地表条件下における花崗岩の人工変質 : 酸性雨の岩石鉱物に与える影響の研究 (その2)

概要

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An artificial chemical weathering of a polished plate of granite from Kitagi, Okayama Prefecture, Japan was conducted using a Soxhlet extraction apparatus with distilled water and HNO_3 solution of pH 4 at 50℃ for a different period of time up to 189 days. The granite was composed mainly of quartz, plagioclase (Ab_<86>An_<12>Or_2), alkali feldspar (Or_<92>Ab_8) and biotite. The results showed the release of elements and the degree of weathering of minerals as a function of leaching time. Among the all minerals, biotite showed the higher chemical weathering that was enhanced by the HNO_3 solution. The chemistry of the surface of each mineral shows a characteristic change during the chemical weathering as follows : 1) The ratios (Mg+Fe+Mn+Cr) / Al in the octahedral sheet and (K+Na+Ca) / (Total Al) in the interlayer of biotite decrease with the increase of leaching time, but the ratio (Si+Ti) / Al in the tetrahedral sheet is not changed ; 2) The tatio (Na+Ca+K) / Al for plagioclase decreases with the increase of leaching time. Smectite, containing a small amount of iron, was developed from the alteration of plagioclase during the chemical weathering by the HNO_3 solution.
日本粘土学会の論文
1993-08-31