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DISSOLUTION OF K-FELDSPAR INTO SI-AL GEL AND CRYSTALLIZATION OF HALLOYSITE IDENTIFIED IN THE KAOLIN DEPOSIT OF SÃO VICENTE DE PEREIRA (PORTUGAL)

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• Volume 51 No.1 / February 2000

Published: Feb 2000

Pages: 49 - 57

Authors: IULIU BOBOS, CELSO GOMES

Abstract: Dissolution of K-feldspar into Si-Al non-crystalline phase was identified in the kaolin deposit of São Vicente de Pereira (Portugal). The gel having a SiO₂/Al₂O₃ ratio approximately equal to the unity, crystallized into halloysite-0.7 nm. SEM investigations carried out on K-feldspar grains show a vacuolar texture characterized by etchpits of various dimensions. The pits exhibit various shapes, either polygonal or circular. The gel was identified by SEM on the K-feldspar surfaces and by TEM in the < 2 ωm clay fractions. TEM images display tubes of halloysite-0.7 nm surrounding flakes of Si-Al gel. Relicts of K-feldspar pseudomorphs submitted to amorphization are identified by TEM. SAED analyses confirmed the non-crystalline state of the gel. Electron microprobe analyses attested a very fast destabilization of the chemical structure of K-feldspar grains.

Keywords: Portugal, kaolin deposit, scanning and transmission electron microscopy, X-ray diffraction, K-feldspar dissolution, Si-Al gel, halloysite-0.7 nm

Volume 51 no. 1 / February 2000

• BILJANA MITROVIC, GORDANA JOVANOVIC

  QUATERNARY MALACOFAUNA OF TOPOLOVNIK AND GOLUBAC (NORTH-EASTERN SERBIA)

• SLAVOMIR NEHYBA

  THE CYCLICITY OF THE LOWER MIOCENE DEPOSITS OF THE SW PART OF THE CARPATHIAN FOREDEEP AS THE DEPOSITIONAL RESPONSE TO SEDIMENT SUPPLY AND SEA-LEVEL CHANGES

• MICHAL NEMCOK, PATRIK KONECNY, ONDREJ LEXA

  CALCULATIONS OF TECTONIC, MAGMATIC AND RESIDUAL STRESS IN THE STIAVNICA STRATOVOLCANO, WESTERN CARPATHIANS: IMPLICATIONS FOR MINERAL PRECIPITATION PATHS

• PETR SPACEK, JIRI KALVODA

  RECONSTRUCTION OF SYN- AND POSTSEDIMENTARY TECTONIC EVENTS IN FLYSCH BASIN FROM LIMESTONE PEBBLES VARIATION: DRAHANY CULM OF THE MORAVIAN RHENOHERCYNIAN ZONE

• IULIU BOBOS, CELSO GOMES

  DISSOLUTION OF K-FELDSPAR INTO SI-AL GEL AND CRYSTALLIZATION OF HALLOYSITE IDENTIFIED IN THE KAOLIN DEPOSIT OF SÃO VICENTE DE PEREIRA (PORTUGAL)

• MARIAN PUTIS, ALEXANDER B. KOTOV, PAVEL UHER, EKATHERINA B. SALNIKOVA, SERGEI P. KORIKOVSKY

  TRIASSIC AGE OF THE HRONCOK PRE-OROGENIC A-TYPE GRANITE RELATED TO CONTINENTAL RIFTING: A NEW RESULT OF U-Pb ISOTOPE DATING (WESTERN CARPATHIANS)