metamorphic rocks

Question 1

definition

Answer 1

formed deep within the earth by transformation of pre-existing rocks by heat, pressure, or both

• change textures/new minerals due to deformation/reorientation of mineral components, recrystallization of minerals into large grains, and chemical recombination
• come from both igneous and sedimentary

Question 2

Slate

Answer 2

• fine grained, foliated, homogeneous
• formed from fine-grained mudstone
• highly developed cleavage planes
• metamorphic grade= low from regional metamorphism

Question 3

phyllite

Answer 3

• from continued action of stresses upon slate
• minerals=quartz mica and chlorite
• metamorphism degree is between slate and mica schist
• larger minerals than slate
• metamorphic grade= low from regional metamorphism

Question 4

regional metamorphism

Answer 4

A type of metamorphism in which the mineralogy and texture of rocks are changed over a wide area by deep burial and heating associated with the large-scale forces of plate tectonics

Question 5

Schist

Answer 5

• originally clay and mudstone
• minerals are micas, chlorite, and hornblende
• flaky
• metamorphic grade=medium and also from regional metamorphism

Question 6

hornfels

Answer 6

• from thermal metamorphism of sedimentary rocks
• contains feldspar, biotite, and quartz
• metamorphic grade= high due to thermal metamorphism

Question 7

Quartzites

Answer 7

• originally sandstone changed by heat/pressure
• hard, resistant to chem weathering, and often forms ridges and hilltops
• doesn’t accomodate vegitation

Question 8

Gneiss

Answer 8

• from regional metamorphism of igneous or sed rocks
• medium to coarse foliated and largely recrystallized minerals
• minerals: feldspar, quartz, micas, or hornblende, and garnet
• metamorphic grade=high

Question 9

Marble

Answer 9

-from recrystallization of limestone in regional metamorphism or contact environments
-mostly calcite
-marble is also used to indicate stones that can reach levels of high polish
metamorphic grade=varies

Question 10

foliations

Answer 10

• indicates the mineral showing compositional banding
• basically realignment of particles due to stress creating planar fabric
• fabric forms at right angles to stress

Question 11

recrystallization

Answer 11

• hardening of material

- strengthens final rock structure

Question 12

Causes of metamorphism

Answer 12

• pressure from sinking deeper, continental collisions,

- temp from sinking into warmer layers, igneous hot lava (contact/thermal metamorphism), steam from hot vents

Question 13

anisotropic

Answer 13

having a physical property that has a different value when measured in different directions

Question 14

typical meta rocks in HK

Answer 14

• foliated: phylite and schist

- non-foliated: marble, hornfels, and skarn

Question 15

marble in HK

Answer 15

• from carboniferous period
• info is found from drillhole cores
• Yuen Long Formation: 600 mthick, UCS=50 MPa-140 MPa, silicified by contact metamorphism from granite intrusion
• Ma On Shan Formation: relatively pure marble, strongly foliated, min thickness of 200 m
• Tolo Harbour formation: carbonate rocks, occur as isolated blocks, up to 350 m thick, dark grey/pale grey/bluish grey/cream colored marble

Question 16

Engineering consideration

Answer 16

• affects engineering consideration by changing constituent minerals or by foliation
• foliation results in large anisotropic strength differences, usually lowers shear strength
• marble can have chemically worn cavities like limestone

Question 17

rock strength and resistance to weathering

Answer 17

type     grade     strength rtoweather
slate/     low         small            weak
phylite
schist/
marble
hornfels/
quartzites/
gneiss/
Marble   high         large             high