南部丹沢山地の中新世丹沢層群に産出する粘土鉱物の構造的性質と化学組成は変成度に伴って規則的な変化傾向を示す。スメクタイトは束沸石と濁沸石帯に，C/S不規則混合層鉱物は束沸石，濁沸石とブドウ石—パンペリー石帯に，C/S規則混合層鉱物は束沸石帯に分布する。C/S不規則混合層鉱物中のスメクタイトの割合は変成度の高まりに伴って，70-100%，40-50%，20-30%と0-10%という段階的に変化する。緑泥石は最初に濁沸石帯に産出し，ブドウ石—パンペリー石帯に卓越し，緑れん石と緑れん石—アクチノ閃石帯に唯一の粘土鉱物になる。緑泥石のFe/（Fe+Mg）は全岩組成に支配される。 Si含有量は変成度が高くなるにつれて低くなる。

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Two stages of metamorphism, initial and main stages, are distinguished on the basis of textural features and chemical compositions of sodic amphiboles and associated minerals in the Kamuikotan high-pressure and low-temperature metabasites. The initial stage is detected by sodic amphiboles rimmed by actinolite and enclosed by epidote porphyroblast in the metabasites. These sodic amphiboles are optically and chemically heterogeneous, and range in chemical composition from crossite to glaucophane (Al₂O₃ content: 2.6-10.5 wt.%). The main stage is characterized by the occurrence of epidote, pumpellyite, chlorite, calcite, hematite and jadeite component poor sodic pyroxene in the metabasites. Amphiboles coexisting with these minerals are actinolite, winchite and magnesioriebeckite (Al₂O₃ content: 0-2.9 wt.%).
     These variations of modes of occurrence and chemical compositions of sodic amphiboles suggest that some studied metabasites initially had been metamorphosed under low grade condition with a relatively high ratio of pressure/temperature and were subsequently converted to assemblages of the main stage, correspond to the pumpellyite-actinolite facies, by decline in the pressure/temperature ratio with local effect of deformation and metamorphic fluid.

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