1. Chapter 10:
8th Grade Earth Science

2. Petrology: study of rocks & their classification/history
10A: Classifying Rocks
Petrology: study of rocks & their classification/history
In crust l
Geologist = scientist who specialize in thing related to the earth Petrologist= speacilization

3. 10A: Classifying Rocks To classify a rock ask:
How did it get here?
How has it changed?
Igneous: Rocks formed from lava
Sedimentary: Rocks formed from the compaction of sediment
Metamorphic: rocks that form from changes to existing igneous, sedimentary, or other metamorphic rocks
Igneous: #8-14, Sedimentary: #23-29, Metamorphic: #15-22

4. We classify rocks by… 10A: Classifying Rocks
Types of minerals it contains
Texture: its size, shape, look, & feel
Grains : small, hard piece or particle
By mineral type – some minerals are dark… Ex: Ignious basalt is dark (#11)
By texture – size and arrangement of mineral crystals… Ex: Granite (#13)

5. Large: coarse-grained texture
10A: Classifying Rocks
Types of grains:
Large: coarse-grained texture
Sharp and angular vs. smooth and rounded
Randomly arranged vs. organized bands
Microscopic: fine-grained texture
None: glassy look/transparent
Size, shape, and patterns of grains provide clues to how rock formed -> key to classifying them
U = coarse random L = coarse w/ organized bands Sedimentary: often tiny, sand-like mineral grains (23-29)
Contest: Best coarse grained-texture/ Banded / fine-grained texture / no grains

6. Basement Rock: deep rock above the mantle.
10B: Igneous Rocks
Basement Rock: deep rock above the mantle.
Basement rock (not bedrock): Always granites, basalts, or metamorphic rocks of these types that extend all the way to the mantle

7. ALL igneous rocks contain silicate minerals.
10B: Igneous Rocks
ALL igneous rocks contain silicate minerals.
Intrusive rocks: larger crystals = cooled slowly
Extrusive rocks: smaller crystals = cooled quickly
Not all rocks follow this model, therefore we have to look at original magma and surrounding conditions.
Magma composition, temperature, high pressure, the existence of seed crystals, rate of crystal formation affect grain size
Contest: igneous rock that probably cooled slowly / igneous rock that probably cooled quickly

8. 10B: Igneous Rocks
Course-Grained Igneous Rocks: large mineral grains [basaltic, andesitic, rhyolitic]
Classifications:
Pegmatite: large interlocking crystals
Porphyry: a few large mineral grains appear set in a very fine textured rock
Phanerite: a mass of distinct mineral grains that are small and similar in size
Mostly Intrusive
PEG muh tight (#13) POHR fuh ree (#12) FAN er ite (#8)
Ignious is #8-14

9. Mostly extrusive 10B: Igneous Rocks
Fine-Grained Igneous Rocks: small mineral grains [basalt, andesite, rhyolite]
Form at atmospheric pressure
Turbulent lava flows or
Ejected materials
Classifications:
Aphanitic: can’t see crystals w/ naked eye
Porphyritic: widely separated, large individual crystals immersed in a fine-grained rock
Mostly extrusive
Pg. 220 [chart of common igneous rocks]
aphanite (#11, 14)
Porphyritic (#12)

11. Volcanic lava: 10B: Igneous Rocks
Scoria: basaltic lava, sharp edged, spongy rock
Pumice: felsic lava that foams as it hardens; sponge- like
Obsidian: felsic lava that does not foam
Pantheon Pan-thee-on is made of Pumice show scoria and obsidian from kit

12. 10B: Igneous Rocks
Uses:
Buildings & gravestones: for strength and resistance to weather
Monuments & Statues: beauty, easily carved
Tower bridge: made of granite 1984

13. 10C: Sedimentary Rocks
Sedimentary: rocks created by the compaction of eroded sediments. (In 10A notes)
Stages of sedimentation:
Erosion and solution
Transportation & deposition
Compaction
Cementation

14. 10C: Sedimentary Rocks
Erosion: rocks broken apart by wind or water
Solution: water dissolving minerals and transporting them to other places

15. 10C: Sedimentary Rocks
Transportation: Solid particles carried usually by wind or water
Deposition: Solid particles dropped after being transported by wind or water.
Water speed will determine type of deposition.

16. 10C: Sedimentary Rocks
Compaction: deposits pressed more closely together due to the pressure of sediments settled on layers above.
Cementation: dissolved minerals fill gaps between sediments and glue particles together

17. Read 10.8 to yourself Clastic Non-Clastic Both
Clastic – made of eroded fragments, include conglomerates, breccia, siltstone, shale, may contain fossils
Both - Sedimentary
Non-Clastic – aka chemical, form from sediments that weren’t clasts, formed by chem precipitation or sediments from living things, can be organic or non-organic, can be coquina (shell rich limestone)

18. Clastic Sedimentary rock: made of eroded fragments. Types:
10C: Sedimentary Rocks
Clastic Sedimentary rock: made of eroded fragments.
Types:
Conglomerate: Coarsest, largest clasts (>2mm).
Spaces cemented by silica or calcite
Breccia: similar to cong., but clasts are sharp & angular
Sandstone: clasts between mm
Siltstones/shales: clasts <0.0625mm
Often contain fossils
High clay content = gray
Breccia: carried by fast flowing water U= cong L= shale

19. 10C: Sedimentary Rocks
Nonclastic (chemical) sedimentary rocks: formed from sediments that weren’t clasts of rock.
Types:
Inorganic
Precipitation: when a saturated solution cools or evaporates forming sediments
Ex: limestone (calcite), halite (natural table salt)
Organic
Sediments built up from actions of living things.
Ex. Rocks made of shells/skeletons, chalk
Clast = rock fragment

20. Buildings, mostly limestone Cement, concrete, mortar
10C: Sedimentary Rocks
Uses:
Buildings, mostly limestone
Cement, concrete, mortar
Halite: salt roads, animals licks, medicines
Chalk: black boards, athletes, polishing creams, toothpaste
Pyramids made of limestone

21. Facet’s of earth science: Careers [p.226]
10C: Sedimentary Rocks
Facet’s of earth science: Careers [p.226]
Read Facet
Be able to explain what a sedimentologist is/does

22. 10D: Metamorphic Rocks
Metamorphic rocks: once igneous, sedimentary or even other metamorphic rocks that have chemically and physically changed over time (In 10A notes)
Source rocks: original rocks
Agents of metamorphism: temperature, pressure, hydrothermal fluids

23. 10D: Metamorphic Rocks
Types of Metamorphism:
Regional Metamorphism: rocks changed by the subducting / pressure from plates moving.
Occur over large areas
Main factor: Pressure