Lucilene dos Santos

This study investigates the geochemistry of ornamental stones, with emphasis on chemical composition and its direct relationship with durability and susceptibility to chemical alterations under different exposure environments. X-ray Fluorescence (XRF) and Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS) were applied to identify and quantify the main constituent oxides: MgO, Al₂O₃, SiO₂, FeO, K₂O, CaO, TiO₂, MnO, Na₂O, and P₂O₅. The results indicate that the presence of mafic minerals rich in MgO increases the rock’s susceptibility to chemical alterations, especially in acidic or alkaline environments, favoring the development of stains, localized darkening, and matrix weakening. Conversely, the high contents of Al₂O₃ and SiO₂, mainly associated with feldspars and quartz, enhance chemical resistance, although feldspars may undergo partial dissolution under more aggressive conditions, releasing soluble cations that increase porosity. FeO, detected in significant concentrations, is directly linked to oxidation processes, which impair both the aesthetics and the structural integrity of the rock. Elements such as K₂O, CaO, and TiO₂ actively contribute to the formation of surface stains and efflorescences, while MnO, even in low concentrations, can cause darkening due to oxidation. Na₂O and P₂O₅, although present in minor proportions, influence reactivity and durability, contributing to secondary phenomena such as salt efflorescences and increased vulnerability to aggressive solutions. These results reinforce that mineralogical heterogeneity is a key factor in determining the physicochemical performance of ornamental stones when exposed to chemical weathering. In conclusion, this study contributes to the understanding of geochemical alteration processes in ornamental rocks, demonstrating that the interaction between major and accessory minerals defines their behavior when subjected to natural or artificial chemical agents. The main objective is to provide technical support for predicting the durability and aesthetic performance of ornamental stones under different usage conditions, thereby assisting both in the careful selection of materials for architectural projects and in the development of preventive conservation strategies in potentially aggressive environments.

In Brazilian territory many occurrences do not have their gemological and optical properties documented or made public. This research aimed to analyze the mineralogical and gemological aspects of emeralds from the city of Tauá (Brazil), utilizing gemological instruments such as a refractometer, dichroscope, spectroscope, polariscope, hydrostatic balance, ultraviolet lamp, and gemological microscope. The examined emeralds exhibit typical features found in emeralds worldwide, except for an above-average birefringence, similar to certain beryls from the state of Ceará. This highlights the significance of gemological characterization not only at the regional levels but also on a localized scale. Additionally, studying occurrences in varied geological settings is essential, as the formation environment influences mineral properties.

In this study, flotation tests were conducted on a laboratory scale using a sample of microcrystalline graphite ore from the Canindé region, Ceará, Brazil. The objective was to investigate the grinding time, reagent dosage, and purification process for obtaining graphene-based nanomaterials. Natural graphite has a stacked planar structure and exhibits polymorphism with rhombohedral, hexagonal, and turbostratic geometries, characteristics that directly influence its properties and technological applications. The results demonstrated that it was possible to obtain rougher concentrate with a graphite carbon content of 23.4% and a recovery of 86.4%, using a grinding time of 7.5 min and reagent dosages of 150 g/t of kerosene and 100 g/t of Flotanol D-25. This flotation process resulted in a graphite concentrate with 76.6% graphite carbon content. To increase the purity of the concentrate and expand its industrial applications, the graphite was purified in an alkaline autoclave using the hydrothermal method. In the next stage, acid leaching was performed, and this chemical treatment destabilized the regular stacking of the graphite layers, promoting the formation of graphene-like nanoplates, including monolayer graphene. Thus, the nanomaterials obtained through the process developed in this study have potential for various innovative applications, such as lithium-ion batteries, electric vehicles, and two-dimensional graphene-based materials.

In this study, flotation tests were conducted on a laboratory scale using sample of microcrystalline graphite ore from the Canindé region, Ceará, Brazil. The objective was to investigate the grinding time, reagent dosage, and purification process for obtaining graphene-based nanomaterials. Natural graphite has stacked planar structure and exhibits polymorphism with rhombohedral, hexagonal, and turbostratic geometries, characteristics that directly influence its properties and technological applications. The results demonstrated that it was possible to obtain rougher concentrate with a graphite carbon content of 23.4% and a recovery of 86.4%, using grinding time of 7.5 minutes and reagent dosages of 150 g/t of kerosene and 100 g/t of Flotanol D-25. This flotation process resulted in a graphite concentrate with 76.6% graphite carbon content. To increase the purity of the concentrate and expand its industrial applications, the graphite was purified in an alkaline autoclave using the hydrothermal method. In the next stage, acid leaching was performed, and this chemical treatment destabilized the regular stacking of the graphite layers, promoting the formation of graphene-like nanoplates, including monolayer graphene. Thus, the nanomaterials obtained through the process developed in this study have potential for various innovative applications, such as lithium-ion batteries, electric vehicles, and two-dimensional graphene-based materials.

The minerals have great importance through deposits, being widely used in the more traditional fields of geology (economic geology, prospecting, sedimentology, petrology / petrography). The aim of this research was the elaboration of a birefringence table, using only the optical properties, for a faster, safer, and more succinct identification of some important minerals in a petrographic section (0.03 mm), focusing on the most efficient characteristics and using the addition and subtraction colors related to birefringence, in which most of those analyzed are heavy minerals, as well as other very common minerals. The table prepared for this paper has two differential characteristics, which make it efficient. Updated values from birefringence in several minerals; plus, each combination color that could be visualized trough the accessory of 530 millimicron. Due to its ease and precision of use, it can be used by researchers, professionals and undergraduates. The table containing 42 common minerals, with the information on each of their character of optical signal, colors with quartz accessories, pleochroism, and the most relevant characteristic was chosen to facilitate the identification of such minerals.

Since the end of the 20th century, it has become extremely common for countries with a significant exploration of gemstones to catalog and disclose the properties of their gems for various purposes. This paper aimed to analyze the gemological characterization and geochemical aspects of aquamarines from the County region of the city of Quixeramobim (State of Ceara). Usual gemology equipment was used; in addition, we used a scanning electron microscope with energy dispersive system (SEM-EDS). The studied minerals have the standard characteristics of aquamarines from different parts of the world, except for above-average birefringence and the presence of fluorescence. In the case of Quixeramobim aquamarine studied, a linear correlation was noted involving the geochemistry and some gemological aspects. However, the studied gems diverge in four characteristics and chemical elements, if compared to the aquamarines of a nearby region, named Berilândia (CE). This demonstrates the importance of gemological characterization, not only at a state/regional level. The Quixeramobim aquamarines are unique within the Brazilian scenario.

Ediacaran–Cambrian magmatism in the Central Subprovince (Borborema Province, NE Brazil) generated abundant A-type granites. This study reviews published whole-rock and mineral chemistry data from thirteen Ediacaran–Cambrian A-type intrusions and a related dike swarm. It also presents new mineral chemistry and whole-rock data for one of these intrusions, along with zircon trace element data for five of the intrusions. Geochronological data from the literature indicate the formation of these A-type intrusions during a 55 Myr interval (580–525 Ma), succeeding the post-collisional high-K magmatism in the region at c. 590–580 Ma. The studied plutons intruded Paleoproterozoic basement gneisses or Neoproterozoic supracrustal rocks. They are ferroan, metaluminous to peraluminous and mostly alkalic–calcic. The crystallization parameters show pressure estimates mainly from 4 to 7 kbar, corresponding to crustal depths of 12 to 21 km, and temperatures ranging from 1160 to 650 °C in granitoids containing mafic enclaves, and from 990 to 680 °C in those lacking or containing only rare mafic enclaves. The presence of Fe-rich mineral assemblages including ilmenite indicates that the A-type granites crystallized under low ƒO₂ conditions. Zircon trace element analyses suggest post-magmatic hydrothermal processes, interpreted to be associated with shear zone reactivation. Whole-rock geochemical characteristics, the chemistry of the Fe-rich mafic mineral assemblages, and zircon trace elements in the studied granitoids share important similarities with A₂-type granites worldwide.

A revista Estudos Geológicos tem como objetivo divulgar trabalhos científicos em Geociências, resultado de investigações, relatórios técnicos e trabalhos de conclusão de curso de graduação, dissertações de mestrado e teses de doutorado. Apresenta publicação em fluxo contínuo e ocasionalmente um volume adicional especial, com temas relevantes em geociências.

A revista Estudos Geológicos tem como objetivo divulgar trabalhos científicos em Geociências, resultado de investigações, relatórios técnicos e trabalhos de conclusão de curso de graduação, dissertações de mestrado e teses de doutorado. Apresenta publicação em fluxo contínuo e ocasionalmente um volume adicional especial, com temas relevantes em geociências.

O Complexo Máfico-Ultramáfico Estratiforme de Tucunduba (CMUET) compreende uma intrusão acamadada com geometria elipsoidal, com eixo maior apresentando direção N025° e área de aproximadamente 4 km2, constituído de metapiroxenitos, metagabros e metagabronoritos intrudidos em rochas granito-migmatíticas de idade paleoproterozoica do Domínio Ceará Central (DCC), Província Borborema (PB), Nordeste do Brasil. Essa associação magmática é cortada por diques alcalinos de idade oligocênica, pertencentes ao Vulcanismo Messejana. As rochas máfico-ultramáficas são representadas por três zonas litológicas: Zona Ultramáfica de composição peridotítica e piroxenítica localizada na porção noroeste do complexo; Zona de Transição caracterizada por mistura de rochas piroxeníticas e gabroicas, com textura e estrutura variadas; e Zona Máfica de composição gabro-norítica, concentrada na porção sudeste, além dos bordos oeste e norte do corpo. As zonas formadoras do CMUET foram afetadas parcialmente por deformação e recristalização metamórfica, resultantes de metamorfismo regional em fácies granulito, evidenciado por textura de poligonização formada por cristais de ortopiroxênio e clinopiroxênio, bem como ocorrência de hercinita, experimentaram retrometamorfismo em fácies anfibolito, com expressiva formação de hornblenda, e alteração hidrotermal em condições de fácies xisto verde a sub-xisto verde, caracterizada pela formação de minerais hidratados (talco, serpentina, actinolita, tremolita e clorita). Texturas e estruturas primárias, como acamamento ígneo, do tipo rítmico, e textura cumulática, são ainda preservadas. Importantes ocorrências de blocos de minério maciço rico em Fe-Ti (± V) são encontradas, principalmente, no domínio das rochas metamáficas. Dados de geoquímica de solos indicam valores anômalos de S, Cu, Co, Ni, Ti e V, sugerindo a existência de alvos potenciais para sulfetos (Cu, Co e Ni) e óxidos (Ti e V).