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: $${[ {( {M{g2,72}A{l0,07}F{e0.03}L{i0.09}} )( {S{i3.96}A{l0.04}} ){O₁₀}{{( {OH} )}_2}} ]- 0.21}{[ {X0.21^ + } ]+ 0.21}.$$ The data suggest that talc, kerolite, and stevensite form a continuous structural series based on layer charge.