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Earth Systems 3209

Earth Systems 3209. Reference: Chapters 2, 3, 6, 7; Appendix A & B. Unit: 3 Earth’s Materials. Unit 3: Topic 5.2. Metamorphic Textures. Focus on . . . identifying and describing how different metamorphic textures form.

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Earth Systems 3209

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  1. Earth Systems 3209 Reference: Chapters 2, 3, 6, 7; Appendix A & B Unit: 3Earth’s Materials

  2. 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.

  3. 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; • Foliated Texture • Non-Foliated Texture Text Reference: Pages 193-197

  4. Metamorphic Textures Depends On; • Alignment of minerals • Directional stress causes minerals to align when recrystallizing. The orientation of these minerals is usually perpendicular to the compressionalforces (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

  5. Metamorphic Textures Depends On; • 2) Recrystallization of minerals • Pressure causes minerals to recrystallizewhich 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 Quartzite Recrystallizes

  6. Metamorphic Textures Foliated • Two types of textures: • Foliated (i.e. layered or banded) • Non-foliated. • Note that the texture of a metamorphic rock is usually coarser than the parent rock (i.e. previous rock). • Note that volume is often reduced as increased pressure is often the result of metamorphism. Non-foliated

  7. Metamorphic Textures • Two textures are formed as a result of metamorphism: • 1) Foliated Texture • Results when the minerals of a rock are broughtinto parallel alignment during recrystallization. • Produces a banded or layered appearance. • Examples: Slate, Phyllite, Schist & Gniess • Granite when metamorphosed forms Gneiss.

  8. 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 Marble

  9. Metamorphism of Parent Rocks: • Note that some parent rocks include • limestone, sandstone, and shale which are all sedimentary rocks. • granite is an igneous rock. • Examples of foliated and non-foliated metamorphic rocks include: • Foliated – slate, phyllite, schist, and gneiss • Non-foliated – quartzite and marble.

  10. Metamorphism of Parent Rocks: Changes to Changes to Changes to Changes to Changes to

  11. Example 1: Which feature identifies the metamorphic rock below? (A) bedding (B) foliation (C) striation (D) varves Which rock type forms from the recrystalization and reorganizing of minerals? Igneous (B) Metamorphic (C) Sedimentary (D) Volcanic

  12. 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

  13. Your Turn . . . Take the time and complete the following questions . . .(Solutions to follow) Question: Using examples, distinguish between foliated and non-foliated metamorphic rocks.

  14. 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 mineralwith no visible layering or banding (Ex: marble, quartzite).

  15. Summary . . . Overview of Points covered: • Two Metamorphic Textures: • Foliated • Non-Foliated • Metamorphism Depends on: • Alignment of minerals • Recrystallization of minerals • Parent – Metamorphic rock pairs:Limestone – Marble Sandstone – Quartzite Shale – Slate (Phyllite – Schist – Gneiss)Granite – Gneiss

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