The cerite supergroup is established and includes the cerite group (silicates) and merrillite group (phosphates). Cerite-group minerals are cerite-(Ce), ferricerite-(La), aluminocerite-(Ce) and taipingite-(Ce). The merrillite group is subdivided into two subgroups: merrillite (merrillite, ferromerrillite, keplerite and matyhite) and whitlockite (whitlockite, strontiowhitlockite, wopmayite and hedegaardite). Cerite-(La) has been renamed ferricerite-(La). The new nomenclature has been approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification.
a b s t r a c tThe Ceramic District of Santa Gertrudes (CDSG) is the largest producer of ceramic floor and wall tiles in Brazil. Tile manufacturers in the CDSG use the single raw material, clayey rocks from the Corumbataí formation. Mineralogical, chemical, thermal and microstructural characterization of the clayey rocks from the Corumbataí formation have been performed in order to better understand effect of the studied properties on dry route tilemaking process. The results revealed different compositional features among the studied clayey raw materials. The bulk samples were dominated by clay minerals associated with quartz, feldspars and minor amount of hematite. All samples were complex mixtures where different types of clay minerals (illite, smectite, illite-smectite, kaolinite-smectite, chlorite, sometimes kaolinite) coexist in variable amount. The amount of clay minerals increased with a higher degree of weathering of studied samples. Different technological behavior was expected for studied raw materials due to their heterogeneous nature, in terms of mineral composition and weathering degree. To improve technological behavior of studied materials during tilemaking process an upgrade of the currently used raw materials preparation is recommended (raw materials maturation, more aggressive milling of raw materials, addition of plastic component and homogeneous mixing of plastic and non-plastic components).
A Formação Corumbataí na região de Rio Claro - Limeira - Araras é representada por uma sucessão de siltitos, constituídos principalmente por filossilicatos (predominando illita, embora também ocorram montmorillonita, biotita, clorita, caulinita e interestratificados regulares e irregulares, quartzo, plagioclásios e feldspatos potássicos, carbonatos, hematita, goethita e zeólitas, de origem autígena e/ou detrítica. Quimicamente as rochas da Formação Corumbataí são classificadas principalmente como wackes e secundariamente como folhelhos, cuja principal fonte são rochas ígneas félsicas e/ou rochas sedimentares quartzosas. A aplicação de índices de maturidade química nas rochas analisadas sugere que estas são quimicamente imaturas e que a fonte foi submetida a condições de intemperismo moderado. Diagramas discriminantes para ambientes tectônicos sugerem que a fonte dos sedimentos da Formação Corumbataí são rochas quimicamente semelhantes a rochas formadas em margem ativa e/ou arcos de ilha, embora depositados em outro contexto geotectônico (bacia intracratônica).
A B S T R A C TThe Ceramic District of Santa Gertrudes (CDSG) is the most important producer of ceramic floor and wall tiles in Brazil. Industries that produce ceramic tiles by dry route process have researched new technologies to dry the Corumbataí Formation (Fm) raw materials. It is due to environmental problem related to the dust emission in the air, produced by beneficiation areas where the raw ceramic materials have been dried. Laboratory experiment and technological test, simulating the current tile production processes in the CDSG, were performed in the present study in order to better understand the role of temperature on clayey rocks from Corumbataí (Fm) and to avoid losses in the current tile production process. Three different illitic raw materials of different degree of weathering and compactness (hard, intermediate and soft) already used to compose the ceramic batch were dried by sunlight and forced drying at 100°C, 200°C and 300°C. Results after forced drying have shown changes at the raw material morphology and size distribution after grinding; also the progressive dehydration of the expandable clay minerals which have caused the plasticity and consistency loss of the raw material and consequently affected the quality of the product. Ceramic bodies presented decreasing linear shrinkage values, loss in their bending strength, and horizontal cracks in some bodies whose raw materials were forced to dry at 200°C and 300°C.
Terrae Did atic a IntroduçãoA Cristalografia é uma ciência cheia de regras (convenções internacionais) que foram feitas para que pessoas do mundo todo usem as mesmas orientações cristalográficas e nomenclaturas, de modo a que possam se entender. Se cada um usasse regras diferentes para orientar os cristais e classificá-los, por exemplo, quanto ao grupo pontual, classe cristalina e sistema cristalino, a Cristalografia iria se tornar muito complexa. Estas questões não são, em geral, muito claras nos livros introdutórios de Cristalografia, como naqueles voltados para sua aplicação na Mineralogia, como Bloss (1971), Chvátal (2007 e Klein & Dutrow (2012). Por outro lado, as convenções atuais, padronizadas pela IUCr (International Union of Crystallography), são algumas vezes impróprias. Por exemplo, ao denominarem triclínico um sistema no qual não obrigatoriamente todos os ângulos da cela unitária são diferentes de 90°, ou ao denominarem monoclínicos cristais que podem ter ângulos todos iguais a 90°. FundamentaçãoAlgo que atrai muito a atenção nos cristais é a presença de faces planas. Estas faces podem se repetir algumas vezes, apresentando-se rotacionadas em relação umas as outras (são faces idênticas e podem ser vistas após uma rotação do cristal), ou podem estar refletidas (uma é a imagem espelhada da outra), ou invertidas (uma é o inverso da outra). Esta repetição é conhecida como simetria. Para descrever a simetria, podem ser utilizados alguns elementos fictícios, chamados de elementos de simetria, que nos permitem imaginar como as faces dos cristais se "reproduzem". Um deles é o eixo de simetria próprio, uma linha imaginária, ao redor da qual aparecem faces repetidas 2, 3, 4 ou 6 vezes. Outro elemento de simetria é o plano de simetria, que funciona como um espelho e faz com que as faces apareçam aos pares, sendo uma a imagem especular da outra. Um terceiro elemento é o centro de simetria, que, quando existente, fica no centro geométrico do cristal e faz com que para todas as faces apareça o seu ARTIGO http://dx.doi. org/10.20396/td.v13i3.8651222 ABSTRACT: Crystal systems are presented in crystallography introductory books according to the set of symmetry elements and with respect to the axial orientation. However, what is fundamental for the crystal system definition is only the symmetry elements set and not the axial orientation. Some of the names applied to crystal systems are actually connected to the symmetry elements: trigonal, tetragonal, and hexagonal. The other systems have names related to the axial orientation: cubic, orthorhombic, monoclinic, and triclinic. It seems logical to think that the triclinic crystals are those that have all angles different from 90 o and that the monoclinic crystals are those that present only one angle different of 90 o , which is not always the case. "Diclinic" crystals, with one angle equal to 90 o and two different, also exist, and are grouped with the triclinic ones, because they present the same crystal classes. The conventions for nomenclature of crystal systems c...
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