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mineralogy

Minerals discovered in Brazil

Compendium updates analyses and corrects mineralogy errors accumulated over centuries

A mineralogist at the Geosciences Institute of the University of São Paulo (IGc-USP) has solved the problems of nomenclature of Brazilian minerals, completing previous studies and categorizing all of the minerals first discovered here – in general by foreigners -, of the so-called typical minerals of Brazil. Daniel Atencio dedicated five years to collecting scattered pieces of information and to carrying out painstaking analysis, in order to produce the compendium Brazilian Mineralogy Recollection – his professor thesis of 1999.

Before 1959, when the International Mineralogy Association established a special commission in which professor Atencio represented Brazil, there were more than 100 minerals considered to have been discovered here – without taking into consideration the orthographic variations or attributions of various names to the one mineral. Following directives that the commission had laid down for the validation of names, the professor verified that around 80 minerals should be rejected – either because they were not really new or because the study didn’t have conclusive data. In this manner the Brazilian list was reduced to 39 minerals.

A lack of the basics
“This is a very small number”, he says “and certainly doesn’t correspond to the Brazilian mineral richness, which many compare to the United States and Russia.” Each one of these countries has more than 600 minerals described and throughout the world close to 4,000 have been discovered. This suggests that the Brazilian soil has been poorly explored – at least scientifically. The region of Poços de Caldas (MG), for example, is rich in nephelite syenite, an alkaline rock from which rare minerals such as zirconium develop. In Russia and Canada close to 200 minerals have been found in this type of rock, but in Brazil only 20.

Of the 39 minerals discovered in the country, 33 were discovered by foreigners. “The majority of students are only interested in applied research, but the application invariably depends on the information that can only be obtained though good basic work”, explains the professor who found out about the problem when he graduated in 1982. “The descriptions, some from previous centuries, were very erratic. Many things had been lost.” What was missing was an effort to compile the data. Once having decided to put some order into the situation, errors and omissions were discovered, since the majority of the work was from the 18th, 19th and early 20th centuries, when technology had not yet allowed for a refined analysis.

A fine piece of work was the rescue of scattered studies. The greater volume was sent by the Belgium Jacques Jedwab, of the University of Brussels. Rare studies, such as the original ones on palladium by William Hyde Wollaston (1766-1828) were found, as well as the work of Lampadius e Plattner in 1833 on Palladinite. Palladium is a metal found in Minas Gerais, in the form of opaque white to pale steely grey grains. The Palladinite is an oxide of palladium and copper in the form of grey grains.

Analytical errors
Errors were common because the analyses were carried out by the wet method: relatively large volumes of the minerals were dissolved, in a way that many times results didn’t refer to one only mineral, but to a mixture. Presently with the electronic microwave, it is possible to obtain chemical compositions for very small mineral areas.

One of the verified errors involves harbortite from the island of Trauíra (MA), described in 1932 by F. Brandt: on determining the composition of the mineral, the author had disregarded the sodium and designated it as a hydrated aluminum phosphate. Professor Atencio discovered a study partially lost in the Annuals of the 31st Brazilian Geology Congress (1980): “It was from the Brazilian researchers, Marcondes L. Costa et al., who had already proven that the mineral collected on the Trauíra Island was in fact a phosphate of aluminum and sodium – or that is to say, another mineral, already known as wardite.” As a result, the name Harbortite was dropped.

Chernikovite, which forms plates of a lime green color, was discovered by the Russian Andrey Chernikov (1927-), but was called Hydrogen Autunite. There was a second outcrop near the city of São Paulo in the district of Perus, in the form of rods that filled in cavities of tourmaline granite. Atencio’s analysis revealed that the mineral was not of the autunite group, but of the meta-autunite group, which contains (H3O)+ ions, and not simply H+ as had been believed. He renamed the mineral as Chernikovite, in honor of the Russian mineralogist.

A mineral collected in Poços de Caldas, and described in1948 by Djalma Guimarães (1894-1973), occurred in the form of crystals that filled the cavities of rocks was called Giannettite. Professor Atencio analyzed the crystalline structure by x-ray and carried out an updated chemical analysis using electronic microwaves: he discovered that he was dealing with hainite previously discovered in the Czech Republic in 1893.

Djalmaite – found in octahedrons, brownish-yellow, browish-greenish or dark-brown – was also described by Guimarães and in 1957 had its name changed to uranomicrolite. “It was described as a mineral of tantalum and uranium, but I discovered that its composition is very variable. Some samples are rich in lead, others in uranium, others in calcium etc.” The name uranomicrolite is not definite: it will depend on new analyses.

To find and prove errors, samples are needed, sometimes difficult to obtain, above all of minerals described when it was not an obligation to send them to a museum. In his search, Atencio obtained the largest crystals in the world of the so called mineral X of Perus: they are elongated tubular crystals of a bright yellow color. Described in 1965, they were not submitted to a quantitative chemical analysis because there was insufficient quantity. The conclusion of professor Atencio: mineral X was furcalite, which has already been described.

There are other reasons for searching out minerals in the States of São Paulo, Minas and Goiás: “I suspect that various minerals classed as rare are much more common than we think”, says the professor. The mineral Zanazziite, for example – olive green crystals in the form of bars or rosettes -, described in 1990, was registered as occurring only once on an island of the river Jequitinhonha in Itinga, in the north east of the State of Minas Gerais. Recently it was discovered in two other locations.

Ouro Preto (Black Gold) and Brazilianite
Professor Atencio tells some curious cases such as that of Ouro Preto( Black Gold). This curious metal like substance covered with a dark crust is a century old misunderstanding. It was so abundant in Vila Rica, that the authorities gave its name to the town. Described in 1711 by the Jesuit priest André João Antonil (1649-1716), who had been telling of the riches of Brazil to the Portuguese court, this was the oldest mineral to be described in the country. Until in 1995 it was unmasked through studies by Jacques Jedwab: we were dealing with a mixture of the oxides of iron, palladium, platinum, gold, copper and manganese.

This mixture of compounds cannot receive the name of a mineral because it is amorphous, or that is to say, it does not have a fixed crystalline structure – an essential condition in 99.9% of cases for classification as a mineral. Since its formula was incompatible with the standard definition of a mineral, Ouro Preto, as a mineral, was erased off the list. Consequently the position as the oldest mineral passed to that mineral described in 1789 by D.L.G. Karsten: chrysoberyl, of flat plates or short prism shaped crystals in various tones of green or yellow.

Another mistake was the result of an attempt to honor the country. In 1818, the name brazilianite was given to a fibrous mineral found in Córrego Carmo, between Ouro Preto and Mariana (MG). Afterwards it was discovered that they had been dealing with Gibbsite. Then in 1945, the name was meritoriously awarded to a valuable gem of yellow-greenish crystals, truly unprecedented, discovered in Divino das Laranjeiras (MG).

Beginning with his thesis-compendium, which is in the library of IGc-USP, professor Atencio prepared Mineralogy Type of Brazil, a book of some 114 pages published in 2000 by the Geosciences Museum of USP. Presently he is dedicating himself to a list of minerals without a determined crystalline structure or without a complete description. In the end, the list of minerals typical of Brazil needs to be extended.

The Project
Minerals Described for the First Time in Brazil and their Whereabouts (nº 96/00669-0); Modality Regular line of research support; Coordinator Daniel Atencio – Geosciences Institute of USP; Investment R$22,539.00 and US$ 26,156.77

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