Interstratification in Vermiculite
Clays and clay minerals
VER~IICULITE (Libby, Mont.) was ground in a Waring blender in a 1 ~ NaCI solution and, after removal of excess electrolyte, the clay fraction was separated by sedimentation. The clay was predominantly vermiculite : X-ray diffraction patterns of Ca-saturated and oriented specimens showed an intense and sharp 15~ and a weak 25~ diffraction maxima and their integral orders. The intensity of the 25 A reflection, attributed to regularly interstratified layers of vermiculite (15 ~-) and mica (10 ~),
... ) and mica (10 ~), was less than 20 ~o of the 15/~ peak. Additions of varying amounts of potassium or cesium, ranging from 10~ to 100~o of exchange capacity, to Ca-saturated clay showed that the collapse of the vermiculite lattice proceeds through a 1:1 regular interstratification of a 15~ and a 10/~ lattice. Successive additions increased the 25/~ diffraction peak at the expense of the 15A reflection until the entire sample was interstratified. Further additions of K (or Cs) reduced the intensity of the 25/~ reflection and produced a 10 it reflection until the entire sample was collapsed to 10/~ and no 25/~ reflection was recorded. These observations point out that under certain environmental conditions, the diagenetie formation of micas from vermiculite may proceed through an interstratification of the two in a manner analogous to weathering of biotite to vermiculite through an interstratified stage. One-dimensional Fourier synthesis from the intensities of the 001 diffraction maxima of the interstratified mixture was carried out. In addition, a mechanism for the formation of the interstratified mixture was postulated: the rep]acement of Ca by i (or Cs) in one layer reduces the effective negative charge on the adjacent layer. Consequently, the K cannot replace the Ca in this but replaces the Ca in the next layer forming the interstratified mixture.