Gneiss Characteristics and Minerals
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What is the main characteristic of gneisses?

  • Gneisses have a smooth texture.
  • Gneisses have a glassy appearance.
  • Gneisses are characterized by gneissic layering. (correct)
  • Gneisses are soft and easily crumble.
  • Which type of minerals are responsible for the alternating light-colored bands in gneisses?

  • Garnet and sillimanite
  • Magnetite and hematite
  • Biotite and amphibole
  • Quartz and feldspar (correct)
  • What can rigid feldspar grains sheared into oval eye-shaped crystals produce in gneisses?

  • Augen gneiss (correct)
  • Sillimanite
  • Corundum
  • Cordierite
  • What is the term for lens-shaped grains that quartz grains in gneisses can be sheared into?

    <p>Flaser</p> Signup and view all the answers

    What are orthogneisses and paragneisses determined by?

    <p>Their protoliths</p> Signup and view all the answers

    Which type of protolith can result in gneisses referred to as granite gneiss?

    <p>Granites</p> Signup and view all the answers

    What is the main reason behind the development of gneissic foliations?

    <p>Layer transposition and segregation of minerals</p> Signup and view all the answers

    In gneissic banding, which type of minerals are typically concentrated in fold limbs?

    <p>Micas and inosilicate minerals</p> Signup and view all the answers

    What process results in the production of igneous layers enriched in quartz and feldspar between refractory layers enriched in dark-colored ferromagnesian minerals?

    <p>Partial melting (anatexis) and differentiation</p> Signup and view all the answers

    Which type of minerals have higher melting temperatures compared to quartzofeldspathic minerals according to the text?

    <p>Dark-colored ferromagnesian minerals</p> Signup and view all the answers

    What role does layer transposition play in the development of gneissic banding?

    <p>It pulls apart earlier folded layers leading to separate light and dark bands</p> Signup and view all the answers

    Which process is responsible for the development of gneissic foliations by creating alternating light and dark color bands?

    <p>Layer transposition</p> Signup and view all the answers

    What does a 'lit par lit intrusion' refer to?

    <p>Intrusion of granitic magma into mafic country rock</p> Signup and view all the answers

    What characteristic makes gneisses unsuitable for easy splitting?

    <p>Crude foliation</p> Signup and view all the answers

    At what temperature range do gneisses typically form in dynamothermal settings?

    <p>600°C and above</p> Signup and view all the answers

    Which type of rocks possess both igneous and metamorphic characteristics?

    <p>Migmatites</p> Signup and view all the answers

    What is a distinguishing feature of migmatites compared to gneisses?

    <p>Irregular, swirling mix of colors</p> Signup and view all the answers

    At what temperature can extensive melting of gneiss lead to the formation of migmatites?

    <p>~700°C</p> Signup and view all the answers

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