Earth Systems 3209
Unit: 3
Earth’s Materials
Reference:
Chapters 2, 3, 6, 7; Appendix A & B
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Unit 3:
Topic 5.2
Metamorphic Textures
Focus on . . .
 identifying and describing how different metamorphic
textures form.
 identifying various metamorphic rocks that exemplify each
texture.
 describing the result metamorphism has on selected parent
rocks including; limestone, sandstone, shale and granite.
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Metamorphic Textures
 Metamorphism literally means to “change form.”
 The degree of metamorphism is reflected in the rocks
texture and mineralogy.
METAMORPHISM CHANGES TEXTURE
 Two textures are formed as a result of metamorphism;
1) Foliated Texture
2) Non-Foliated Texture
Text Reference:
Pages 193-197
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Metamorphic Textures Depends On;
1) Alignment of minerals
 Directional stress causes minerals to align when recrystallizing.
The orientation of these minerals is usually perpendicular to the
compressional forces (direction of stress).
 This gives the resulting metamorphic rock a layered appearance.
 This is common during high-grade metamorphism and often
produces a foliated texture. Example: Gneiss
Gneiss
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Metamorphic Textures Depends On;
2) Recrystallization of minerals
 Pressure causes minerals to recrystallize which
generally forms larger, more dense crystals.
 The recrystallization process causes some metamorphic
rocks to display visible crystals with no visible evidence
of the original mineral grains. For example, quartz
sandstone changes to form quartzite.
 This is common during low-grade metamorphism and
often produces a non-foliated texture.
Quartz
Sandstone
Recrystallizes
Quartzite
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Metamorphic Textures
Foliated
 Two types of textures:
1) Foliated (i.e. layered or banded)
2) Non-foliated.
 Note that the texture of a metamorphic
rock is usually coarser than the parent
rock (i.e. previous rock).
Non-foliated
 Note that volume is often reduced as
increased pressure is often the result
of metamorphism.
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Metamorphic Textures
 Two textures are formed as a result of metamorphism:
1) Foliated Texture
 Results when the minerals of a rock are brought
into parallel alignment during recrystallization.
 Produces a banded or layered appearance.
 Examples: Slate, Phyllite, Schist & Gniess
 Granite when metamorphosed forms Gneiss.
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Metamorphic Textures
 Two textures are formed as a result of metamorphism:
2) Non-Foliated Texture
 Results when the minerals of a rock are recrystallized
creating uniform sized crystals with no visible foliation.
 This occurs when limestone (consist of pure calcite)
undergoes metamorphism and the smaller calcite
crystals combine to form larger interlocking crystals.
This process of recrystallization of calcite forms Marble.
 Examples: Quartzite & Marble
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Marble
Metamorphism of Parent Rocks:
 Note that some parent rocks include
1) limestone, sandstone, and shale which are
all sedimentary rocks.
2) granite is an igneous rock.
 Examples of foliated and non-foliated
metamorphic rocks include:
1) Foliated – slate, phyllite, schist, and gneiss
2) Non-foliated – quartzite and marble.
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Metamorphism of Parent Rocks:
Parent Rock
Changes to
Metamorphic Rock
Limestone
(Sedimentary)
Changes to
Marble
Sandstone
(Sedimentary)
Changes to
Quartzite
Shale
(Sedimentary)
Changes to
Granite
(Igneous)
Changes to
Slate
(Phyllite – Schist - Gniess)
Gniess
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Example 1:
Which feature identifies the metamorphic rock below?
(A) bedding
(C) striation
(B) foliation
(D) varves
Which rock type forms from the recrystalization and
reorganizing of minerals?
(A) Igneous
(B) Metamorphic
(C) Sedimentary
(D) Volcanic
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Example 2:
Which is the correct sequence in the metamorphism
of shale?
(A) phyllite - gneiss - slate - schist
(B) phyllite - slate - gneiss - schist
(C) slate - phyllite - schist - gneiss
(D) slate - schist - phyllite - gneiss
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Your Turn . . .
Take the time and complete the following questions . . .
(Solutions to follow)
Question:
Using examples, distinguish between foliated
and non-foliated metamorphic rocks.
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Solutions . . .
Question:
Using examples, distinguish between foliated
and non-foliated metamorphic rocks.
Answer:
Foliated: show layering or banding of different minerals
created by the alignment of minerals during directional
stress and recrystallization (Ex: schist, gneiss).
Non foliated: a mass or network of interlocking crystals
consisting of one mineral with no visible layering or banding
(Ex: marble, quartzite).
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Summary . . .
Overview of Points covered:
 Two Metamorphic Textures:
1) Foliated
2) Non-Foliated
 Metamorphism Depends on:
1) Alignment of minerals
2) Recrystallization of minerals
 Parent – Metamorphic rock pairs:
Limestone – Marble
Sandstone – Quartzite
Shale – Slate (Phyllite – Schist – Gneiss)
Granite – Gneiss
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