Science - Module 4: Different Rocks and the Rock Cycle

Igneous rocks

Rocks formed from the cooling and crystallization of magma or lava

Sedimentary rocks

Rocks formed from the accumulation and compaction of sediments

Metamorphic rocks

Rocks that have been changed by heat, pressure, or chemically active fluids

Rock cycle

The process of rocks forming, changing, being destroyed, and reforming

Magma

Molten rock located underground

Lava

molten rock that reaches the surface

How to determine Igneous Rock

Magma's composition determines the type of igneous rock, specifically the amount of silica.

Magma types

Basaltic (low silica), Andesitic (medium), Rhyolitic (high silica).

Factors affecting magma formation

Temperature, Pressure, Water Content, Mineral Content.

Effect of water on melting point

More water lowers the melting point of rocks.

Fractional crystallization

The first minerals to crystallize are the last to melt

Intrusive rock

Magma cooled underground resulting in large crystals (coarse-grained)

Extrusive rock

Lava cooled at the surface resulting in small crystals (fine-grained)

Felsic rocks

Light color, high silica & feldspar (example: granite

Mafic rocks

Dark, rich in magnesium and iron (example: basalt)

Intermediate rocks

Rocks that are between felsic and mafic (examples: andesite, diorite)

Coarse-grained

Rocks with large crystals formed from slow cooling

Fine-grained

Rocks with small crystals formed from fast cooling

Glassy

Rocks with no crystals (example: obsidian)

Porphyritic

Rocks with large crystals in a fine background

Vesicular

Rocks with a spongy texture and gas holes (examples: pumice, scoria)

Veins in igneous rocks

Intrusions that may contain ore

Pegmatites

Large-crystal veins, sometimes containing valuable minerals

Weathering

Physical and chemical processes that break rock into smaller pieces

Sediments

Small rock pieces moved by water, wind, glaciers, or gravity

Physical weathering

Rocks broken into smaller pieces without changing composition

Chemical weathering

Minerals dissolve or chemically change

Erosion

Removal and transport of sediment

4 main agents of erosion

wind, water, gravity, glaciers

Deposition

Sediments settle out and form layers

Particle settling in water

Larger particles sink first, finer ones remain on top

Lithification

Processes that turn sediments into rock

Lithification processes

compaction and cementation

Compaction

The process of sediments being pressed together under pressure

Weight of overlying sediments

Reduces volume/porosity

Clastic sedimentary rocks

Formed from deposits of loose sediments

Classification of clastic rocks

By particle size: coarse, medium, fine

Conglomerate

Coarse rock with rounded fragments

Breccia

Coarse rock with angular, sharp fragments

Sandstone

Medium-grained rock made of cemented sand

Porosity

Percent of open space between grains

Shale

Fine-grained rock of compacted clay with low porosity

Formation of chemical sedimentary rocks

From minerals that precipitate or evaporate from water

Evaporites

Rocks formed when water evaporates, leaving minerals behind

Biochemical sedimentary rocks

Form from remains of living things

Most abundant biochemical rock

Limestone

Formation of coal

From ancient plants in swampy areas; made mostly of carbon

Metamorphism

Process where rock changes into metamorphic rock due to heat and pressure

Source of heat and pressure for metamorphism

Deep burial

Mineral changes during metamorphism

They change into other minerals (solid-state alterations)

Foliated texture

Mineral grains arranged in bands due to heat and pressure

Reason foliated rocks break along bands

Chemical bonds are weaker where bands occur

Examples of foliated rocks

slate, schist, gneiss

Nonfoliated texture

Mineral grains not arranged in bands, crystals are blocky

Strength of nonfoliated rocks

They don't contain aligned mineral bands

Examples of nonfoliated rocks

Marble, Quartzite, Hornfels

Regional metamorphism

Large-scale changes from heat & pressure, usually at plate boundaries. Most metamorphic rocks form this way

Contact metamorphism

Local changes when rock touches magma. Effects decrease with distance

Hydrothermal metamorphism

Hot water reacts with rock, altering composition and forming ore deposits