1. 8. METAMORPHIC ROCKS

2. METAMORPHISM
SHALE
Metamorphism is the solid-state change in rocks produced by increased heat (T) & Pressure (P).
GNEISS
P (K bar)
The formation of metamorphic minerals and textures takes place very slowly (thousands to millions of years). 1-
15-
25-

3. Clay minerals (made of elements such as Al, Si, O, K, Mg, etc.)
Gneiss
Shale
Changes involve: Rock composition; texture/structure
SHALE
GNEISS
Composition
Clay minerals (made of elements such as Al, Si, O, K, Mg, etc.)
Garnet, Plagioclase, Amphibole, Pyroxene
Texture & Structure
Soft, light in weight, made of very small to microscopic minerals
Hard, dense, coarse-grained, sometimes folded

4. METAMORPHIC REACTION (NEOCRYSTALLIZATION)
involves chemical reactions that decompose older minerals and produce new minerals.
Example: SiO2 + CaCO3  CaSiO CO2
Quartz Calcite Wollastonite
Wollastonite (metamorphic mineral)
Impure Limestone

5. Example 1: Limestone  Marble
RECRYSTALLIZATION: changes the shape and size of minerals without changing the chemical composition of the minerals.
Example 1: Limestone  Marble
CaCO3
CaCO3
Example 2: Sandstone  Quartzite
SiO2
SiO2
SiO2
Quartz Sandstone
Quartzite

6. METAMORPHIC GRADE
Refers to the intensity of heat to which a rock was subjected.
Low Grade
Temp: C
Depth: < 6 miles
P: 3-4 Kbars
Medium Grade
Temp: C
Depth: 6-25 miles
P: 4-12 Kbars
High Grade
Temp: C
Depth: miles
P: Kbars L M H

7. RISING MAGMA AS A SOURCE HEAT
When magma gets in contact with rocks it causes the temperature of the rock to rise and result in metamorphism.

8. C C C C

9. METAMORPHIC TEXTURES 1. Foliated Metamorphic Rocks SLATE
Refers to whether metamorphic rocks possess a layered appearance or not.
1. Foliated Metamorphic Rocks
Presence of minerals such as mica and chlorite give the rock a layered appearance
SLATE
2. Non-foliated Metamorphic Rocks
Lack layered appearance, thus are massive
Amphibolite

10. 1. Foliated Metamorphic Rocks
A. SLATE
Clay minerals in original rock (shale) break down & form very fine grained (microscopic) crystals of biotite, muscovite & chlorite.
Shale is a very common sedimentary rock. Consequently metamorphic rocks derived from shale are also very common. As shale is subjected to higher and higher grades of metamorphism, different metamorphic rocks form.
Protolith: Original, pre-metamorphosed rock
V) Low-grade metamorphic rock
Clay minerals in original rock (shale) break down & reform into very fine grained (microscopic) crystals of biotite, muscovite & chlorite.
The microscopic minerals give the rock a dull surface & also define a thin foliation along which the rock breaks readily  Slaty cleavage
shale
SLATE

11. slate walkway
Slate roof
Slate roof
Slate chalkboard

12. B. PHYLLITE
Made up of very small crystals of muscovite & chlorite that give the rock a sheen.
Commonly shows a wavy, wrinkled surface

13. C. Schist
Made up of crystals of mica (muscovite & biotite) that are larger than in slate & phyllite and are easily visible  Glittery appearance.

14. D. Gneiss
Temperatures are above the stability range of most micas, so the micas in schist break down to form large crystals of feldspars & other minerals
It is a layered rock, with alternating light-colored minerals and dark-colored minerals

15. 2. Non-foliated Metamorphic Rocks
QUARTZITE
MARBLE
Hardness test: Qtz in Qzt has H7; calcite in LST has H3; scratch them with a H5 mineral, the one that scratches is calcite  marble!
Apply few drops of HCl, the one that effervesces is calcite  Marble
Parent rock?
Sandstone
Parent rock?
Limestone

16. Some Uses of Metamorphic Rocks
Washington Monument

17. Marble, because of its workability, is a widely used building stone.
Lincoln Memorial in Washington, D.C.
Taj Mahal, India
Marble, because of its workability, is a widely used building stone.

18. Increased heat & pressure
COAL
Peat
Unconsolidated
plant remains
Lignite
Increased heat & pressure
Bituminous coal
Anthracite coal
T > 2000C (Metamorphic )
Peat
Lignite
Bituminous coal
Anthracite coal

19. TEST YOUR KNOWLEDGE For the metamorphic rock shown
answer the following questions:
Is the rock foliated or non-foliated?
If foliated, determine whether it is slate, phyllite, schist or gneiss
At what temperature range could the rock have formed?
If the temperature on the rock in the picture was increased by 3000C, the rock that would form would be (choose one):
a) Sedimentary b) Igneous c) Metamorphic
5) What was the parent rock for the rock in this picture?