page_title: Piégut-Pluviers Granodiorite
section_title: Coarse-grained facies
hierarchical_section_title: Piégut-Pluviers Granodiorite / Petrological facies / Coarse-grained facies
caption_attribution_description: English: Common facies of the Piégut-Pluviers granodiorite, northwestern Massif Central, France.
context_page_description: The Piégut-Pluviers Granodiorite is situated at the northwestern edge of the Variscan Massif Central in France. Its cooling age has been determined as 325 ± 14 million years BP.
context_section_description: The coarse-grained or common facies takes up the largest surface area. Grain sizes vary in general between 2 and 6 millimeter with roughly isometric grains. The fresh rock has a grey colour; weathered outcrops can take on a brownish-reddish stain. It comprises the following minerals:
  quartz - rounded, globular grains of 1 to 3 millimeter in diameter, can form agglomerations with 1 to 3 centimeters in diameter − 26 volume percent
  plagioclase − often displays normal zoning, with calcic cores An ₃₃₋₃₅ (andesine) and more sodic rims An₂₅ oligoclase); some euhedral grains reach 10 millimeters and more − 42 volume percent
  orthoclase − perthitic, Carlsbad twinning, corroded by quartz, some euhedral crystals can reach more than 10 millimeters in grain size − 18 volume percent
  biotite − millimeter grain size, brass coloured, with zircon inclusions and often chloritized − 10 volume percent
  Accessories are zoned allanite, apatite, epidote, occasionally green hornblende, zircon and zoisite. An opaque mineral is pyrite.
  The coarse-grained facies sometimes contains dark, fine-grained rounded to subrounded inclusions that cover the centimeter to decimeter size range. The long axes of the feldspar grains show a preferred orientation in some places.
  This facies is normative in quartz (oversaturated in SiO₂) and in corundum (peraluminous). It is also subalkaline. In the alphabet-soup classification it represents an I-type granitoid of calcalkaline characteristics belonging to the K-series. Compared with average granodiorites, this rock type has a higher SiO₂ value and approaches the composition of monzonitic granites.
caption: Common coarse-grained facies of the Piégut-Pluviers Granodiorite
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