Rocks and the Rock Cycle

Rocks are made of one or more minerals. Each rock belongs to one of three major types; based on how it is formed.

Rock Types

 

1.   __________________________

 

2.   __________________________

 

3. __________________________

Igneous Rocks

• Deep inside the earth, high temperatures melt minerals to form magma.

• When magma rises and cools it forms igneous rocks.

Why does magma rise in the crust?

Hot magma has lower density than the surrounding cooler rock.

Sedimentary Rocks

• On the surface of the Earth, wind and water carry away pieces of rocks, minerals, and the remains of organisms.

• These particles settle to form layers, which get compacted over time.

• Over even longer time the sediments compact, cement together, and hardens into sedimentary rocks.

Metamorphic Rocks

• Through processes of the Earth, rock gets buried. (uplift and subduction)

• Heat and pressure inside the earth can change any type of rock into metamorphic rocks.

• The original rock changes in appearance, structure, and composition.

• Metamorphic rocks DO NOT melt when they change! (no melting here)

The Rock Cycle

The Rock Cycle

Igneous Rocks

The cooling and solidifying of liquid molten material produce igneous rocks. Igneous rocks can be formed inside the Earth or on the surface.

Two Types of Igneous Rocks

1. Extrusive – lava on the surface of the earth solidifies to form rock.

Examples: rhyolite, basalt, pumice (fine grain)

2. Intrusive – magma solidifies beneath the surface of the earth to form rock.

Examples: granite, gabbro (coarse grain)

(use page 6 ESRT for examples)

Lava vs. Magma

Lava

• Molten rock on the surface

• Cools quickly

• extrusive

Magma

• Molten rock below the surface

• Contains dissolved gasses

• Cools slowly

• intrusive

Factors that effect magma formation…

1. Temperature – higher temps. allow minerals to melt.

2. Pressure – higher pressures actually slow the process of melting, requiring more heat.

3. Water content – the presence of water allows minerals to melt at a lower temp.

How magma forms…

• Different minerals melt at different temperatures.

• Partial melting occurs – process whereby some minerals melt at lower temps, while other minerals remain solid (slushy mix)

• Different minerals crystallize at different temperatures.

• Fractional crystallization occurs – reverse order of partial melting, with minerals crystallizing.

Bowen’s Reaction Series

• Different minerals will form at different temperatures, because newly formed crystals react with the magma.

Magma types

Basaltic

Andesitic

Rhyolitic

Early, high temps (~1000ºC)

Late, low temps (~600ºC)

Olivine

Pyroxene

Amphibole

Biotite Mica

Ca rich

Na rich

Magma Types

• Basaltic

• Andesitic

• Rhyolitic

Igneous Rock Identification

Igneous Rock are identified by texture and mineral composition.

Texture – depends on how fast the magma or lava cools.

• Coarse-grained – large visible grains (slow cooling)

• Fine-grained – very small grain size, may need a microscope to see (fast cooling)

• Glassy texture – no grains visible (cooled extremely fast, also know as quenched)

• Porphyritic texture – large grains embedded in fine-grained rocks (cooled slow, then fast)

• Vesicular – contains many holes (formed with gas bubbles in material when cooling)

Composition – the minerals contained in each rock.

• Mafic – contains mostly darker colored minerals (% of composition)

Examples:

• Felsic – contains mostly lighter colored minerals (% of compostion)

Examples: