Trends of enrichment of free mica grains in crushed rock aggregates

The paper reports a study of the behaviour of free mica grains in crushed rock aggregates of metamorphic origin undertaken to identify any typical trends of enrichment with grain size. The mineralogical composition of the various grain size fractions was obtained using a polarizing microscope and point counting. Two general trends of enrichment of mica are presented: Type I (isotropic source rock) and Type A (anisotropic source rock). Type I is associated with a general increase in free mica towards the finer fraction, with or without a peak for “coarser” grain fractions. Type A is associated with an increase in free mica up to a certain grain fraction, after which there is a decrease with progressively smaller grain size.