palygorskite, a fibrous magnesium aluminum silicate. The structure of palygorskite contains extended silicon-oxygen sheets, justifying the retention of the mineral in the layer silicate family, but the tetrahedral SiO4 groups forming these sheets are oriented in such a manner as to develop extended lathlike features that give rise to the fibrous morphology. The mineral occurs in sediments from playa lakes and saline deposits, in desert soils, and in calcareous material. Attapulgite is a variety of palygorskite found in Attapulgus, Ga. For chemical formula and physical properties of attapulgite, see clay minerals (table).