"' Palygorskite "'or "'attapulgite "'is a magnesium aluminium H 2 O ) that occurs in a type of clay soil common to the Southeastern United States.
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The chemical composition of the compound was determined by powder diffraction in the 1950s and was found to be a composite of palygorskite and indigo, most likely derived from the leaves of the " a�il ".
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The blue coloration seen on Maya and Aztec codices, and early colonial-era manuscripts and maps, is largely produced by the organic-inorganic mixture of " a�il " leaves and palygorskite, with smaller amounts of other mineral additives.
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A reminder of the extraordinary span of Beer's geological career is the story of the specimen from a Devonshire cave that he sent to London for identification, and which evoked a response more than 70 years later that he had indeed identified it correctly as palygorskite.
