Lecture 16 Rocks

Igneous Rocks

Formed from molten magma (= lava at the
Earth’s surface)
• Intrusive or plutonic igneous rocks cool
slowly far below Earth’s surface. Mineral
crystals have time to grow big.
• Extrusive or volcanic igneous rocks cool
quickly at or near the Earth’s surface.
Mineral crystals quench quickly and are
small (microscopic) in size.

Classification

Types of igneous rocks

Course texture: Granite (light color), Diorite (intermediate color), Gabbro, (dark color)

Fine-grained texture: Rhyolite (light color), Andeste (intermediate color), Basalt (dark color)

Sedimentary rocks

Sediment may be either:
– Clastic: detrital (rock fragments)
– Non-clastic: chemically deposited
• Characteristics of sedimentary rocks
– Usually layered
– Often contain fossils

Types of sedimentary rocks

mud-sized: shale [calstic], limestone [noncalstic]

sand-sized: sandstone [calstic], rock gypsum [noncalstic]

gravel-size: conglomerate [calstic]

Metamorphic rocks

Formed by changing any rock type by the addition of heat and/or pressure

Metamorphic Rock Classification
– Non-foliated (recrystallized)
• Limestone - Marble
• Sandstone - Quartzite
– Foliated (layered)
• Fine-grained- Slate - Schist
• Coarse - Grained rock - Gneiss

When is the last time a rock on Earth has remained unchanged?

4.5 Ga

Dissolution

minerals that dissolve in chemical weathering

Erosion

Erosion is the process of removing
unconsolidated Earth material and
transporting it to other depositional sites on
land and in the oceans
• Wind, water, ice, and gravity are transport
agents
• Erosion rates depend on climate, relief, and
degree of weathering

Water Abrasion (weathering)

Water and particles are carried actively in water
weather (physically) earth materials
– Chemical ions in water also chemically weather
earth materials

Key elements of the rock cycle

weathering, erosion, and sedimentation