Retrieving "Geological Impurity" from the archives

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1. Quartzite

   Linked via "impurities"

   Composition and Impurities
   Pure quartzite is nearly $100\%$ quartz (mineral)/), making it inherently white or colorless. However, in nature, impurities inherited from the source sandstone are common and dictate the final coloration and auxiliary physical properties.
   Coloration Mechanisms