Abstract: The Hırka diatomaceous earth deposit from Taşhan formation in the north of Kayseri (Central Anatolia)is Lower Pliocene age. Chemical analyses have been performed for quality tests and study of the origin. The results ofthe mathematical correlations show three element-assemblages in opal-, carbonate-, and detritic minerals (clay-minerals,plagioclases and others from volcanics) groups. Montmorillonite minerals are identified in diatomaceous earth layers.Based on paleogeography, distribution of the flora and clay minerals and on siliceous concretions, the origin of thedeposits is explained with silica - rich, postvolcanic springs and silicate alteration.