무등산지역에서 산출되는 화산암은 화순안산암, 무등산데사이트, 도곡유문암으로 구성되며 이들 화산암류는 공통적으로 사장석 반정을 포함하고 있다. 광학현미경 하에서 관찰된 사장석의 반복 쌍정 중 대부분은 알바이트 쌍정이며 일부가 페리클라인 쌍정을 보인다. 사장석들은 EPMA 분석 결과 화순안산암은 Ca 함량이 많은 안데신에, 무등산데사이트는 안데신에서 을리고클레이스에, 그리고 도곡유문암은 거의 순수한 알바이트에 해당한다. 광학현미경 하에서 판단이 어려운 알바이트와 페리클라인 쌍정은 전자현미경의 회절도형에서 쉽게 구분할 수 있다. 연구지역의 화산암에서 산출되는 사장석은 중간조성의 사장석이지만 빠른 냉각속도에 의해 생성되었기 때문에 상분리가 일어나지 않아[100] 방향의 전자회절도형에서 e-reflection이 나타나지 않는 것으로 사료된다.

Dissolution experiments were conducted to understand chemical nature of weathering of anorthosite from the Hadong area. Anorthosite and plagioclase from it were reacted with HCl or KOH solutions under various conditions concerning such as grain size, initial pH of solutions, and shaking Average composition of plagioclase used in the experiment was Na0.32Ca0.71Al1.71Si2.28O8.Under acidic conditions, solution pH increases rapidly in the initial stage and then gradually to reach palteau. Shaking agitates the reaction rate in the initial stage but does not affect after the system reached steady state. Ca and si concentrations show rapid increase and then gradual increase. Al concentration increases rapidly in the early stage and then decreases. Later decrease was interpreted as the precipitation of an Al-bearing material. Different dissolution rates of different constituents of plagioclase together the with precipitation of al-bearing material might be responsible for the non-stoichiometric dissolution of plagioclase.X-ray diffraction analyses on anorthosite before and after dissolution experiment show dissolution rates differ with different lattice planes of plagioclase. It suggests the crystallographic control on dissolution reaction. X-ray photoelectron spectroscopic result shows that the average composition of plagioclase surface reacted with HCL of initial pH 1.97 for 2000 hours is Na0.20Ca0.26Al1.7Si2.3O8. It means that Na- and Ca-depleted H-feldspar is developed without Al-depleted layer on the surface of plagioclase by reaction with HCl and that dissolution reaction takes place sparsely on the surface of plagioclase. Al and Si are dissolved preferentially over Ca from anorthosite powder in KHO solution. Reaction of acid-reacted anorthosite with KOH solution shows the same Si dissolution behavior as in the fresh anorthosite. This indicates that the Al-depleted and Si-enriched layer does not build up on the acid-reacted surface.