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Resumo: O presente trabalho e um estudo petrografico das fases primarias e secundarias de uma rocha kamafugitica, intrusao nomeada Luz262, de um afloramento proximo a BR 262, nos arredores da cidade de Luz, no centro-oeste mineiro. A rocha e composta por olivina, parcialmente substituida por serpentina, clinopiroxenio, perovskita, flogopita, opacos, pseudomorfos de leucita (analcima), venulas de natrolita e material intersticial (vidro vulcânico/feldspatoide). A rocha apresenta xenolitos sedimentares de siltitos, compostos principalmente por ortoclasio, provenientes da Formacao Serra da Saudade; alem de autolitos constituidos basicamente por clinopiroxenio, perovskita, opacos, apatita, pseudomorfos de leucita e natrolita. A rocha foi classificada como leucita-mafurito com base na presenca limitada de leucita (cerca de 10% modal), alem da provavel presenca de kalsilita intersticial, como ja descrito anteriormente em rochas semelhantes do Grupo Mata da Corda, da Provincia Ignea do Alto Paranaiba. A partir de analises petrograficas por microscopio optico, mineralogicas por difratometria de raios-x e quimicas por microssonda eletronica foi determinado que os feldspatoides originalmente potassicos, sofreram um processo secundario de troca do K pelo Na, representado na substituicao de leucita e kalsilita por analcima. Palavras-chave: Kamafugito, petrografia, analcimizacao, Minas Gerais Abstract THE ANALCIMIZATION PROCESS OF A KAMAFUGITE (LUZ262) FROM THE MIDWEST OF MINAS GERAIS. The present paper is a petrographic study of the primary and secondary phases of a kamafugitic rock, intrusion named as Luz262, found in an outcrop nearby BR-262, nearby the town of Luz in the middle west of Minas Gerais. The kamafugite is composed by olivine partially replaced by serpentine, clinopyroxene, perovskite, flogopite, opaques, leucite pseudomorphs (analcime), veins of natrolite and interstitial material (volcanic glass/feldspathoid). The rock contains sedimentary xenoliths of siltite, mainly constituted of orthoclase from the Serra da Saudade Formation, as well as autoliths composed basically of clinopiroxene, perovskite, opaques, apatite, leucite pseudomorphs and natrolite. The rock is classified as leucite-mafurite based on the limited presence of leucite (around 10% modal), besides the probable presence of interstitial kalsilite, as previously described on similar rocks of the Mata da Corda Group from the Alto Paranaiba Province. By using petrographic analysis with optical microscope, mineralogical analysis by x-ray diffraction and chemical microanalysis with electron microprobe it was determined that the feldspathoids originally potassic, suffered a secondary change process of K by Na, with transformation of leucite and kalsilite to analcime. Keywords: Kamafugite, Petrography, Analcimization, Minas Gerais

O PROCESSO DE ANALCIMIZAÇÃO DE UM KAMAFUGITO (LUZ262) DO CENTRO-OESTE MINEIRO