Physicochemical properties of talc ore from three deposits of Lamal Pougue area (Yaounde Pan-African Belt,Cameroon), in relation to industrial uses

Three talc deposits were discovered at Ngoung, Lamal Pougue and Bibodi Lamal (Cameroon). They derived from ultramafic rocks and are enclosed in a Pan-African garnet and muscovite-bearing mica schist of the Yaoundé series. The physico-chemical properties of these talc deposits have been investigated by different techniques including Scanning Electron and Transmission Microscopy (SEM and TEM), chemical analyses, X-ray diffraction (XRD), infrared spectroscopy, particle size analysis by laser diffraction and low temperature gas absorption–desorption. The mineralogical composition deduced from XRD is wide (talc + chlorite + tremolite ± anthophyllite ± chromite ±serpentine ± brucite ± magnesite ± dolomite), but due to the high talc contents (≈ 90%) the samples are close to monomineralic. SEM studies reveal that all talc deposits comprise bundles of platy talc and a few prismatic crystals of amphiboles and other contaminating minerals. Laser diffraction confirms the coarse particle size of the talc crystals. Mode values are as high as 105–170 μm (except two samples displaying 76 and 42 μm) and d50 ranges from 107 to 25 μm. The values of specific surface area measured by BET and t-plot methods range from 1 to 6 m²/g and are correlated with external specific surface area measured by laser diffraction. Discrepancies from the trend are due to the semi-crystalline texture of the samples and mostly to intra-crystalline structural defects revealed by TEM observations. In infrared spectra, specific absorption bands are distinguished for talc, chlorite, tremolite, carbonates, serpentine, brucite and water. Occasional substitutions in minerals led to a shift in some absorption bands. The chemical composition criteria important for most of the industrial applications such as ceramics and pharmaceutics are closely complied with in untreated samples from these deposits. In summary, high talc proportions, chemical compositions, platy morphology and coarse grain size of its crystals lead to the conclusion that the studied deposits are economically attractive. The data set of the present work is an important tool for choosing the beneficiation methods for specific applications.     

Adsorption and binding of the transgenic plant proteins, human serum albumin, β-glucuronidase, and Cry3Bb1, on montmorillonite and kaolinite: Microbial utilization and enzymatic activity of free and clay-bound proteins

Human serum albumin (HSA), β-glucuronidase (GUS), and the Cry3Bb1 protein from Bacillus thuringiensis subsp. kumamotoensis are expressed by genetically-modified plants. Commercial samples of these proteins adsorbed and bound rapidly on the clay minerals, kaolinite (K) and montmorillonite (M). Adsorption increased as the concentration of protein increased and then reached a plateau. The greatest amount of adsorption and binding occurred with the Cry3Bb1 protein, of which there was no desorption: 6.7 ±0.21 μg adsorbed and bound μg^− 1 of M; 2.1 ± 0.39 μg adsorbed and bound μg^− 1 of K. With GUS, 2.2 ± 0.29 μg adsorbed and 1.7 ±0.21 μg bound μg^− 1 of M; 1.5 ± 0.28 μg adsorbed and 1.0 ± 0.03 μg bound μg^− 1 of K. HSA was adsorbed and bound the least: 1.2 ±0.04 μg adsorbed and 0.8 ± 0.05 μg bound μg^− 1 of M; 0.4 ± 0.05 μg adsorbed and 0.4 ± 0.03 μg bound μg^− 1 of K. However, X-ray diffraction analyses indicated that only HSA intercalated M, and none of the proteins intercalated K, a nonswelling clay. When bound, the proteins were not utilized for growth by mixed cultures of soil microorganisms, whereas the cultures readily utilized the free (i.e., not adsorbed or bound) proteins as sources of carbon and energy. The enzymatic activity of GUS was significantly enhanced when bound on the clay minerals. These results indicated that recombinant proteins expressed by transgenic plants could persist and function in soil after release in root exudates and from decaying plant residues as the result of the protection provided against biodegradation by binding on clay minerals.     

Preparation of Co–Al layered double hydroxides by the hydrothermal urea method for controlled particle size

In order to control particle size and the distribution, Co–Al layered double hydroxides were prepared from aqueous glycerol solutions of cobalt chloride and aluminum chloride by urea hydrolysis under hydrothermal conditions. Effects of the synthetic conditions including heating temperature and time, and glycerol/water ratio on the particle size and its distributions of Co–Al layered double hydroxide were discussed. Particle diameter was controlled from 1.0 (glycerol/water ratio = 10 g/40 mL) to 38.3 μm (glycerol/water ratio = 0 g/40 mL, heating at 50 °C for 150 days). Narrow particle diameter distribution as low as 20% coefficient of variation was achieved under optimized synthetic conditions (glycerol/water ratio = 10 g/40 mL, heating temperature < 80 °C).     

Effects of sand addition on production of lightweight aggregates from Tunisian smectite-rich clayey rocks

Smectite-rich claystone–marlstone samples from 12 outcrops located in the Southern Atlas domain of Tunisia were investigated with regard to manufacture of lightweight aggregates (LWAs). The clayey materials mainly consist of smectite, kaolinite and illite, together with quartz, calcite, dolomite and feldspars as accessory components. 10–12 mm pellets were prepared from wet paste and initially heated to 600 °C, 700 °C or 800 °C (depending on the raw material) for at least 2 h in order to avoid any explosion of the aggregate. The pellets were then subjected to a quick firing process at 1180 °C. The addition of 15% of quartz sand (< 250 μm grain size) to the raw materials was found to improve some required pre-treatments and give better expansion properties to some of the aggregates. The addition of 1% used automobile oil to the clay and quartz sand mixtures caused the formation of more gas and a drop in bloating temperature. The obtained LWAs were characterized by physical properties such as apparent density, mechanical resistance, water absorption and expansion. The laboratory results were comparable to those of two commercial LWAs from France (Argidécor®) and Portugal (LECA®) and provide new openings for the utilization of Tunisian claystone in civil engineering work or in agricultural applications.     

Characterization of smectite after acid activation with microwave irradiation

The effect of acid activation under microwave (MW) irradiation on the textural and structural properties of a smectite from Maghnia (Algeria) was investigated.Sample aliquots were treated with 2 M hydrochloric acid for various times under variable irradiation power. The influence of activation parameters (MW power and time duration) on the textural and structural properties of the activated samples (crystallinity, specific surface area, pore volume, pore diameter, porosity, pore size distribution and morphology) have been studied.The prepared materials were characterized by X-ray diffraction, Differential Thermal and Thermo Gravimetric Analysis (DTA and TGA), Scanning Electron Microscopy (SEM) and nitrogen adsorption/desorption to obtain information about their structure and surface texture.The treated samples consisted of microporous and mesoporous structures. The specific surface area, pore diameter and pore volume of an adsorbent prepared by the microwave-heating method were 165.80 m²/g, 50 nm and 0.1919 cm³/g, respectively. The pore volumes of mesopores and micropores were 163.90 · 10^− 3 and 28.89 · 10^− 3 cm³/g, respectively. Furthermore, small pores were created in the prepared materials with microwave irradiation.     

Dissolution kinetics of dehydroxylated nickeliferous goethite from limonitic lateritic nickel ore

The dissolution kinetics in 2 M H₂SO₄ of variously dehydroxylated nickeliferous goethites was investigated for five oxide-type lateritic nickel deposits. Goethite was the main constituent with minor amounts of quartz, talc, kaolinite and Mn oxides. Dissolution of Fe from heated materials followed the Kabai equation. There was a 9–34-fold increase in the Kabai dissolution rate constant (k) for samples heated at 340–400 °C due to both the increased surface area (1.5–2.6 fold) and higher density of structural defects (5–10 fold) in the variously dehydroxylated products. The presence of structural Al and Cr in goethite appears to reduce dissolution rate possibly through the greater M³⁺–OH, O bond strength relative to Fe³⁺, Ni²⁺–OH, O. Nickel showed congruent dissolution with Fe indicating that Ni was uniformly incorporated in the goethite structure. Pre-heating goethite to 600–800 °C for 30 min resulted in incongruent dissolution of Fe and Ni. It is postulated that some Ni is ejected from the neo-formed hematite structure and resides on the crystal surface or in voids. These results may contribute to the development of more efficient procedures for Ni extraction including heap leaching of lateritic nickel ores.     

Surfactant-modified bentonite as adsorbent for the removal of humic acid from wastewaters

The effectiveness of surfactant-modified bentonite (SMB) in removing humic acid (HA) from wastewaters was evaluated. Hexadecyl trimethylammonium (HDTMA) chloride was used to modify the surface of the clay mineral. The SMB exhibits very high adsorption potential for HA and at pH 3.0 more than 99% removal was achieved from an initial concentration of 25 μmol/L. The experimental kinetic data were analyzed using the pseudo-first-order kinetic model. Adsorption occurs through film diffusion at low as well as at higher concentrations and temperatures. The adsorption of HA using SMB was an exothermic process. HA adsorption was found to decrease with increase of ionic strength due to the formation of outer-sphere surface complexes on SMB. The equilibrium isotherms were determined and data were analysed using the Langmuir isotherm model. The maximum adsorption capacity, Q° was 73.52 μmol/g with binding constant, b = 0.155 L/μmol at 30 °C and pH 3.0. The adsorbent was suitable for repeated use (more than 3 cycles) without any noticeable loss of capacity.     

Effect of particle size on cesium exchange kinetics by K-depleted phlogopite

Cation exchange mechanism and rate of Cs⁺ exchange were investigated in < 2 μm and 20–2 μm particle size fractions of K-depleted phlogopite (Na-phlogopite). The K-depleted phlogopite was prepared from a natural phlogopite by a potassium removal method using sodium tetraphenylborate (NaTPB) at room temperature. X-ray diffraction (XRD) patterns revealed that interlayer K⁺ ions were completely replaced with sodium ions after the potassium removal treatment. Ion exchange isotherms and kinetics were determined for Na⁺ → Cs⁺ exchange with two particle size fractions. The isotherms indicated that both particle size fractions showed high selectivity for Cs⁺. Based on the isotherm tests, ΔG^o values of < 2 μm and 20–2 μm particle fractions were − 6.83 kJ/mol and − 7.08 kJ/mol, respectively. Kinetics of Cs exchange revealed that the 20–2 μm particle size fraction of the K-depleted phlogopite took up more Cs⁺ ions than the < 2 μm particle size fraction. Various kinetic models were applied to describe Na⁺ → Cs⁺ exchange process. Elovich model described the kinetic data of the < 2 μm particle size fraction well, while the modified first-order model or parabolic diffusion model described the data of the 20–2 μm particle size fraction well.     

A comparison of diamonds irradiated by high fluence neutrons or electrons, before and after annealing

Neutron- and electron-irradiated type Ia “black” diamonds were analyzed: three near colorless type Ia diamonds were treated in a nuclear reactor with a dose of 1.8 × 10¹⁷ neutrons/cm² and three equivalent samples were irradiated in an electron accelerator with a dose of approximately 0.5 GGy 10 MeV electrons. The diamonds were then annealed and analyzed after the different steps of the treatment. The samples turned from near colorless to very dark green to opaque black upon irradiation and deep greenish yellow to deep orangy brown upon annealing (Fig. 1). The amount of brown color developed during the treatment was found to relate to the type of irradiation used and likely to the total dose of irradiation. The absorption and photoluminescence features as well as the color changes that were observed were found to be unusual and characteristic for diamonds treated with such high irradiation doses. Certain spectral features such as the 644/649 nm, the 724/734/738 nm, the 920 nm and the 967 nm absorptions were only detected in the neutron-irradiated diamonds while others such as the 6165 cm^− 1 and the 805 nm absorptions were only found in the spectra of the electron-irradiated stones.In addition to these treatment experiments some neutron-irradiated very dark green (appearing black) diamonds were heated from 300 to 1100 °C in increments of 50 °C to get a precise idea of the temperature at which color changes occur and the various absorption peaks form. All diamonds turned yellowish to orangy brown after annealing above 700 °C and most of them exhibited unusually strong H1b and/or H1c absorptions after annealing at > 900 °C.     

Adsorption of gaseous SO2 and structural changes of montmorillonite

Several montmorillonite samples after adsorption of gaseous SO₂ were analyzed to evaluate structural and textural changes. The equilibrium adsorption of the SO₂ gas was measured at 25 °C and 0.1 MPa. The samples were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), swelling index (SI), pH measurements, and N₂ adsorption–desorption isotherms. SO₂ adsorption increased with the specific surface area of montmorillonite. SO₂ retention decreased pH of the dispersed samples from 6 to 1 and released interlayer and octahedral cations from the structure, which increased the specific BET surface area and specific micropore surface similar to that of acid-activated montmorillonite.     

Homoepitaxial CVD diamond: Raman and time-resolved PL characterization

In this work, we report on the structural characterization of homoepitaxial Microwave Plasma Enhanced CVD diamond grown onto Ib diamond substrates by varying systematically the methane to hydrogen ratio in the gas mixture (1–7% CH₄). X-ray diffraction, Raman spectroscopy and photoluminescence (PL) have been used to characterize the diamond samples. Raman measurements pointed out the excellent crystalline quality and phase purity of the specimens. PL measurements in the 1.7–2.7 eV energy range have shown completely flat spectra, excluding the presence of nitrogen-related optical centers. Such results show that the homoepitaxial CVD diamond can be grown, at moderate microwave power (720 W), and at growth rates not too low ( 1 μm/h) preserving a good quality. Moreover, the homoepitaxial crystals exhibited a strong free-exciton recombination radiation at room temperature even at the highest methane concentration used (7%). Preliminary measurements of the lifetime of the free exciton at room temperature have been also performed. The excitation was produced by a 5 ns pulsed laser irradiation at energies above the diamond band gap. The results have been compared with the structural properties of the samples and correlated with the growth conditions.     

Characterization of sepiolite as a support of silver catalyst in soot combustion

Turkish sepiolite–zirconium oxide mixtures were applied as a support for the silver catalyst in a soot combustion. Sepiolite–Zr–K–Ag–O catalyst was characterized by XRD, N₂ adsorption, SEM, TPR-H₂ and EGA-MS. The combustion of soot was studied with a thermobalance (TG-DTA). The modification resulted in a partial degradation of the sepiolite structure, however, the morphology was preserved. The adsorption of N₂ of the modified sepiolite is a characteristic for mesoporous materials with a wide distribution of pores. The specific surface area S_BET equals 83 m²/g and the pores volume is 0.23 cm³/g. The basic character of the surface centers of sepiolite is indicated by CO₂ desorption (TPD-MS) at 170 °C and at about 620 °C due to a surface carbonates decomposition. The thermodesorption of oxygen at 650–850 °C indicates the decomposition of AgO_x phases at the surface. The presence of AgO_x phases is also confirmed by TPR-H₂ spectrum (low temperature reduction peak at 130 and 180 °C). The high-temperature reduction at about 570 °C is probably related to Ag–O–M phases on the support.The soot combustion takes place at T₅₀ = 575 °C. Without silver (sepiolite–Zr–K–O) T₅₀ = 560 °C but sepiolite modified with silver (sepiolite–Zr–K–Ag–O) undergoes the same process at T₅₀ = 490 °C.     

Pakistani bentonite in mortars and concrete as low cost construction material

A Pakistani bentonite, in “as is” (21 °C) and “heated” (150 °C, 250 °C, 500 °C, 750 °C and 950 °C) conditions, was incorporated in mortar cubes, concrete cylinders and concrete beams as a partial substitute for Ordinary Portland cement (OPC) and studied in detail. Results showed that OPC mortars and concrete containing 20% “as is” and 25% “heated to 150 °C” bentonite could be used as low-cost construction materials. They will also reduce energy consumption, preserve natural resources and solve environmental problems related to cement production as well as augment the durability and life cycle of the concrete structures.The X-ray diffraction patterns showed that bentonite possessed both crystalline and amorphous phases. The strength activity indices (SAI) after 7 and 28 days were higher than 75% for “as is” and “heated” bentonite, except for the 950 °C samples, which was below the ASTM C618 specified limit of 75%. The maximum SAI was shown by “150 °C heated” bentonite. The compressive strength data also showed similar results for OPC mortar cubes and concrete cylinders containing “150 °C heated” bentonite. When compared with the control mixture, the compressive strength values were the same as for mortar containing 25% bentonite as replacement of OPC. However, these values decreased in concrete initially and started to gain strength remarkably after 28 days. Resistance to sulphate attack and water absorption tests on mortar cubes soaked in 2% magnesium sulphate and 5% sodium sulphate solutions demonstrated consistent improvement as the bentonite content in them was increased. The modulus of rupture of all concrete beams decreased as the OPC substitution level by bentonite increased from 20% to 40%. Bond strength of OPC mortar containing 20% “as is” and 25% “heated to 150 °C” bentonite in brick prisms was almost the same as that of control mixture.     

Spectroscopic and porosimetry studies to estimate the firing temperature of some archaeological pottery shreds from India

The present study aims to estimate the firing temperature of archaeological pottery shreds collected from the three archaeological sites namely Maligaimedu, Thiruverkadu and Palur in Tamilnadu state, India. The spectroscopic method Fourier Transform Infrared Spectroscopy (FT-IR) has been employed to find the lower limit of firing temperature of the archaeological pottery shreds by refiring the samples to four different temperatures from 200 °C to 800 °C. From the observation of the hydroxyl band and appearance/disappearance of octahedral sheet structure the firing temperature of the shreds has been estimated. The samples from Maligaimedu site named as MM1, MM3 and MM5, Thiruverkadu and Palur samples were fired to a temperature above 800 °C and the samples of Maligaimedu MM2, MM4 and MM6 were fired below 800 °C. Additionally, porosimetry measurements such as water absorption and mercury intrusion (MIP) were also carried out. The samples MM1, MM3, TK2–TK6, PL3 and PL5 were fired to a temperature less than 900 °C and the other samples to less than 1000 °C.     

Mineralogical transformations of calcareous rich clays with firing: A comparative study between calcite and dolomite rich clays from Algarve, Portugal

Mineralogical transformations during firing of two extremely calcareous clays, one calcite and other dolomite rich, and relatively poor in silica were studied. Original clays were mineralogical and chemically characterized with X-ray diffraction (XRD) and X-ray fluorescence (XRF). Firing of both clays was carried out in the temperature range 300–1100 °C under oxidizing conditions and the mineralogical transformations were investigated with XRD, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscopy associated with energy dispersive X-ray spectroscopy (SEM-EDS).Important compositional differences in the neoformed phases were observed between calcite and dolomite rich clays. In the Ca-rich clay the assemblage gehlenite + wollastonite + larnite was observed. In the Mg(Ca)-rich clay the reaction products included akermanite, diopside, monticellite, forsterite, periclase and spinel.XRD and SEM-EDS showed the presence, in both clays, of a potassium–calcium sulfate in samples fired between 900 and 1100 °C.     

Preparation and mechanical properties of exfoliated mica-polyamide 6 nanocomposites using sericite mica

A new mica/polyamide 6 (PA6) nanocomposite was formed by exfoliation of a mica, potassium sericite (K⁺-SE). The powder sample was separated through an air-classifier into D₅₀:6.0 μm (median particle diameter), D₁₀:3.5 μm, and D₉₀:9.5 μm. The K⁺-SE was modified with a dodecylammonium salt (DDA) by ion exchange at 70 °C for four days. The resulting organically modified SE was melt-kneaded with PA6 in a twin-screw kneader at 260 °C. In order to characterize the nanocomposite morphology, X-ray diffraction and transmission electron microscopy were used. Differential scanning calorimetry and mechanical property measurements were also carried out. The morphology of the nanocomposite revealed mica nanolayers with very high aspect ratios; that is, at levels about two times greater than that of conventional exfoliated clay-polymer nanocomposites. A small amount of organically modified SE with 2.1 mass% silicate was sufficient to improve the flexural properties and heat distortion temperature of the nanocomposite. However, overall mechanical properties were not completely improved, because the shearing stress induced during exfoliation of the silicate layers resulted in inhomogenous dispersion of silicate platelets in the matrix. The present study indicates that three factors, degree of exfoliation, aspect ratio and dispersion homogeneity of silicate platelets, play an important role for the development of high performance nanocomposites.     

Low-temperature thermionic emission from nitrogen-doped nanocrystalline diamond films on n-type Si grown by MPCVD

Temperature-dependent emission current–voltage measurements were carried out for nitrogen (N)-doped nanocrystalline diamond (NCD) films grown on n-type Si substrates by microwave plasma-assisted chemical vapor deposition (MP-CVD). Low threshold temperature (~ 260 °C) and low threshold electric field (~ 5 × 10^− 5 V/µm) were observed. Both the temperature dependence and the electric field dependence have shown that the obtained emission current was based on electron thermionic emission from N-doped NCD films. We have also studied the relation between nitrogen concentration and the saturation emission current. The saturation current obtained was as high as 1.4 mA at 5.6 × 10^− 3 V/µm at 670 °C when the nitrogen concentration was 2.4 × 10²⁰ cm^− 3. Low value of effective work function (1.99 eV) and relatively high value of Richardson constant (~ 70) were estimated by well fitting to Richardson–Dushman equation. The results of smaller φ and larger A′ suggest that N-doped NCD has great possibility of being a highly efficient thermionic emitter material.     

Dehydroxylation and dissolution of nickeliferous goethite in New Caledonian lateritic Ni ore

Goethite is a major constituent in ferruginous soils in a lateritic nickel deposit on the Koniambo massif in New Caledonia, and dehydroxylation of nickeliferous goethite may occur naturally due to fire and during the processing of lateritic Ni ore. Goethite started to alter to hematite in 2 h of heating at 230–250 °C and had completely altered to hematite at 340 °C and higher temperatures. For most heated samples the rate of dissolution of Fe in 1 M HCl followed the cube root equation with a single straight line describing the data, however for samples where both goethite and hematite were present the data did not conform to this equation. There was an approximately 7 fold increase in the rate of dissolution for samples heated to 340 °C which can be accounted for by the increase in surface area (2-fold) due to the development of micropores and the increase of structural defects in poorly ordered hematite structures (protohematite and hydrohematite) (3.5-fold) formed by partial dehydroxylation of goethite. For heated samples Ni, Cr, Al, Co and Mn showed congruent dissolution with iron indicating uniform incorporation of these metals in the structures of the iron oxides and complete retention of these metals in crystals during the goethite to hematite transition. V and Cu showed only partial dissolution (i.e. noncongruent dissolution) indicating that some V and Cu may be associated with another less soluble mineral (e.g. ilmenite).     

Adsorption of chromate and molybdate by cetylpyridinium bentonite

Bentonite was modified with cetylpyridinium bromide (CPBr) and investigated by elemental analysis, IR, X-ray diffraction, thermogravimetric analysis, specific surface area (BET) and electrokinetic mobility measurements. The surfactant was adsorbed on the montmorillonite in a bilayer structure. The organo-bentonite removed the oxyanions of Cr(VI) and Mo(VI) from aqueous solutions. The adsorption followed a pseudo-second-order kinetics and adsorption capacities of 0.7 and 1.4 mmol/g for Cr(VI) and Mo(VI) were recorded. E_a = 5.34 and 14.50 kJ/mol for the adsorption of Cr(VI) and Mo(VI) indicated an ion exchange mechanism. The standard free energy values (ΔG°) of − 2.11 and − 3.40 kJ/mol for Cr(VI) and Mo(VI) indicated a spontaneous adsorption process. Column studies showed the suitability of the organo-bentonite for operation in continuous flow systems.     

Clay minerals and iron oxides-oxyhydroxides as fingerprints of firing effects in a limestone monument

Different Portuguese limestones-Encarnadão, Amarelo de Negrais, Lioz and Gresoso-have been widely used as building materials and ornamental stones in the architecture of Lisbon (Portugal) area.The aim of the study of those materials was focused on fire-induced stone damage, mainly on identifying the thermal transformations of clay minerals and iron oxides-oxyhydroxides. Taking into account an applied component to the cultural heritage, a special attention was given to one of the most ancient Portuguese monuments — Lisbon Cathedral, specifically its cloister that was severely damaged by a fire that occurred right after the 1755 earthquake.A set of samples collected from outcrops were studied and subjected to artificial heating. The results were compared with those obtained from samples collected in the monument. XRD, SEM-EDS and ⁵⁷Fe Mössbauer spectroscopy were used. The < 2 µm fraction varies significantly between unheated (outcrop samples) and artificially heated samples, particularly in relation to iron oxides-oxyhydroxides. Kaolinite is the dominant clay mineral, followed by illite and smectite. Goethite is the iron oxyhydroxide characteristic of all studied lithotypes both in unheated samples and samples artificially heated to 250 °C. Encarnadão is the exception presenting hematite in those conditions. As firing temperature increases (300 °C–600 °C) disordered hematite appears at the expense of goethite, and smectite is no longer detected. Mössbauer spectra further reveal that Fe²⁺ in silicate minerals is fully oxidized at 600 °C but remains in the carbonate structure up to this temperature. The SEM-EDS analyses show that 2:1 clay minerals have Si and Al as main cations and minor amounts of K and Fe. It also shows that all the clay minerals and Fe-rich particles are always associated to the limestone porosity.. The present results show that the clay minerals, namely illite–smectite mixed-layer and smectite, can be used as indicators of stone provenance used in Lisbon Cathedral Cloister as well as fingerprints of the temperature achieved during the fire of Lisbon Cathedral that most likely was not higher than 350 °C.