SAPONITE AND VERMICULITE IN AMYGDALES OF THE GRANBY BASALTIC TUFF, CONNECTICUT VALLEY
SAPONITE AND VERMICULITE IN AMYGDALES OF THE GRANBY BASALTIC TUFF, CONNECTICUT VALLEY
复制标题
DOI：
10.1346/ccmn.1992.0400104
复制
发表时间：
1992-02-01
影响因子：
2.2
通讯作者：
KELLER, DM
中科院分区：
文献类型：
--
作者：
APRIL, RH;KELLER, DM
对康涅狄格河谷下侏罗统花岗岩玄武岩凝灰岩中的杏仁岩进行了表观热液成因的粘土分析，发现其由两个结晶良好的富铁三八面体2：1层可膨胀的层状硅酸盐组成。通过化学分析和X射线衍射分析，初步确定矿物为皂石和蛭石。皂石主要以二水水化状态存在，但也表现为一水层和三水层水化状态，这表明层间电荷分布不均，这一现象在蒙脱石中并不少见。第二种粘土的身份仍然不明确，但X射线衍射分析，特别是关于粘土的膨胀特性的分析，表明它是一种蛭石。Granby粘土结晶良好的性质和大尺寸(高达1 mm)的粘土薄片使我们能够使用SEM/EDS X射线成像和斑点分析技术来尝试检测皂石和蛭石之间的化学差异。结果表明，杏仁核内部和杏仁核之间的单个晶体的化学成分基本一致。这表明皂石和蛭石在化学上是相似的，它们膨胀性能的变化是由其他因素引起的，如晶体大小、层电荷密度或单位层内的电荷局部化。用岩相学和扫描电子显微镜观察了花岗岩粘土中的晶体尺寸差异。层内电荷密度或单位层内电荷局部化的变化可能受到Fe2+氧化为Fe3+的影响，这种转变是从观察到的较大杏仁核从绿色到棕色的变化推断的。Granby粘土具有特别重要的意义，因为它是两种结晶良好、富铁的三八面体2：1层可膨胀层状硅酸盐自然混合的少数例子之一，具有晶体化学和膨胀特性，似乎架起了蒙皂石和蚯蚓石族的操作定义的桥梁。
Clay of apparent hydrothermal origin that fills amygdales in the Granby Basaltic Tuff (Lower Jurassic) of the Connecticut Valley was analyzed and found to consist of two exceptionally well-crystallized Fe-rich, trioctahedral 2:1 layer expandable phyllosilicates. Based on chemical and XRD analyses, the minerals were tentatively identified as saponite and vermiculite. The saponite exists predominately in the two-water hydration state, but also displays one- and three-water layer hydration states, which suggests heterogeneous layer charge distribution-a phenomenon not uncommon in smectites. The identity of the second clay remains equivocal, but XRD analyses, especially with regard to the swelling properties of the clay, indicate that it is a vermiculite. The well-crystallized nature of the Granby clay and the large size of the clay flakes (up to 1 mm) allowed us to use SEM/EDS X-ray imaging and spot analysis techniques in an attempt to detect chemical differences between the saponite and vermiculite. Results showed that the chemistry of individual crystals, within and among amygdales, was essentially uniform. This suggests that the saponite and vermiculite are chemically similar and that variations in their swelling properties result from other factors, such as crystal size, layer charge density, or charge localization within the unit layers. Crystal size differences in the Granby clay were observed with both the petrographic and scanning electron microscope. Changes in layer charge density or charge localization within unit layers could have been affected by the oxidation of Fe2+ to Fe3+, a transformation inferred from the green-to-brown color changes observed in the larger amygdales. The Granby clay is of special importance, because it is one of the few examples of a naturally occurring mixture of two well-crystallized, Fe-rich trioctahedral 2:1 layer expandable phyllosilicates with crystallochemical and swelling properties that appear to bridge the operational definitions for the smectite and vermiculite groups.