Mixed-layer kerolite/stevensite from the Amargosa Desert, Nevada

Mixed-layer clays composed of randomly interstratified kerolite/stevensite occur as lake and/or spring deposits of probable Pliocene and Pleistocene age in the Amargosa Desert of southern Nevada, U.S.A. The percentage of expandable layers of these clays, determined from computer-simulated X-ray diffractograms, ranges from almost 0 to about 80%. This range in expandabilities most likely results from differences in solution chemistry and/or temperature at the time of formation. An average structural formula for the purest clay (sample P-7), a clay with about 70% expandable layers, is:

[(Mg_2.72Al_0.07Fe_0.03Li_0.09)(Si_3.96Al_0.04)O₁₀(OH)_0.2]^-0.21[X⁺_0.21]^+0.21

The data suggest that talc, kerolite, and stevensite form a continuous structural series based on layer charge.