Spectroscopic and TEM studies of phyllosilicates in carbonaceous chondrite

Cm球粒陨石经历了水蚀变。由于水蚀变，球粒体内的中晶相被层状硅酸盐取代。这种叶状硅酸盐的颜色多种多样，如绿色、黄绿色、黄棕色、红棕色等。本研究采用可见光光谱分析和电子探针分析等方法，对墨其逊、墨里、Y75293、Y791198、Mighei、Nogoya和Y82042中的叶滑石进行了研究。用L*a*b*比色系统对这些层状硅酸盐的颜色进行了定量比较。与不同蚀变程度的CM球粒陨石中的层状硅酸盐的成分变化相比，层状硅酸盐的颜色变化是复杂的。颜色变化的复杂性取决于在层状硅酸盐形成过程中遭受蚀变的矿物和氧化还原状态的差异。层状硅酸盐的颜色差异是由于700 nm左右的宽吸收带(可能是由于Fe^&lt；3+&gt；与Fe^&lt；2+&gt；之间的IVCT)和450-500 nm左右的肩部(可能是由于六个配位的Fe^&lt；3+&gt；阳离子)所致。预计绿色层状硅酸盐和红棕色层状硅酸盐具有不同的Fe^&lt；3+&gt；/Fe^&lt；2+&gt；比值。我们正在寻找一种简便的方法来获得蛇纹石族矿物中的Fe^&lt；3+&gt；/Fe^&lt；2+&gt；；

CM chondrites experienced aqueous alteration. Due to the aqueous alteration, mesostses in chondrules were replaced by phyllosilicates. Such phyllosilicates are various in colors, for example, green, yellowish green, yellowish brown, reddish brown, and so on. In this study, phylloslicates in Murchison, Murray, Y75293, Y791 198, Mighei, Nogoya, and Y82042 were investigated by visible light spectroscopy and electron microprobe analysis. Colors of such phyllosilicates were compared quantitatively by using L*a*b* color system. Compared with compositional variation of the phyllosilicates among differently altered CM chondrites, changes in colors in the phyllosilicates are complex. Complexity of changes in color depends on both the differences in minerals which suffered alteration and redox states during phyllosilicate formation. Differences in colors in phyllosilicates are due to broad absorption band around 700 nm (probably due to IVCT between Fe^<3+> and Fe^<2+>) and a shoulder around 450-500 nm (probably due to six coordinated Fe^<3+> cations). It is expected that green phyllosilicates and reddish brown ones have different Fe^<3+>/Fe^<2+> ratios. We are now seeking a convenient method to acquire Fe^<3+>/Fe^<2+> ratios in serpentine-group minerals.