Earth Science
Tarbuck/Lutgens
Earth ScienceEarth Science
Rocks:
Earth’s
Materials
Chapter 3
Chapter-3 Rocks PretestChapter-3 Rocks Pretest
1. Describe the strength of bonds between atoms in a solid.
2. What is a mineral?
3. True or False: Only eight elements make up the bulk of the minerals found in Earth’s crust.
4. What is the most common mineral group?
5. What are rock-forming minerals?
6. What are some common properties of minerals?
Rocks Rocks
A rock is any solid mass of mineral or mineral-like matter that occurs naturally as part of our planet.Some rocks are composed of one mineral,
however most rocks are a solid mixture of many minerals.
The three major types of rocks are igneous rocks, sedimentary rocks, and metamorphic rocks.
Rock cycle Rock cycle
Shows the interrelationships among the three rock types.It shows that interactions among Earth’s
water, air, and land can cause rocks to change from one type to another.
Earth as a system: the rock cycle • Magma
• Crystallization of magma or lava
• Igneous rock • Weathering, transportation, and deposition
Rock cycle Rock cycle
Earth as a system: the rock cycle • Sediment
• Lithification
• Sedimentary rock • Metamorphism
• Metamorphic rock • Melting
• Magma
Rock cycle Rock cycle
Earth as a system: the rock cycle • Full cycle does not always take place due to
“shortcuts” or interruptions (alternate paths)• e.g., Sedimentary rock melts • e.g., Igneous rock is metamorphosed • e.g., Sedimentary rock is weathered • e.g., Metamorphic rock weathers
The
Rock Cycle
Igneous rocksIgneous rocks
Form as magma cools and crystallizes • Rocks formed inside Earth
are called plutonic or intrusive rocks
• Rocks formed on the surface
• Formed from lava (a material similar to magma, but without gas)
• Called volcanic or extrusive rocks
Igneous RocksIgneous Rocks
Igneous rocks Igneous rocks
Crystallization of magma • Ions are arranged into orderly patterns • Crystal size is determined by the rate of
cooling • Slow rate forms large crystals • Fast rate forms microscopic crystals • Very fast rate forms glass
Igneous rocks Igneous rocks
Classification is based on the rock’s texture and mineral constituents • Texture
• Size and arrangement of crystals • Types
• Fine-grained – fast rate of cooling• Coarse-grained – slow rate of cooling • Porphyritic (two crystal sizes) – two rates of
cooling • Glassy – very fast rate of cooling
Fine-grained igneous Fine-grained igneous texturetexture
Coarse-grained igneous Coarse-grained igneous texturetexture
Porphyritic igneous Porphyritic igneous texturetexture
Obsidian exhibits a Obsidian exhibits a glassy textureglassy texture
Composition of MagmaComposition of Magma
• Silica (SiO2) is the most abundant compound found in magma and has the greatest effect on magma characteristics.– Silica content affects:
• Melting temperature• Speed at which magma
flows
Origins of MagmaOrigins of Magma
• Most rocks melt between 800oC and 1200oC– Sources of Earth’s heat
comes from:• Earth’s formation
• Radioactive elements
• Gravitational pull
• Factors affecting magma formation– Temperature
• Temperature increases with depth
Origins of MagmaOrigins of Magma
• Factors affecting magma formation (continued)– Pressure
• Pressure increases with depth
• As pressure increases, its melting point also increases
– Water Content• As water content
increases, the melting point decreases
– Mineral Content• Different minerals have
different melting points
Origins of MagmaOrigins of Magma
• How Rocks Melt– Partial Melting
• Process whereby some minerals melt at low temperatures while others remain solid
– Magma chemistry can change if it partially melted
Origins of MagmaOrigins of Magma
• How Rocks Melt– Fractional Crystallization
• Process wherein different minerals form at different temperatures
Igneous rocks Igneous rocks
Classification is based on the rock’s texture and mineral constituents • Mineral composition
• Explained by Bowen’s reaction series which shows the order of mineral crystallization
• Influenced by crystal settling in the magma
Bowen’s reaction seriesBowen’s reaction series
Origins of MagmaOrigins of Magma
• Crystal Separation– Occurs when crystals settle
to the bottom of the magma body, or when liquid magma is separated from the magma body
• Layered Intrusions– In some magma bodies,
the minerals form into distinct bands in the order shown in Bowen’s Reaction Series
Classification of Classification of igneous rocksigneous rocks
Classification of Classification of igneous rocksigneous rocks
Igneous rocks Igneous rocks
Naming igneous rocks • Granitic rocks
• Composed almost entirely of light-colored silicates – quartz and feldspar
• Also referred to as felsic: feldspar and silica (quartz)
• High silica content (about 70 percent) • Common rock is granite
GraniteGranite
Igneous rocks Igneous rocks
Naming igneous rocks • Basaltic rocks
• Contain substantial dark silicate minerals and calcium-rich plagioclase feldspar
• Also referred to as mafic: magnesium and ferrum (iron)
• Common rock is basalt
Basalt Basalt
Igneous rocks Igneous rocks
Naming igneous rocks • Other compositional groups
• Andesitic (or intermediate) • Ultramafic
End of Chapter 3End of Chapter 3Sections 1 & 2Sections 1 & 2