Boletim da Faculdade de Filosofia, Ciências e Letras da Universidade de São Paulo. Mineralogia
Boletim. Mineralogia - Faculdade de Filosofia, Ciências e Letras, Universidade de São Paulo
Universidade de São Paulo. Faculdade de Filosofia, Letras e Ciências Humanas
Petrologia da Região de São Roque, São Paulo
This paper is concerned with São Roque series in the vicinity of the city of São Roque in the State of São Paulo. Pre-Cambrian para-metamorphic rocks form this series. However, many of the more prominent outcrops consist of "Pirituba" granite types formed by large phenocrysts of microcline in a coarse ground mass which are intrusive in the country rocks and, consequently, of later age. These granites are generally supposed to belong to the Pre-Devonian. Tectonic 1) The "granites" (field term which includes: granites, adamellites and granodiorites) show plane-fluidal structures because of upward fluxional movements, during the period in which the physical state of the magma was still plastic or semiplastic. Their structures demonstrate discordant contacts between batholith and country rocks. The flow layers seem to form gentle folds. Their axes are approximately coincident with the horizontal axis of the batholith and, locally, with NE-SW contact: "granite" — limestone. 2) It lacks macroscopic evidence of lineation in the intrusive rocks. 3) The aplitic and pegmatitic formations of the batholith took place only along joints trending 70° NE and dipping steeply northward. Elsewhere in the country rocks aplites and pegmatites are found in the direction of the rock bedding. 4) There are other planes of possible faulted marginal joints in the batholith. The fault observed seems to have taken place much later than the magma consolidation and due, perhaps, to a quite recent regional diastrophism which, by the same way, has also affected the country rocks. 5) The tectonic characteristics of the area seem to show an active intrusion of the magma, which has by this way deformed somehow the country rocks. 6) On the last stages of the chamber-forming process, the magma should have ejected great number of apophyses and dikes which have separated blocks of the country rocks by piecemeal-stoping. Petrography of the igneous rocks. 1) The plutonites found in the area are typical adamellites and granodiorites, according to Johanssen s classification. 2) The sequence of crystallization is the following: magnetite, apatite, epidote, titaniL e, hornblende, biotite, plagioclase, potash feldspar and quartz. 3) Cases of hydrothermal metasomatic alterations were observed in the plutonic rocks. The principal observed modifications were: chloritization and epidotization of the femic minerals; decalcification of the plagioclase and increasing amount of quartz in the rock. 4) In three different observed localities the rocks show appreciable variation in mineral quantities and the plagioclases become more basic. 5) Cataclastic and milonitic textures, as a result of dynamo-metamorphism, take place on the batholithic boundaries along inner faults and in intrusive bodies in the country rocks. 6) Magmatic differentiation of the pegmatite stages includes: pegmatite, pink aplite and purple turmaliniferous aplite. The latter was partially formed before the other two. 7) There are several types of milonitized rocks inside the granitic batholith. The type showing the most intensive cataclastic effects is the so called ultra-milonite, very common in the quarry of the Sorocabana Railway near Sao Roque, which forms pseudo-dikes along the faults. 8) Deposition of hydrothermal minerals through the milonitized faults was observed. Petrography of the xenoliths 1) Two xenoliths found in batholithic boundaries show a calcareous origin. 2) The above mentioned xenoliths were not reabsorbed because of chemical exchange between them and the magma. The xenoliths have provided the magma with a part of the CaO, all of the C02 and possibly of some of the MgO. In the other hand the magma has introduced in the xenolith: SiO.,; Alr,0H; FeO; Fe2Oa and NaoO. The xenolith rock becomes a granular silicatic aggregate where the conspicuous minerals are diopsidc and oligoclase. Petrographic development of the granitic magma. 1) The magmatic orign of the rocks can be seen by their lithological characteristics and their geological relations to the country rocks. 2) Some chemical and mineralogical aspects exhibited by the xenoliths show that the limestone were assimilated by the magma. 3) Daly's hipol hesis of magmatic sloping would explain such a assimilation process. 4) The granitic rock was submitted in some places to a hydrol hermal alteration after the consolidation and after, at least, two cataclastic movements. Metamorphism 1) The limestone, the only rock here studied petrologically, shows the effects of two kinds of metamorphism: dynamo-thermal or regional metamorphism and contactmetamorphism. 2) The regional metamorphism provoked recrystallization, formation of silicates, stress, folding and lifting of the layers. 3) The limestone should be placed at the Tilley's "chlorite zone" because it shows a comparative low degree of metamorphism. Meanwhile, it was observed the formation of diopside, a mineral of more intense metamorphism. It is believed that it was formed during the regional metamorphism. This mineral was not in equilibrium with the other minerals of the rock. A reasonable explanation to this phenomenon is found in the initial chemical composition of the layer, sometimes containing diopside, or by the absence of stress on the same bed. 4) Zones of calcic-silicate hornfels contiguous to the batholith proves the existence of contact-metamorphism. 5) The. contact-metamorphism took place by a process of addition and not by recombinative crystallizations since the hornfels observed in three different outcrops have shown reasonable amount of feldspars. Away from the contact zone there was not observed neither those minerals nor others that could explain their origin. 6) The addition of substances by the magma to the country rock is also suggested by comparing chemical analyses of samples of rocks sucessively more distant from the contact. 7) The addition of substances were made possible by means of magmatic residual solutions of approximately pegmatitic chemical composition that had impregnated and metasomatized the limestone. The effects were more intensive in the contact "hornfels" but it is possible also that the solutions could have affected some beds originally more quartzoses and pervious more distant from the intrusion.
Direitos autorais (c) 2016 Boletim. Mineralogia - Faculdade de Filosofia, Ciências e Letras, Universidade de São Paulo
Contribuição à Geologia da Bacia de Taubaté - Vale do Paraíba - Estado de São Paulo
Tese de Doutoramento apresentada à Faculdade de Filosofia, Letras e Ciências da Universidade de São Paulo
Estudo Mineralógico de Argilas do maciço alcalino de Poços de Caldas
Contribuição ao estudo da influência de radiações ionizantes sobre a côr da Turmalina
O Autor procurou verificar os efeitos relacionados com a côr da turmalina através de irradiações com raios gama e com nêutrons produzidos no reator (IEA — RI) do tipo piscina, de 5 Mw. do Instituto de Energia Atômica, Universidade de São Paulo. Suas observações foram levadas a efeito com turmalinas de coloração rosa, vermelha, verde e azul de diferentes procedências, tôdas do Estado de Minas Gerais. Os resultados de suas observações constam ainda de 15 gráficos correspondentes aos espectros de absorção e de fotografias, apresentadas no trabalho, onde são consignados os efeitos de bombardeamento e, por vezes, os relacionados com posteriores tratamentos térmicos. São também registrados no trabalho observações relacionadas com o tratamento térmico de turmalinas não irradiadas artificialmente, onde o efeito só é notável no que concerne amostras de coloração rosa ou vermelha. Outras observações foram realizadas em turmalinas bicolores exibindo estrutura zonada rosa e verde claro paralela ao pédio basal e estrutura zonada vermelho e verde claro paralela às faces de prisma. Foi ainda observado o comportamento de pedras lapidadas em relação às radiações ionizantes onde verificada a intensificação da tonaldade das turmalinas rosa em função do volume da pedra e do tempo de exposição ao reator Verifica o Autor que a influência dos raios gama é desprezível afetando apenas ligeiramente as turmalinas de côr rosa e vermelha; que a influência de nêutrons é marcada, sendo mais sensivel nas turmalinas mais claras, especialmente nas rosa e vermelha. A tonalidade dessas turmalinas aumenta progressivamente até que, após exposição prolongada, atinge coloração castanho. As turmalinas verdes e azuis mantém suas cores que só se modificam nitidamente quando irradiadas por tempo relativamente grande, quando assumem coloração castanho, embora de tonalidade pouco diversa entre si e diversa das que resultaram de bombardeamento de amostras rosa e vermelhas. Verifica, entretanto, que nas zonas verde muito claro dos exemplares bicolores estudados, o efeito de tratamento com nêutrons pode se traduzir por sensível alteração de cor que pode variar do vermelho ao castanho na razão direta da maior intensidade da coloração verde. No que tange o tratamento térmico sobre turmalinas não irradiadas verifica que só são nitidamente afetadas as turmalinas vermelhas e rosa que, dependendo da temperatura, podem ficar incolores. Em relação ao mesmo tratamento realizado com pedras previamente bombardeadas o mesmo fato pode ocorrer com os exemplares que na fase de pré-irradiação apresentavam cores rosa e vermelha. As verdes e azuis que por radiação ionizante enérgica assumiram coloração castanho, readquiriram, por aquecimento, suas cores originais. Conclui o Autor que a cor das turmalinas estudadas pode não depender de um a só causa agindo isoladamente e que esta pode depender de fenômenos químicos ou físicos ou da associação de ambos; que as côres verde e azul parecem depender exclusivamente de isomorfismo ao passo que as rosa e vermelha parecem depender precipuamente de radioatividade natural e ainda ser possível que a cor de turmalinas e a de outros minerais alocromáticos de procedências diferentes dependa de fator ou fatores diversos. A credita o Autor que a cor das turmalinas rosa e vermelha esteja ligada a centros-de-coloração, admitindo ser possível que o Li tome parte na formação desses centros. Julga ainda que, admitida a origem radioativa dessas côres, medidas as intensidades relativas, ser possível estimar a quantidade de radioatividade externa e, talvez, o seu tempo de ação
O Gnaisse alcalino de Serra do Matola - São Jõao Del Rei
This paper deals wTh the so-called Serra do Matola alkaligneiss, emphasizing its geologic and pétrographie characters. This alkaline formation situated south of São João Del Rei, Minas G era’s, Brazil has a N-S elongated shape, with a length of about 20 km and an area of 100 km 2, approximately The bed rock outcrops in small areas totaling 20.000 m2, mainly in the escarpments facing north. Bounding the alkali-gneiss sierra, one can find charnockit ’c gneisses to the east and the Piedade biotite-gneiss to the west both of which can be inferred to contact each other underneath the alkali-gneiss. The planar structure as well as contacts between alkali gneisses and biotite gneisses are sub horizontal and somewhat irregular, but the general dip is to the south. A sometimes strong lineation can be observed in the alkali gneiss trending around 24°W and plunging 8°S. In this formation, field evidences indicate EW movements but there are also subordinate thrust faults SN. A system of vertical shearing planes runs NE-SW and NW-SE. The charnockites are much more irregular and seem structurally independent from the alkali and biotite-gneiss. The general characters of the alkah-gneisses are: 1) undeformed, fine-grained, leucocratic; mafic minerals concentrated in dark zones, here called “shonkinitic gneiss”; 2) granular quartz in strings or scattered. Porphyroblasts of feldspar, aegirite-augite and titanite. Potassic feldspar: microcline (Ab20) showing variable perfection of grid twinning, probably related to the variable reticular obliquity, which in turn would be related to the temperature of its formation (always below 5f00°C). Plagioclase is albite (An7) seldom twinned and never zonned, indicating total metamorphic re crystallization. Piroxene: aegirite-augite averaging 10% of the Na molecule. Amphibole: hastingsite. Common accessories: titanite, magnetite, apatite, epidote, allanite and calcite. Biotite, zircon and andradite are very scarse. Allanite, which is responsable for the radioactivity in the gneiss, may be found partially metamictized: it sometimes substitutes for titanite or envelops apatite. The average content of T h 0 2 in the rock is 0.015%, but allanite — and consequently T h 0 2 — may be abnormally concentrated in certain melanocratic (shonkinitic) levels. 3) Both the chemical analysis and the chemical variation diagram of the rock show similarities to correspondent data for rocks considered as final products of magmatic differentiation, namely trachytes and alkali rhyolites (pantellerites). On this basis, the alkali gneiss is believed to be the product of regional metamorphism acting upon an alkaline efusive rock. The melanocratic layers may have come from basic differentiated magmas also m etam orphised. Regional metamorphism affected the alkali gneiss which was stabilized in the same facies and sub-facies of the biotite gneiss (see b elo w ). The N-S structural lines are believed to be due — as the petrofabric analyses suggests r— to tectonic movements along an E-W direction with probable WE transport. The klkaline magma may have crystallized at high temperature, bringing about homogeneous Na-K feldspars. The metamorphism is believed to have promoted the unmixing of the Or and Ab molecules, shown now as indepent crystals in the fine grained m atrix and as perthitic porphyroblasts. A t the same time the sodic pyroxene would turn to hastingsite. The general characters in the Piedade biotite-gneiss are: 1 — Undeformed fine to medium grained mesocratic rock, rich of biotite in preferred orientation. Pegmatitic venulation, microcline porphyroblasts and metamorphic layering are observed in places. Recrystallization is widespread but here and there a psammitic relict texture can be guessed. 2 — The plagioclase is the commonest mineral. It is unzonnsd and is scarsely twinned but shows a somewhat variable An content from sample to sam ple. A calculated average gives A n2i. Quartz, very much abundant here, and microcline, are closely comparable to their counterparts in the alkali gneiss. Lepidoblastic biotite is to be found in any thin section. Other minerals present include: muscovite, epidote, titanite, magnetite, apatite, zircon and garnet. 3 — Chemically the rock is comparable to the series granite-diorite or arkose-grayw acke. Taking into account the texture it is supposed that it evolved from a clastic graywackic sediment. Mineralogic analysis show that it was stabilized in the staurolite-almandine or kyanite-almandine-muscovite subfacies of the almandine amphibolite facies. The petrofabric simmetry analysis parallels those obtained in the study of the alkali gneiss, i.e. the N-S macro and microlineation would be due to a E-W movement. The general characters in the charnockitic rocks are: 1 — Dark, basic, medium grained, and entirely recrystallized rocks are represented by amphibolites and pyroxene-granu lites. Lighter colored, acid, coarse grained, essentially quartz feldspathic rocks are here called acid chamockites. There are intermediate types. 2 — The acid charnockites are made up of quartz, abundant orthoclase perthite and oligoclase antiperthite, hypersthene, diopside and some biotite. Pyroxene-granulites contain andesine or bytownite, hypersthene and diopside. Amphibolites are characterized by the andesine-hornblende association, the last mineral being the greenish brown variety relatively oxydised and anhydrous. In the amphibolites some red biotite and /or garnet may have formed by retrom etam orphism . No titanite or sphene were seen in thin-sections. There is a simpathetic relation in the Fe content between the two pyroxenes present in the charnockite series of rocks. 3 — The acid charnockites seem to have been palingenetically mobilized magmas. The pyroxene-granulites and amphibolites could well represent supra crustal rocks led to plu tonic environment, where they were metamorphised in the two sub-facies (hornblende-, pyroxene-) of the granulite facies. A previous author stated that the region in study was subjected to a SN thrust tectonism. This conclusion is not invalidated by the present author but it is suggested that the thrusts moved large sheets of hard rocks carrying the printed fabric imposed by an earlier dynamic phase. Mineralogical radiometric analysis were carried on concentrated sam ples. It was concluded that the mineral responsable for the radioactivity in the sane gne’ss is allanite and in the residual so’l mantle, an amorphous thorogumite
Contribuição ao conhecimento de rochas termometanórficas da série S. Roque
Minute am ethystine crystals of lanthanite w ere found covering fissure, surfaces of carbonate concretions in sedimentary pleistocene rocks at Curitiba, State of Paraná. The crystals show platy (001) habit, bounded by very narrow (100) (010) (110) and (111) faces. B esides m icaceous (001) cleavage,, tw o other parting (? ) directions w ere also observed. The crystals are invariably twinned according to (110) plane. Four pairs cross groups are common. Optical data are given . Some amount of rare earths of the cerium group m ay have been concentrated into ashes through prolonged plant decay. The lanthanite crystals would be the result of extration of lanthanum from ionic soil solutions, fixation on the surfaces of som e colloidal body (p silom elane in case) and final crystallization
Sôbre uma rocha com Escapolita de Acopiára Estado do Ceara
O autor descreve e analisa exemplar de rocha calco-silicática da região de Acopiára, Estado do Ceará. Os constituintes principais: diopsidio, feldspatos, yj-zoisita apresentam-se em boa parte substituídos por escapolita. Em bora o autor não tenha feito observações “in situ” deduz, pela presença na região de Acopiára de calcários, dolomitos e rochas commagnesita, que a rocha escapolitizaca originou-se em conseqüência de fenômenos de metamorfismo termal e metassomático
Apreciação Geológica e Petrográfica de algumas rochas básicas de Santos
In the present paper the authors present some data on the geology of Santos considering particularly the occurrences of basic rocks. The geologic map shows the main occurrences of these rocks, indicating their respective geologic coordinates. A rather detailed petrographic study of rocks, sampled at the occurences of São Vicente and ilha Porchat, revealed that the first one was a lam prophyric dike with a high percentage of olivine whereas the rock of the ilha Porchat was classified as diabase. It is the opinion of the authors that these occurrences originated at different geologic times, and that the olivinic rocks of São Vicente, whose origin is likely to be connected with the epeirogenic movem ents of the serra do mar, are younger than the diabase of the ilha Porchat
Arsenopirita de Juca Vieira, Caeté, Minas Gerais, Brasil
Well-formed arsenopyrite crystals occur included into sericite talc schists, associated with pyrite. The arsenopyrite, commonly twinned after (101) and (110) , shows the following crystallographic forms: (110) , (014 ) and more rarely (001) and (011) . The arsenopyrite is frequently fractured, exhibiting inclusions of euhedral pyrite crystals, which probably have been formed through replacement by penetration of forming solutions into the arsenopyrite small cracks
Aplicações da Trigonometria Esférica em problemas da Simetria Cristalográfica
The present article deals with the application of elementary spherical trigonometry to solution of symmetry problems. The main purpose of the article is to point out symmetry axis associations, and to show the possibilities and impossibilities of several associations, revealed through spherical trigonometric relations. The following axis associations have been a matter of study : a ) 6 + 6; b ) 4 + 4; c ) 2 + 2; d ) 6 + 3; e ) 6 + 4; f ) 6 + 2; g ) 4 + 3. For solution of all the proposed problem sonly one trigonometric formula has been used: cos a = cos b cos c + sen b sen c cos A which is applicable to scalene triangles
Contribuição ao conhecimento de Estruturas Migmatíticas no Complexo Brasileiro
It is the purpose of this paper to present briefly the results of a study of the genetic relations of the migmatite structures- of the area named Praia do Tombo, ilha Santo Amaro, State of São Paulo, Brazil. The migmatites in the area in question present the following petrographic features: the old rock, a biotite-hornblende gneiss, was intruded by granitic material whose main constituent is microclne. The illustrations give an idea of forming process. Pegmatite dikes cutting through the migmatite rock has provoked the formation of a characteristic greisening zone by a process of metasomatic alteration
Meta-Conglomerado e rochas associadas no Município de São Paulo
Determinação de Indices de Zona no Sistema Hexagonal
A general graphical solution of zone index determination in the hexagonal system is herein described. Zone axis may be treated as vectors in such a manner that they could be solved into several components, according to the crystallographic axis X, Y, W , Z. These components are proportional to the searched zone indices. The vector decomposition may be performed by drawing normals to the crystallographic axis from any given point P of the vector. In such way, the computed zone indices will satisfy the condition u+v +ɯ=0
Zeólitas dos Basaltos do Brasil Meridional (Gênese e Pagênese)
The basalts and diabases w hich cover an extensive area of the southern States of Brazil are of ten bearers of varied species of zeolites (analcite, chabazite, thomsonite, ptiloli"e, natrolite, scolecite, mesolite, laum ontite, stilbite, stellerite, and heulandite) and as m any other related minerals (delessite, daphnite, celadonite, quartz, chalcedony, calcite, gyroli"e, apophyllite, pyrite, and native copper). In the basalts the above m entioned m inerals occur in cavities of varied forms, w hile in the diabases they are located in the zones of shearing. They originated, mainly, from final residual solutions of the basaltic magm a itself, which were trapped inside the cavities or in the fractures of the diabases. The order of deposi'ion of the m inerals in the am ygdalae and fractures is no" haphazard. On the contrary, there exists a definite sequence, alw ays repeated, in the material examined, no matter what its source. The minerals of the chlorite group and those of the silica group are always the first to be form ed. They are follow ed by the zeolites, then apophyllite, calcite and fin ally the sulphides. Among the zeolites there is also a certain order of deposition. The heulandite precedes the rest. It is follow ed by stilbite, which in i"s turn precedes chabazite. In the zones of shearing of the diabases calcite seems to go contrary to the above order, preceding the deposition of zeolites. There are zones of amygdaloidal basalts in which the cavities are fille d by only one kind of mineral — sometimes only m inerals of the silica group, odier times only analcite, mesolite, or chabazite. Phenomena of pseudomorphic substitutions among the minerals which fill the cavities and fractures of the basalts and diabases are not rare. The inclusions of sandstones and even sands of the Botucatu form ation in the basaltic lava flows did not at all influence the lava which reached the surface. Th ere are no signs of thermal metamorphism between the oldest amygdaloidal basalts and lavas and the most recent diabasic intrusions. The absence of numerous species of zeolites seems to be connected witi the lack of certain elements in the lava and basalts and also the non-existence of differentiated pétrographie types. In the am ygdaloidal basalts, as well as in the homogenous ones and in the other types, as well as in the diabases there are found neither pyrogenic zeolites nor phenomena of analcitization
Estudos sobre as propriedades químicas dos Minerais de Zirconio da Região de Poços de Caldas — Minas Gerais
O conteúdo em háfnio dos minérios de zircônio da região de Poços de Caldas é baixo, em média aproximadamente 1,8% no total de zircônio e háfnia presentes. Em algumas zirconitas é, porém, menor, e parece que algumas amostras apresentam teôr mais elevado. As diferenças observadas são maiores do que o êrro experimental provável. É possí¬ vel obter frações mais ricas em háfnio por precipitação fracionada dos fosfatos em meio ácido sulfúrico na presença de bissulfato de sódio; obtém-se assim precipitados bem filtráveis, isentos de ferro e titânio. Embora seja reduzido o interesse da indústria na obtenção de háfnio, êste método tem possibilidades de êxito comercial uma vez que permite com algumas precipitações fracionadas obter-se uma solução rica em zircônio e praticamente isenta de háfnio. É, todavia, apropriado para a determinação analítica do háfnio em amostras que contêm pequenas quantidades deste elemento. A determinação qualitativa pode ser efetuada, com aproximação aceitável, pela precipitação dos pirofosfatos de zircônio e háfnio, em meio ácido clorídrico, por pirofosfatos de sódio e a n á¬ lise dos precipitados obtidos, depois de sêcos e calcinados
On the Chalcopyrite inclusions in Sphalerite
Uma das finalidades do presente trabalho foi medir as porcentagens de inclusões de calcopirita em cristais de esfalerita, que formam concrescimento de ocorrência relativamente frequente nas jazidas hidrotermais. Parece existir uma relação entre porcentagens de inclusões e intensidade hidrotermal dos depósitos, como também entre porcentagens de inclusões e variedades de esfalerita. Depósitos de baixa temperatura mostram porcentagens de 1-2%, enquanto aqueles de alta temperatura apresentam 5-6%. As inclusões de calcopirita geralmente ocorrem: a) nos pianos de clivagem (110) da esfalerita; b) nas superfícies de contato dos gemi nados de esfalerita; c) nos contornos dos cristais de esfalerita; e d) nas fraturas subsequentes da esfalerita. Experiências de corrosão das secções polidas com ácidos (etching) revelaram a textura dos agregados de esfalerita. As mesmas experiências tiveram pequeno efeito sobre a calcopirita. Água régia e ácido nítrico se mostraram como os melhores e mais satisfatórios reagentes. As investigações por meio de raios X foram levadas a efeito principalmente pelo método de rotação. As roentgeno-fotografias revelaram a orientação das inclusões de calcopirita em relação à estrutura reticular interna da esfalerita. Nas amostras estudadas a direção [100] da esfalerita parece ser paralela à direção [130] da calcopirita. Foram observadas inclusões de cristais dendríticos de esfalerita em alguns espécimes de calcopirita. O fenômeno da exsolução parece ser a explicação mais provável para as inclusões de calcopirita. As diversas evidências que serão indicadas abaixo comprovam este fato. Na introdução deste trabalho foi mencionada a controvérsia que existe entre Autores e estudiosos do assunto, sobre o problema das inclusões de calcopirita em esfalerita, isto é, se elas constituem o resultado de um processo de exsolução ou de substituição. Os dados obtidos para a elaboração do trabalho, sugerem a possibilidade da existência dos dois processos. Entretanto, a maioria das inclusões e grânulos de calcopirita situados no contorno de cristais de esfalerita parecem ser produtos de exsolução, enquanto a calcopirita “exterior” provavelmente se originou por substituição. Na grande maioria dos casos estudados a exsolução constitui o processo dominante. São enumeradas a seguir várias provas que falam em favor do fenômeno da exsolução: a. Texturas muito semelhantes observadas em ligas metálicas e conhecidas como produtos de exsolução. Exemplo comum é a exsolução de cementita de ferro metaálico, afim de formar pearlita. b. Semelhança de estrutura cristalina dos dois minerais: a esfalerita é monométrica com a() = 5,41 A e a calcopirita é tetragonal. Entretanto, esta pode ser considerada monométrica, em termos de substituição, pois as constantes de sua cela unitária são muito semelhantes às da esfalerita. As constantes reticulares da calcopirita são segundo Pauling e Brockway a() = 5,24 A e c0/ 2 = 5,15 A. Pequena diferença entre os diâmetros atômicos dos elementos metálicos considerados: cobre, ferro e zinco. Estes elementos se substituem reciprocamente, o que é evidenciado pela ocorrência de diversas variedades de esfalerita. Também, análises espectrográficas de esfalerita, provam que este mineral pode conter átomos de ferro e cobre em forma de solução sólida. Análises químicas revelam até 26% de Fe em algumas variedades de esfalerita. d. Pequena porcentagem de inclusões na esfalerita. As porcentagens nunca excedem 13%, mesmo nos depósitos de alta temperatura. e. Variabilidade das porcentagens de inclusões de calcopirita de acordo com a intensidade dos depósitos hidrotermais e de acordo com a variedade de esfalerita. f. Variabilidade do tamanho das partículas de calcopirita incluí¬das, de acordo com a intensidade do depósito e de acordo com a localização das inclusões no cristal de esfalerita. g. Zoneamento das inclusões nos cristais de esfalerita. h. Variabilidade das porcentagens dentro de cada cristal de esfalerita, pois frequentemente é maior no centro do cristal. i. Nã o conexão das inclusões de calcopirita com as partes exteriores do cristal, o que favorece a hipótese de que elas provavelmente se originaram no interior do próprio cristal de esfalerita. j. Duas gerações de calcopirita. K. Arranjo ordenado das inclusões de calcopirita dentro da estrutura reticular da esfalerita, determinada com auxílio de raios X. 1. Inclusões dendríticas de esfalerita em calcopirita. m. Ausência de calcopirita em algumas variedades de esfalerita, principalmente nas variedades claras
Minerais de Zircônio na Região de Poços de Caldas, Minas Gerais
Sôbre um Topázio de Arassuaí (Minas Gerais)
Morfologia da Wulfenita de Itapirapuan, São Paulo
Sôbre a Gênese de uma Jazida de Molibdenita do Rio Grande do Sul
Nota sobre a calcita de Pedra do Sino, Estado de Minas Gerais
Perfect translucent to transparent crystals of calcite occur in limestone at Pedra do Sino, State of Minas Gerais, Brazil. Habit of crystals are rhomboedral and scalenohedral predominantly as shown in the figures 1 and 2
Nota sobre a Baritina de Serrote, Estado de São Paulo
Crystals commonly tabular || c (001) occur in the place named Serrote (State of Sao Paulo) They are frequently found in the cavities of massive barite, which owes its origin probably to metasomatic processes. Occasionally the crystals exhibit distinct inclusion of microscopic needles of pyrolusite arranged in radiated orientation. Colourless when pure; yellowish and pale green
Arroja dita, um novo mineral do grupo da Wagnerita
Arrojadite occurs in pegmatites in the gneisses of Serra Branca, near Pedra Lavrada, Picui, Paraiba do Norte. A sample of the analyzed material presents in cleavable massive forms of deep green colour and natural faces were not found in the studied samples. Hardness over 5. It often encloses minute crystals of hematite and quartz. Inclusions of euhedral crystals of cassiterite are fairly common. It also shows abundant inclusions surrounded by pleochroic haloes. The following analysis of a sample with little amount of inclusions shows the relation between Arrojadite and inclusions: Cassiterite 0,61 per cent Hematite 1,29 Arrojadite 98,10 100,00 per cent Arrojadite alters to a dark red mineral which probably is monoclinic. Its index of refraction and birefringence are higher than that of Arrojadite. The alteration sets in from the exterior of the crystal and from the cleavage craks. This is a common alteration and the product of it is a biaxial mineral, optically positive (+ ), vellow, and grayish when in thin sections. 2V r = 16° The indexes of refraction are moderately high: Y = 1,724 p = 1,703 ( ± 0,001), a = 1,703 ( ± 0,001) Birefringence o Y-a = 0,021, Y-p = 0,0205, fl-a = 0,0004 In thin sections it is yellow with m a rk e d pleochroism Z = d a rk red, Y = orange yellow, X = brilliant yellow The maximum extinction angle in sections parallel to the cleavage planes is about 2° 15’ The crystallographic characters of arrojadite are: monoclinic, cleavage parallel to (110) is generally highly developped, and the plane of the optic axes is parallel to the cleavage planes. The relations between cleavage planes and crystallographic axes are shown in fig. 1. Optically, A rrojadite is negative (— ) Axial plane parallel to (110); 2 Vr = 82° The index of refraction is moderately high y = 1,657. Double refraction low: Y-« = 0,0079, Y - P — 0,0034, P - a = 0,0045. In thin section colourless, or faintly pleochroic: Z = pale green Y = incolour X = incolour Regarding chemical composition Arrojadite seems to be the same kind from Black Hills, South Dakota, which was described by W.P Headden in the American Journal of Science (1). This mineral and Arrojadite show the same megascopic features. The analyses shown at the pag. 8 give us an idea about the resemblance of these two minerals. The presence of F e 20 3 in the I and 11 analyses is due the that the samples analyzed h ad 2 to 3 per cent of hematite. The higher percentage of H20 is due to the alteration of the Arrojadite. Beside, the author gives a detailed discussion on the question of the priority of the name Arrojadite based, chiefly, on B. Masons works published in the Geologiska Forenniges I Stockholm Forhandlinger, of March-April 1941. This latter author ends by giving the priority to the name Arrojadite over the name Headdenita of Quensel. The author proposed the name Arrojadite to the inoxidized m ineral, which represents, when pure, the Headden’s phosphate from Black Hills, South Dakota, U.S.A
Nota sobre o crisoberilo de Santa Tereza
Chrysoberyl occurs in the place named Santa Thereza (State of Espirito Santo) in veins of pegmatite. The samples analysed are perfect: one of a single crystal is emeraldgreen and nearly about one centimeter in its larger dimension
The “Coromandel” diamond proceeds from the city of Coromandel, source of other large and well-known brazilians diamonds. It presents octaedric “habitus” with two natural and five clivage faces. It also shows a cube face. Dimensions according to the cristallographic axis, are: 53,00 mm; 39,00 mm; 26,60 mm. Weight: 400,65 metrics carats, a little less than Premier 5.° (South Africa) Color extremely-slight, without flairs which could decrease its value. Microphotographic pictures were taken from the rhombic figures of clivage