with the strong effect of the first order magnetocrystalline anisotropy which competes with the shape anisotropy to give rise to the observed complex patterns.

Stratiform siderites from the Mesoproterozoic Xiamaling Formation in North China: Genesis and environmental implications

Stratiform or layered siderites are much less common than siderite concretions in the stratigraphic record. In the middle part of the Mesoproterozoic Xiamaling Formation (ca. 1.40–1.35Ga), layered siderites are widespread across the North China Platform. Facies analysis indicates that the Xiamaling siderites were formed in shallow-water environments above the storm wave base. High Fe/Al and V/Al ratios and the lack of pyrites in siderite-bearing strata indicate ferruginous bottom-water conditions during the formation of siderites. The low thermal maturity of organic matter and clay mineral structures suggest that the layered siderites were formed at burial temperatures ≤90°C. The negative δ13C values (−24‰ to −12‰) of siderites and the presence of μm-scale hematite inclusions in siderite grains suggest that dissimilatory iron reduction (DIR) during early diagenesis has played critical roles in siderite formation. The source of Fe-oxyhydroxides required for DIR could be from Fe(II) oxidation in shallow seawater above the redoxcline in response to enhanced hydrothermal activities or, alternatively, directly from continental Fe-oxide input. The positive cerium (Ce) and europium (Eu) anomalies of clay minerals in siderite-bearing strata and their positive correlation with total Fe contents (TFe2O3) seem to favor a hydrothermal origin of iron. Syndepositional hyalophane concretions, intermittent tuff layers, and remarkable enrichment of Cu and Zn in some of the siderite-hosting rocks provide further support to hydrothermally sourced iron. The enhanced hydrothermal activity for the development of stratiform siderites in the Xiamaling Formation probably related to the final breakup of the North China Craton from the Columbia supercontinent, during which active hydrothermal systems provided sufficient Fe(II) for Fe-redox recycling and formation of layered siderites.

Iron (oxy)hydroxide and hematite micro- to nano-inclusions in diagenetic dolomite from a 2.4 Ga banded iron formation (Minas Gerais, Brazil)

The low-grade carbonate banded iron formation of the Aguas Claras mine, from the transition of the Caue to the Gandarela Formation (2.4 Ga, Itabira Group, Brazil), is composed of porous and microsparitic dolomite, quartz, iron oxides and (oxy)hydroxides. Iron oxides occur as bands, veins and as inclusions in the dolomite crystals, whereas iron (oxy)hydroxides only occur as inclusions. Combined mineralogical analyses (X-ray diffraction, Raman spectroscopy, focused-ion-beam thinning and transmission electron microscopy) identified the inclusions in porous dolomite as hematite and minor goethite and/or ferrihydrite, whereas microsparitic dolomite only hosts hematite. Curie balance analysis on whole rock reveals that, at temperatures between ~680 °C and ~900 °C, hematite and iron (oxy)hydroxide inclusions react with the surrounding dolomite resulting in the assemblage: magnesioferrite (MgFe 2 O 4 ), srebrodolskite (Ca 2 Fe 2 O 5 ), lime (CaO), portlandite (Ca(OH) 2 ) and periclase (MgO), whereas hematite and pure dolomite do so only at ~900 °C. This difference is an indirect argument for the presence of iron hydroxide inclusions within the dolomite. The inclusions are either single crystals or form clusters in pores. The fast-Fourier-transform diffraction pattern of one single crystal can be indexed as goethite and ferrihydrite. This finding suggests an incipient solid-state transformation of ferrihydrite to goethite rather than a dissolution-precipitation process. It is suggested that the clustered hematite and the goethite/ferrihydrite precipitated from Fe- and Si-bearing fluid inclusions, which were trapped during early diagenesis at about 2.4 Ga under oxygenated conditions. Microstructural evidence ( e.g . dislocations in dolomite from hematite inclusions) point to maximum T

Magnetism of natural composite of halloysite clay nanotubes Al2Si2O5(OH)4 and amorphous hematite Fe2O3

The natural composite of tubular mineral halloysite Al2Si2O5(OH)4 and nanoparticles of poorly crystallized or amorphous hematite Fe2O3 were investigated by means of transmission electron microscopy, electron spin resonance, Mössbauer spectroscopy and quantitatively characterized in measurements of low temperaturemagnetic susceptibility χ. The diamagnetic response χdiaof the halloysite nanotubes is superimposed on complex paramagnetic behavior χpara due to the presence of iron impurities in various aggregate forms. The low temperature upturn in χ(T) dependence is ascribable to isolated Fe3+ ions substituting Al3+ions, the step-like anomaly at Tg~80K is the signature of glassy magnetic order in nanosized inclusions of amorphous hematite.

Temporal constraints on genesis of the Caravia-Berbes fluorite deposits of Asturias, Spain, from paleomagnetism

The Caravia-Berbes district is a major fluorite producing area in Europe. The fluorite occurs as mantos replacing breccio-conglomerates of the Middle Permian Caravia Formation and as veins and irregular replacive bodies in the unconformably underlying limestone of the Late Carboniferous Caliza de Montaña Formation. Paleomagnetic analyses were done using alternating field and thermal step demagnetization and saturation remanence methods. Ten sites (82 specimens) in massive and disseminated fluorite ore from the Emilio manto yielded a stable chemical remanent magnetization (CRM) in hematite inclusions with a direction of Decl. 20.1°, Incl. 67.3° (α95=6.1°). After correction for Neogene Pyrenean tilt, the manto's paleoinclination gives a CRM acquisition age of 206±8Ma that dates a major hydrothermal and ore emplacement event. The age is coeval with the onset of Pangea's break up as the Iberian microplate began to split from the Armorican terrane of Eurasia as part of the ocean-forming CAMP (Central Atlantic Magmatic Province) event. Another 11 sites (109 specimens) of silicified dolostone of the Caliza de Montaña Formation just below the Cueto L'Aspa manto yielded a stable CRM that resides in single and pseudosingle domain magnetite inclusions that has a direction of Decl. 328.7°, Incl. 76.6° (α95=4.9°). After Neogene tilt correction, the altered zone's paleopole gives a CRM acquisition age of 115±3Ma. This age shows that the western Cantabrian basin also underwent a major hydrothermal alteration and remagnetization event by fluid flow through steep re-activated faults when Iberia rotated 35±2° away from Eurasia during Aptian-Albian time.

Structure formation processes of composites on the base of hazardous electric arc furnace dust for production of environmentally clean ceramics

The use of industrial wastes, especially of hazardous wastes, to substitute traditional natural raw materials is one of the most urgent problem to prevent environmental tragedies on our planet. This paper experimentally confirms that one of the most hazardous industrial waste from the steel-making process, i.e., electric arc furnace dust (EAFD), can be used as a valuable component in composite ceramic production, which uses other industrial wastes, such as foundry sands, galvanic glass microspheres and acid neutralization salt. The total percentage of industrial waste used as raw materials reached 85%. Only a small amount of a traditional brick factory's clay-sand mixture (15–25%) was used to produce the ecologically safe ceramics. All of the wastes that were used as raw material contained varying amounts of heavy metals in quantities that greatly exceeded the sanitarium norms. The ceramics were sintered at 900°, 950°, 1000°, 1050° and 1100 °C and exhibited flexural strengths that reached 13.97 MPa with extremely low leaching and solubility of metals. XRD, SEM, EDS and LAMMA methods determined the appearance of the vast areas of glassy structures with small inclusions of mullite, hematite, anorthite, thenardite and quartz. Almost complete (till 85%) replacement of natural raw materials with hazardous industrial wastes could significantly improve (32–46%) the flexural strength and others mechanical properties of the ceramics. Therefore, the use of hazardous industrial waste enhances the ceramics properties and improves the quality of environment because of high heavy metals (Sn, Pb, Zn) content with very low melting points.

High-resolution dielectric characterization of minerals: A step towards understanding the basic interactions between microwaves and rocks

Microwave energy was demonstrated to be potentially beneficial for reducing the cost of several steps of the mining process. Significant literature was developed about this topic but few studies are focused on understanding the interaction between microwaves and minerals at a fundamental level in order to elucidate the underlying physical processes that control the observed phenomena. This is ascribed to the complexity of such phenomena, related to chemical and physical transformations, where electrical, thermal and mechanical forces play concurrent roles. In this work a new characterization method for the dielectric properties of mineral samples at microwave frequencies is presented. The method is based upon the scanning microwave microscopy technique that enables measurement of the dielectric constant, loss factor and conductivity with extremely high spatial resolution and accuracy. As opposed to conventional dielectric techniques, the scanning microwave microscope can then access and measure the dielectric properties of micrometric-sized mineral inclusions within a complex structure of natural rock. In this work two micrometric hematite inclusions were characterized at a microwave frequency of 3GHz. Scanning electron microscopy/energy-dispersive x-ray spectroscopy and confocal micro-Raman spectroscopy were used to determine the structural details and chemical and elemental composition of mineral sample on similar scale.

Effects of dust particle internal structure on light scattering

Abstract. There is a large variety of internal structures inside atmospheric dust particles, making them inherently inhomogeneous. Such structures may have a large effect on ground-level and atmospheric radiation. So far, dust particle internal structures and their effect on the light scattering properties have proved to be hard to quantify, in part due to challenges in obtaining information about these structures. Recently, internal structures of individual dust particles were revealed through focused ion beam milling and analyzed. Here, we perform a sensitivity study to evaluate the optical impacts of some of the typical internal structures revealed. To obtain suitable model particles, the first step is to generate inhomogeneous particles with varying internal structures by using an algorithm that is based on three-dimensional Voronoi tessellation. The parameters for the particle generation are obtained from studies of real-world Asian dust particles. The second step is to generate homogeneous versions of the generated particles by using an effective-medium approximation, for comparison. Third, light scattering by both versions of these particles is simulated with discrete dipole approximation code. This allows us to see how different internal structures affect light scattering, and how important it is to account for these structures explicitly. Further, this allows us to estimate the potential inaccuracies caused by using only homogeneous model particles for atmospheric studies and remote-sensing measurements. The results show that the effects vary greatly between different kinds of internal structures and single-scattering quantity considered, but for most structure types the effects are overall notable. Most significantly, hematite inclusions in particles impact light scattering heavily. Furthermore, internal pores and hematite-rich coating both affect some form of light scattering noticeably. Based on this work, it seems that it is exceedingly important that the effects of dust particle internal structures on light scattering are accounted for in a wide variety of applications.

Experimental constraints on formation of hematite in olivine at high pressures and temperatures

Iron-rich oxides, such as magnetite or hematite, have been reported in olivine grains in many orogenic garnet peridotites from continental collision zones. Whether these iron-rich minerals originate from dry oxidation, dehydrogenation-oxidation or exsolution from a precursor wadsleyite phase is debatable. This paper explores high-pressure and high-temperature experiments in a hydrous harzburgite system, by taking advantage of electron backscattered diffraction (EBSD) analyses, to examine the formation of hematite in olivine. Experimental results show that hematite can be formed within olivine grains at pressures >6 GPa and temperatures in the 1073–1473 K range. EBSD analysis suggests that hematite rods (not associated with clinopyroxene) and host olivine have the following crystallographic relations: \( \langle 0001 \rangle _{\text{Hem}} // [100]_{\text{Ol}} , \langle 10{-}10\rangle _{\text{Hem}} //[001]_{\text{Ol}} , \langle 11{-}20\rangle _{\text{Hem}} //[010]_{\text{Ol}} \), which are consistent with those observed in natural garnet peridotite from the Dabie–Sulu ultra-high-pressure (UHP) metamorphic terrane. It is postulated that both hydroxide (OH−) and hydrogen (H+) ions have the potential to oxidize Fe2+ to Fe3+, followed by rapid dehydrogenation and slow Fe diffusion, thus forming hematite within the olivine grains. It is proposed that dehydrogenation-oxidation is the most likely formation mechanism of hematite inclusions within olivine, with the following two requirements: an ample amount of H2O and specific P–T conditions (>6 GPa, at 1073 K). Such conditions are consistent with those calculated in natural garnet peridotites from the Dabie–Sulu UHP metamorphic terranes. The present study also indicates that hematite (or magnetite?) inclusions in olivine contain important clues about the tectonic evolution of UHP rocks in continental crust collision zones.

Modelling radiometric properties of inhomogeneous mineral dust particles: Applicability and limitations of effective medium theories

The effect of inhomogeneous mineralogical composition on the optical properties of mineral dust particles is investigated. More specifically, spheres composed of a non-absorbing mineral with multiple spherical hematite inclusions are considered. The size of the particles, the number of inclusions, and the hematite volume fraction are varied, and the differential and integral optical properties are compared to those computed for homogeneous spheres. The effective refractive index of the homogeneous spheres is obtained (i) by use of four conventional effective medium approximations; and (ii) by freely varying the real and imaginary parts of the refractive index until a best-fit of the scattering matrix elements is achieved for all scattering angles and particle sizes. Among the integral radiometric observables, the single scattering albedo is most sensitive to particle inhomogeneity, while the extinction and scattering efficiency and the asymmetry parameter are rather insensitive. The phase function, the degree of linear polarisation, the linear depolarisation, and, indeed, all elements of the scattering matrix are strongly modulated by particle inhomogeneity. None of the effective medium approaches, not even the best-fit method, are able to reproduce the single scattering albedo and the scattering matrix elements over the entire range of particle sizes.

Oxidation of Magnetite(100) to Hematite Observed by in Situ Spectroscopy and Microscopy

We study where and how hematite (α-Fe2O3) nucleates and grows during the oxidation of magnetite(100) single crystals. Hematite inclusions grow along ⟨110⟩ directions of the magnetite (Fe3O4), leading to a biaxial array of hematite slabs in an electrically conducting matrix of magnetite. The slab arrays form in both bulk single crystals and thin films of magnetite. Atomic force microscopy reveals that the surface growth of magnetite that accompanies hematite formation is faster adjacent to the hematite slabs. In situ X-ray photoelectron and X-ray absorption spectroscopies at 600 °C in an oxygen environment reveal that the conversion of the Fe2+ in magnetite to Fe3+ in hematite occurs without the formation of the metastable phase maghemite (γ-Fe2O3). We offer an explanation of why Fe3O4(100) oxidizes faster than Fe3O4(111).

Element mobilization during feldspar metasomatism: an experimental study

Albitization of K-feldspar has been studied experimentally at 500 and 750 °C and 200 MPa using concentrated NaCl solutions. The partially reacted feldspar grains were characterized using X-ray diffraction, electron probe microanalysis, transmission electron microscopy as well as Raman and laser-induced photoluminescence spectroscopy. The replacement of K-feldspar by albite occurs via coupled dissolution-reprecipitation due to the mobilization of K in exchange for Na and results in the mobilization of minor elements like Ba, Fe, Ti, and Mg. The release of tetrahedrally incorporated Fe 3+ and Ti 4+ in K-feldspar is temperature-dependent resulting in increasing mobilization with increasing temperature. Barium shows a positive correlation with K in the reacted areas. Replacement also leads to the formation of cogenetic rutile and Fe-rich pseudobrookite inclusions in the albitized regions. This supports the proposal that the Fe responsible for the formation of hematite inclusions in altered, natural alkali feldspars can originate from the feldspar.

Raman spectroscopy in gemmology as seen from a ‘jeweller's’ point of view

Some gemstones (diamonds, coloured stones or assembled gems) found in the jewellery commerce, when observed by an optical microscopy or even at naked eye, exhibit unusual characteristics, such as inclusions incorporated at different depths. The investigation by confocal Raman micro‐spectroscopy allowed identification of a blue sapphire and of nanocrystalline anatase in the same surface region of a cut and polished diamond. Moreover, hematite (α‐Fe2O3) inclusions of rectangular shape, embedded at different depths, ranging from a few microns to some tens of microns beneath the gemstone surface, were identified in the coloured stones. Finally, a detailed study of an assembled gem evidenced spectral features that can be put in relation with its fabrication process. Copyright © 2012 John Wiley & Sons, Ltd.

Mechanical properties of polymer concretes containing different amount of hematite or colemanite

Polymer concretes (PCs) were created by using varying concentrations of silica sand as aggregate and also hematite, colemanite and a commercial epoxy resin. Hematite is known to exhibit radiation shielding properties. Mechanical performance was evaluated including unit weight, pulse velocity, compressive strength, flexural strength, splitting tensile strength, modulus of elasticity and dynamic elastic modulus. As expected, mechanical properties depend on the resin concentration, the aggregate type and aggregate content in the mixture. Hematite particles have a larger effect than colemanite on mechanical properties of PCs. Inclusion of hematite provides significant improvement of the mechanical properties studied PCs in comparison to PC with silica sand only.

Empirical Pt7Cu from an alluvial platinum concentrate and its significance for platiniferous quartz lodes in the Lubero region, DR Congo

An alluvial platinum grain from Lubero, DRC, is compositionally analogous to Pt 7Cu. This phase is so far unknown in nature, but is known from the binary platinum-copper system to have an ordered structure and formed below 500 °C, and as low as 100 °C. Such low temperatures rule out magmatic platinum mineralisation as source rock. The presence of previously reported inclusions of vein quartz and hematite in some alluvial grains of platinum, together with the relatively low formation temperatures of the Pt 7Cu compound, suggests that hydrothermal quartz lodes were the source of the platinum found in the Lubero alluvia. © 2012 E. Schweizerbart'sche Verlagsbuchhandlung Stuttgart Germany.

Heavy minerals and the characters of ilmenite in the beach placer sands of Chavakkad-Ponnani, Kerala Coast, India

Indian beach placer sand deposits are, in general, ilmenite-rich. However, some concentrations are dominated by pyriboles. The Chavakkad-Ponnani (CP) area along the northern Kerala coast is one such deposit. This paper deals with the general character of the heavy minerals of CP with special emphasis on the characters of ilmenite. Most Indian beach sand ilmenites are of good quality. However, our observations on the ilmenites of CP using Optical Microscope, SEM and EPMA reveals that these are mineralogically very complex. The CP ilmenite varies from pure ilmenite to highly impure variety having intergrowths and inclusions of other oxide and silicate minerals. Ilmenite occurs as mixcrystals and forms intergrowth structure with hematite and Ti-hematite/ulvospinel; contains inclusions of hematite, quartz, and monazite. On the other hand ilmenite also occurs as inclusions within hematite and garnet. The pyriboles are dominantly amphiboles with hornblende-composition. Interestingly an inclusion of gold has been recorded within amphibole of hornblende composition. Garnets are mostly of almandine and pyrope type. Subordinate heavy minerals are sillimanite, zircon and rutile. Characteristic morphology, mineralogy and chemistry of amphibole, garnet and ilmenite together indicate that the placer sands of CP area are derived from the amphibolites, granite gneisses and basic igneous rocks lying in the hinterland towards the eastern border of Kerala. Though the overall quality of ilmenite is poor, highgrade ilmenite concentrate can be generated (of course with lower yield), by adopting precise mineral processing techniques. The CP deposit can be considered as a second-grade deposit but it has potential for future exploitation.

Nano encapsulation of hematite into silica matrix as a red inclusion ceramic pigment

The hematite as a natural and non toxic red inorganic pigment has been known since prehistoric times but color shade of hematite becomes unstable with temperature and need to protect with a suitable matrix. The best red shades are obtained by the inclusion of hematite in silica matrixes. A co-precipitation method has been applied in order to improve the inclusion efficiency of hematite into silica crystals; iron sulfate was used as Fe precursor and precipitating agent was ammonia. Effects of the single flux agent (NaF and NaCl) and binary flux agent (NaF·NaCl), have been studied. Continuous changes in color were measured by comparing L*- a*- b* values of the heated samples. TEM analysis on heat treated powders shows some hematite single crystals that were occluded with silica crystals successfully. Due to its chemical and thermal stability, the hematite/silica pigment may be considered as a suitable red pigment for ceramic manufacturing by fast firing cycles.