The Middle-Upper Miocene-Pliocene sediments near Polatli contain commercial sepiolitic clay deposits. The sepiolite-rich Polatli basin sediments were studied to describe the sepiolitic clay deposits of the area and to assess the environments of formation using X-ray diffraction, optical and scanning electron microscopy, and chemical analysis. The Polatli basin is an elongated, rift-related graben trending NE-SW in central Turkey, filled with continental Late Miocene to Early Pliocene sediments. The sediments which comprise claystone, marl and limestone, dolostone, and evaporites are characteristic deposits of low-salinity, playa-lake depositional environments. These sepiolite-rich deposits include sepiolite, dolomite, and calcite, with minor amounts of palygorskite, quartz, moganite, amorphous silica (opal-CT), and feldspar.