(7) Metamorphic Rocks

Question 1

Metamorphic Rocks

Answer 1

‘Changed’ rock: earth’s interior

Question 2

Under what conditions does the rock metamorphose?

Answer 2

• Deep burial (high P and T)
• Tectonic forces (high P some T)
• High temperatures

Question 3

What changes occur in the rock during metamorphism?

Answer 3

• Recrystallization: coarser grained
• Reactions to form new minerals: reflect equilibrium
• These changes take place in a solid state (melting isn’t needed)

Question 4

Metamorphic changes are influenced by…

Answer 4

• Chemical compositions of rock
• Temperature
• Pressure
  o Confining pressure (applied equally in all directions)
  o Differential stress (forced are stronger or weaker in different directions)
  o Compressive* (squeezing)
  o Tensional (stretching)
  o Shearing
• Water (agent to transport ions between grains)
• Time (important)

Question 5

Classifying metamorphic rocks

Answer 5

• Primarily based on texture
• Foliated: rock has a planar texture
• Nonfoliated: minerals have a random texture

Question 6

Foliated Rocks

Answer 6

• Slate (like mudstone or shale) (least affected by metamorphism)
  • Rocks splits into thin, flat sheets
  • Clay and other sheet silicates
  • Very fine grained
• Schist (regrowth of flakey minerals)
  • Minerals have planar alignment (visible and platy or elongated minerals)
  • Add mineral names to describe the composition (ex: biotite-garnet schist)
• Gneiss (highest grade, most P and T)
  • Light and dark minerals occur in separate, parallel layers/lenses (no one knows why)
  • Add mineral names to describe the composition (ex: quartz-feldspar-hornblende gneiss)

Question 7

Nonfoliated Rocks

Answer 7

• Name based on MINERAL CONTENT
• Parent Rock (Metamorphic Rock)
• Lime stone (Marble)
• Quartz Sandstone (Quartzite)
• Shale (Hornfels)
• Basalt (Hornfels)