ALTERATION MECHANISM OF BIOTITE IN GRANITIC ROCK CAUSED BY CRUSTOSE LICHEN "PORPIDIA"

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概要

• 論文の詳細を見る

• The alteration mechanism of biotite in granitic rock caused by crustose lichen "Porpidia" was investigated by means of X-ray diffraction, optical microscope, EPMA and electron microscope with EDX. Vertical thin sections of lichen-rock interface were observed by a scanning electron microscope to make clear the physico-chemical phenomenon caused by lichens. The contact surfaces between lichen and a biotite were physically observed with this section, and were further investigated chemically by EPMA. As a result, physical destruction of biotite grains by lichen thallus was observed, and the formation of iron oxide or hydroxide was recognized. The chemical compositions of some parts of the biotite crystal were analyzed by EPMA, such as altered parts closed to lichen thallus, altered parts far from lichen thallus and fresh parts. Consequently, comparison of the different parts revealed increase in SiO_2 content on one hand and decrease in FeO and K_2O on the other hand from the fresh biotite crystal throughout the lichenic alteration. Due to the lower solubility of SiO_2 and higher solubility of Fe_2O_3 and Al_2O_3 from minerals under strong acid condition, which is formed by lichen thallus, it seems that Si^<4+> content in tetrahedral site is increased by cation exchange. Also due to the low pH and activity of high molecular weight polymers, the possible weakening of the iron-oxygen bonds will lead to the dissolution of Fe^<3+> ions. Consequently, it is likely that, due to the increasing negative charge of biotite layers with dissolution of Fe^<3+>, dissolution of K^+ will be disturbed. Vermiculite-like minerals in biotite formed with the action or effect of lichen were identified by quantitative chemical analysis as wt% of oxides and calculation of structural formulae on the basis of 22 oxygen atoms per unit cell.

• 日本粘土学会の論文

著者

• KITAGAWA RYUJI

  Department of Earth and Planetary System Science, Hiroshima University

• Kitagawa Ryuji

  Department Of Earth And Planetary Sciences Graduate School Of Science Hiroshima University

• Watanabe Katsuaki

  Department Of Earth And Planetary Systems Science Graduate School Of Science Hiroshima University

• Kitagawa Ryuji

  Department Of Earth And Planetary Systems Science Graduate School Of Science Hiroshima University

• Watanabe Katsuaki

  Department Of Earth And Planetary Science Graduate School Of Science The University Of Tokyo

関連論文

• THE OCCURRENCE AND STRUCTURE OF VERMIFORM CHLORITE
• KAOLINIZATION OF SAPROLITE DEVELOPED ON PAN AFRICAN GRANITE OF BATIE DISTRICT, WEST PROVINCE OF CAMEROON
• MORPHOLOGICAL TRANSFORMATION OF KAOLIN MINERALS FROM GRANITE SAPROLITE IN THE WESTERN PART OF CAMEROON
• SURFACE MICROTOPOGRAPHIES OF PYROPHYLLITE FROM THE SHOKOZAN AREA, CHUGOKU PROVINCE, SOUTHWEST JAPAN
• ALTERATION MECHANISM OF BIOTITE IN GRANITIC ROCK CAUSED BY CRUSTOSE LICHEN "PORPIDIA"
• MINERALOGICAL CHARACTERIZATION OF ASIAN DUST COLLECTED IN FUKUOKA, SOUTHWEST JAPAN

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