충남지역 사문암은 주로 사문석으로 구성되어 있으며, 감람석 기원의 사문석은 감람석의 가상을 이루고 있고 이 사문석결정들의 외곽을 자철석들이 둘러싸서 전체적으로 망상구조를 보인다. 또한 사문암중에는 부분적으로 기원암인 더나이트와 해즈버자이트의 잔류 구성광물인 감람석과 휘석이 이들의 결정경계나 결정내 간극을 따라 사문석화가 일어났다. 감람석에서 사문석으로 변할 때 Mg 이온은 크게 감소하고, Si 이온은 크게 증가하였으며 Fe2+ Fe3+ 이온이 약간 감소하였고, 이 철들이 자철석을 형성하였다. 휘석에서 사문석으로 변할 때 Si 이온은 크게 감소하고 Mg 이온은 크게 증가하였으며, 기타 이온은 별 변화가 없다. 충남지역 사문암의 기원암인 더나이트와 해즈버자이트로부터의 사문석화작용은 기원암이 형성된 후 작용한 여러 가지 물에 의해서, 그리고, 녹색편암상 내지 각섬암상에서 백립암상에 이르는 변성작용시의 변성수의 영향으로 이루어졌다.

Serpentinite of the Yesan-Gongju-Cheongyang area has been formed by serpentinization of ultramafic rocks. The ultramafic rock might be composed mainly of oilvine with minor pyroxene and amphibole. Olivine has a considerably restricted chemical compositional ranging from Fo90 to Fo93. Fresh serpentinite containing large amount of oilvine is usually massive in occurrence and dark green to black in color. Serpentine minerals occur not only as major mineral of serpentinite, but also as remnants in the talc ore which was formed from serpentinite. XRD study indicates that antigorie is the most abundant serpentine mineral of the serpentinite. Serpentinite consisting of antigorite usually shows non-pseudomorphic texture, whereas that consisting of lizardite shows pseudomorphic texture. Antigorite is found along the margins or fractures of olivine grains resulting in the formation of network of magnetite which was formed at the time of serpentinization. Lizardite, subordinate constituent mineral of serpentinite, frequently shows pseudomorphic mesh-texture after olivine. The chemical differences between antigorite and lizardite/chrysotile are small, so both minerals are not easily discernible with the electron microprobe. Antigorite occuers as elongate blades, flakes, or plates forming interpenetrating texture to obliterate previous textures. SEM study also shows that most serpentine minerals occur in platy or tabular form rather than in asbestiform. Fractures formed after main serpentinization are observed within the pseudomorphic central olivine grain. Careful observation of the serpentine pseudomorphs gives a great deal of data on the pre-serpentinization nature of the serpentine pseudomorphs gives a great deal of data on the pre-serpentinization nature of the ultramafic rocks. It is inferred that the serpentinization took place after the emplacement of ultramafic body into the relatively wet environment ceased and the cooling intrusive body crossed into the stability field of serpentine. It is inferred that the final pervasive serpentinization took place over a long time, by hydrothermal water supplied through the fracture system produced during emplacement of ultramafic rock.