Lecture 9// Metamorphic Rock

Question 1

Metamorphism (5)

Answer 1

Changes to the mineralogy and texture of pre-existing rock due to:

• increased pressure
• increased temperature
• increased chemically active fluids

Solid-state transformations (no or very little melting involved).

Question 2

Parent rock / Protolith (2)

Answer 2

The original (pre-existing) rock type before it underwent metamorphism.
-ex. Shale (or mudstone) is a common parent rock of slate.

Question 3

Foliation (2)

Answer 3

Some metamorphic rocks show a preferred orientation to the grains (layering or alignment) as a response to a directed stress.
-ex. Granite to Gneiss

Question 4

Regional Metamorphism (1)

Answer 4

Directed stress occurs due to compressive forces acting within large regions at and adjacent to convergent plate margins.

Question 5

Metamorphic Grade (5)

Answer 5

The grade reflects the severity of the metamorphic conditions, increasing grain size & metamorphic grade:

• Lowest: Slate
• Phyllite
• Schist
• Highest: Gneiss

Question 6

Slate (3)

Answer 6

• very fine grained & dull
• slaty cleavage (breaks into very flat layers)
• clay minerals, chlorite muscovite

Question 7

Phyllite (3)

Answer 7

• fine-grained
• phyllitic texture (glossy metallic shine, commonly wavy)
• chloride, muscovite

Question 8

Schist (3)

Answer 8

• medium to coarse grained
• commonly some grains are much larger (porphyroblasts)
• schistose texture (scaly)
• muscovite, biotite, kyanite and others

Question 9

Gneiss (3)

Answer 9

• medium to coarse grained
• gneissic texture (bands of light and dark minerals)
• feldspar, quartz, muscovite, biotite. Fe and Mg

Question 10

Contact Metamorphism (1)

Answer 10

Nonfoliated metamorphic rocks are common where there is only lithostatic stress in addition to heat from magma intrusions.

Question 11

Quartzite (3)

Answer 11

• medium to coarse grained
• visually can look like marble, but is much harder (scratches glass)
• sandstone parent rock

Question 12

Marble (4)

Answer 12

• medium to coarse grained
• soft
• reacts easily with acid if it is calcite, slow reaction if dolomite
• limestone or dolostone parent rock

Question 13

Hornfels (2)

Answer 13

• fine grained, dark

- shale/mudstone parent rock

Question 14

Soapstone (4)

Answer 14

• fine or medium grained
• soft, soapy feel
• Peridotite parent rock
• composed primarily of talc, with varying amounts of chlorite, mica amphiboles, carbonates, and other minerals