Rocks:

Sedimentary, Igneous, and Metamorphic

What are Sedimentary Rocks?

  • Rocks formed from accumulated sediments
  • Make up about 75% of rocks at Earth's surface
  • Record Earth's history like pages in a book
  • Form in layers called strata

Three Main Types

  1. Clastic (from rock fragments)

    • Formed from weathered rock pieces
    • Examples: sandstone, shale

  2. Chemical (from precipitation)

    • Formed from dissolved minerals
    • Examples: rock salt, some limestones

  3. Organic (from living things)

    • Formed from plant/animal remains
    • Examples: coal, some limestones

The Formation Process

  1. Weathering breaks down rocks
  2. Erosion moves particles
  3. Deposition lays down sediments
  4. Compaction squeezes sediments
  5. Cementation binds particles together

Clastic Sedimentary Rocks

Based on particle size (largest to smallest):

  • Conglomerate (rounded pebbles)
  • Breccia (angular fragments)
  • Sandstone (sand grains)
  • Siltstone (silt particles)
  • Shale (clay particles)

Chemical Sedimentary Rocks

Form when minerals precipitate from solution:

  • Rock salt (evaporation)
  • Travertine (hot springs)
  • Some limestones (marine precipitation)

Key process: Evaporation or Chemical Precipitation

Organic Sedimentary Rocks

Formed from remains of organisms:

  • Coal (plant material)
  • Chalk (microscopic shells)
  • Reef limestone (coral remains)

Key process: Accumulation and Preservation of organic matter

Importance of Sedimentary Rocks

  • Contain fossils -> Earth's history
  • Hold oil and gas deposits
  • Major building materials
  • Form aquifers for groundwater
  • Record ancient environments

Questions to Consider

  1. Why are sedimentary rocks usually found in layers?
  2. How can we use sedimentary rocks to learn about past environments?
  3. Why are fossils almost always found in sedimentary rocks?
  4. How do human activities impact sedimentary processes today?

Lab Review

Review Rocks and Classification

  1. Get your rock bag
  2. Put them back in order
  3. We will review as a class (some bags have slighly different rocks)

Yes, I got some wrong yesterday, lets fix that

it is okay to be wrong sometimes, we learn from that

Formation (ESRT page 6):

center

Lab Review

Formation Methods:

  1. Clastic Rocks:
    • Weathering & Erosion -> Deposition and Burial -> Compaction and/or Cementation
  2. Crystalline:
    • Chemical Formation: Minerals dissolve in water -> solution becomes concentrated -> crystals grown and accumulate -> compaction and cementation occurs
  3. Organic:
    • Organisms die and are buried -> material is compressed -> some recrystalization may occur -> C&C occurs

Igneous Rocks

Formation, Types, and Classification

What are Igneous Rocks?

  • Formed from cooling and crystallization of magma or lava
  • Name comes from Latin "ignis" meaning fire
  • Make up most of Earth's crust
  • Can form both underground and at the surface

Two Main Categories

  1. Intrusive (Plutonic)
    • Forms underground
    • Slow cooling → large crystals
    • Examples: granite, gabbro
  2. Extrusive (Volcanic)
    • Forms at the surface
    • Rapid cooling → small crystals or glass
    • Examples: basalt, obsidian

The Formation Process

  1. Rock melts due to:

    • Increased temperature
    • Decreased pressure
    • Addition of volatiles

  2. Magma rises due to:

    • Lower density than surroundings
    • Pressure differences
    • Tectonic activity

  3. Crystallization occurs as magma cools

Composition of Igneous Rocks

Classified by silica content:

  • Felsic (>65% silica)

    • Light-colored
    • Lower density
    • Example: granite

  • Mafic (<50% silica)

    • Dark-colored
    • Higher density
    • Example: basalt

Important Igneous Rocks

Intrusive:

  • Granite, Diorite, Gabbro, Peridotite

Extrusive:

  • Basalt, Obsidian, Pumice, Rhyolite

center

Importance of Igneous Rocks

  • Form new crustal material
  • Create valuable mineral deposits
  • Build volcanic islands
  • Provide geothermal energy
  • Create fertile soils
  • Source of building materials

ESRT Page 6: Igneous Rocks

center

Igneous vs. Sedimentary Rocks: A Comparison

Igneous Rocks:

  • Form from cooling magma/lava
  • Interlocking crystals
  • No layers or fossils
  • Form primarily through heat
  • Can form deep underground or at surface

Sedimentary Rocks:

  • Form from accumulated sediments
  • Cemented particles or precipitates
  • Occur in layers
  • Contain fossils
  • Form at Earth's surface or shallow depths

The Rock Cycle

What is the Rock Cycle?

The rock cycle is the continuous process through which:

  • Earth materials change form
  • Rocks transform from one type to another
  • Matter and energy flow through Earth systems

ESRT: page 6

Three Major Rock Types

Igneous Rocks

  • Formed from cooling magma or lava
  • Examples: granite, basalt

Sedimentary Rocks

  • Formed from compressed sediments
  • Examples: sandstone, limestone

Metamorphic Rocks

  • Formed when existing rocks are changed by heat and pressure
  • Examples: marble, schist

Driving Forces of the Rock Cycle

The rock cycle is powered by:

  1. Earth's Internal Heat

    • Drives plate tectonics
    • Creates magma

  2. Solar Energy

    • Drives the water cycle
    • Powers weather and erosion

  3. Gravity

    • Causes materials to move downhill
    • Compacts sediments

Processes in the Rock Cycle

Constructive Processes:

  • Volcanism
  • Mountain building
  • Crystallization
  • Cementation
  • Recrystallization

Destructive Processes:

  • Weathering (physical & chemical)
  • Erosion
  • Melting
  • Dissolution

Igneous Rocks in the Cycle

Formation:

  1. Melting of existing rock
  2. Cooling and crystallization

Pathways:

  • To Sedimentary: Weathering -> Erosion -> Deposition
  • To Metamorphic: Heat + Pressure (without melting)

Sedimentary Rocks in the Cycle

Formation:

  1. Weathering of existing rock
  2. Transport & deposition
  3. Compaction & cementation

Pathways:

  • To Igneous: Deep burial -> Melting
  • To Metamorphic: Heat + Pressure

Examples in New York State:

  • Devonian shales of Finger Lakes region
  • Potsdam Sandstone

Metamorphic Rocks in the Cycle

Formation:

  1. Subjecting existing rock to heat and pressure
  2. Recrystallization without melting

Pathways:

  • To Igneous: More heat → Melting
  • To Sedimentary: Uplift → Weathering → Erosion → Deposition

Examples in New York State:

  • Manhattan Schist
  • Adirondack marble and gneiss

New York State Rock Cycle Evidence

  • Adirondack Mountains

    • Metamorphic core
    • Sedimentary rock borders

  • Catskill Mountains

    • Sedimentary rocks (sandstone, shale)
    • Evidence of ancient river deltas

  • Hudson Highlands

    • Metamorphic rocks exposed by erosion

Rates of Change

Rock cycle processes occur at different timescales:

Rapid (human timescale)

  • Volcanic eruptions
  • Landslides
  • Floods

Gradual (geologic timescale)

  • Mountain building
  • Metamorphism
  • Most sedimentary rock formation

Human Impacts on the Rock Cycle

Humans accelerate or alter natural processes:

  • Mining and quarrying
  • Construction and land use changes
  • Acid rain and pollution effects
  • Dam construction changing sediment transport
  • Climate change affecting weathering rates