Earth Science Tarbuck/Lutgens

Earth Science Rocks: Earth’s Materials Chapter 3

Chapter-3 Rocks Pretest Describe the strength of bonds between atoms in a solid. What is a mineral? True or False: Only eight elements make up the bulk of the minerals found in Earth’s crust. What is the most common mineral group? What are rock-forming minerals? What are some common properties of minerals?

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 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 Earth as a system: the rock cycle Sediment Sedimentary rock Lithification Sedimentary rock Metamorphism Metamorphic rock Melting Magma

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 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 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 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 texture

Coarse-grained igneous texture

Porphyritic igneous texture

Obsidian exhibits a glassy texture

Composition 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 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 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 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 Magma How Rocks Melt Fractional Crystallization Process wherein different minerals form at different temperatures

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 series

Origins 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 igneous rocks

Classification of 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

Granite

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

Igneous rocks Naming igneous rocks Other compositional groups Andesitic (or intermediate) Ultramafic

End of Chapter 3 Sections 1 & 2