Section Assessment, p'113

1
Section Assessment, p.113

• 1) 3 Major types of Igneous rocks What are
  ultramafic rocks?
• a- Felsic (light color, high Si, contain quartz
  and feldspars) Intermediate (medium color, lower
  Si, contain moderate biotite, amphibole,
  pyroxene) Mafic (dark color, low Si, rich Fe-Mag
  minerals biotite, pyroxene, amphibole, olivine)
• b- Ultramafic Low Si, very high Fe Mg, dark
  green.
• 2) Why does rhyolite have smaller crystals than
  granite ?
• Rhyolite cooled faster. The crystals did not
  have time to grow large.
• 3) What chemical property is most commonly used
  to classify igneus rocks? List 2 physical
  properties useful for igneus rocks id.
• a- Chemical composition ( silica)
• b- Color, grain size, texture.
• 4) Why is Au often found in quartz veins
  in/around igneous intrusions?
• Au is not incorporated into the common igneous
  materials. It remains in solution longer that
  most other materials (together with silica and
  water) and it becomes concentrated. Then, quartz
  veins (with Au) may form in/around igneous
  intrusions.
• 5) Would quartz or plagioclase be more likely to
  form well-shaped crystals ?
• Plagioclase is more likely to form well-shaped
  crystals. It forms early and there is room in the
  liquid magma for crystals to grow. Quartz
  crystallizes among the last and fills-in the
  spaces between previosuly formed mineral grains.
• 6) Concept making
• Types of igneous rocks
• Felsic granite Intermediate Diorite
• Mafic gabbro Ultramafic - peridotite