Chapter 6 – RocksChapter 6 – RocksSection 6.1 – Rocks and the Rock CycleSection 6.1 – Rocks and the Rock Cycle

Section Objectives

Identify the 3 major types of rock, and explain how each type forms.

Summarize the steps in the rock cycle.

Explain Bowen’s reaction series.

Summarize the factors that affect the stability of rocks.

Rocks Are:

The materials that make up the solid part of the earth.

A collection of one or more minerals, may not be crystals (glass).

3 Major Types of Rocks3 Major Types of Rocks(based by the way the rocks form)(based by the way the rocks form)

Igneous Rock(Latin: “from fire”)

Forms when molten rock (magma) cools and hardens.

Magma is called lava when it is erupted on the Earth’s surface.

Sediments

Agents of erosion (wind, water, ice, gravity) break down all types of rock into small fragments.

These fragments of rocks, crystals, and organic matter are known as sediment.

Satellite Photograph;Rio Tinto, Spain

Sediments DepositedSediments Deposited

Sediments are Sediments are carried away and carried away and deposited in another deposited in another area by wind, water, area by wind, water, and ice. They are and ice. They are then compressed then compressed and/or cemented and/or cemented together to harden together to harden into……..into……..

Sedimentary Rocks

Pressure, Heat, and Chemical Processes

• Can change the form Can change the form of an existing type of of an existing type of rock. The result is rock. The result is an altered rock an altered rock known as………known as………

Metamorphic Rock

Greek: “changed form”Greek: “changed form”

The Rock Cycle

Any rock can be changed into another of the three types of rock.

Rock cycle video

Changed Conditions = Changed Rock

A particular body of rock does not always pass through each stage of the rock cycle.

Properties of Rocks

The physical characteristics of rock reflect the chemical composition of the rock

N. L. Bowen (1928)

Proposed that different minerals form at different times during the cooling of magma, and that they generally form in the same order. The pattern of mineral formation depends on the chemical composition of the magma.

Bowen’s Reaction Series

• Minerals form in one of two ways. The first (right-hand side) is a gradual, continuous formation of plagioclase minerals that have similar chemical compositions.

Zoned Plagioclase:Ca rich core, Na rich rim

The Second Way

• Sudden changes in mineral types, the discontinuous reaction series of Fe-Mg minerals (the left-hand side of the diagram).

Chemical Stability of Minerals

The rate at which a mineral breaks down is dependent on the chemical stability of the mineral, and is a measure of the tendency to maintain its original composition rather than break down to form a different chemical.

Depends on Chemical Bond StrengthDepends on Chemical Bond Strength

Generally, the most Generally, the most resistant minerals resistant minerals have the highest have the highest number of bonds number of bonds between silica and between silica and oxygen. This oxygen. This reflects Bowen’s reflects Bowen’s reaction series (first reaction series (first formed, first formed, first destroyed).destroyed).

Physical Stability of Rocks

Rocks have natural zones of weakness that are determined by how and where the rocks form. Once the surfaces of these weaknesses are exposed to air and water, chemical and physical weathering begins.

Sedimentary RocksSedimentary Rocks

Zones of weakness along layers or through fractures that develop when pressure is released when the rock is uplifted to the Earth’s surface.

Sedimentary rock video

Metamorphic Rocks

Can have layering also, which are zones of weakness.

Metamorphic Rock video

Igneous Rocks

Can have evenly spaced zones of weakness, called joints, that form as the rock cools and contracts.

Igneous rock video

AssignmentAssignment

Significant DigitsSignificant Digits6.1 Key Terms6.1 Key TermsRock Cycle Directed Rock Cycle Directed

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