Chapter 4: Igneous Rocks I Product of Earth's Internal Fire
Chapter 4: Igneous Rocks: Product of Earth’s Internal Fire
ntroduction: What Is an Igneous Rock? gneous rocks vary greatly. Some contain large mineral grains. Others contain grains so small they can barely be seen under a high power microscope. gneous rocks also vary greatly in color. All igneous rocks are formed through the cooling and solidification of magma
Introduction: What Is an Igneous Rock? ◼ Igneous rocks vary greatly. ◼ Some contain large mineral grains. ◼ Others contain grains so small they can barely be seen under a high power microscope. ◼ Igneous rocks also vary greatly in color. ◼ All igneous rocks are formed through the cooling and solidification of magma
Intrusive Versus Extrusive Igneous rocks Intrusive igneous rocks form when magma cools within existing rocks in Earth's crust a Extrusive igneous rocks form when magma cools on Earths surface, where they have been“ extruded
Intrusive Versus Extrusive Igneous Rocks ◼ Intrusive igneous rocks form when magma cools within existing rocks in Earth’s crust. ◼ Extrusive igneous rocks form when magma cools on Earth’s surface, where they have been “extruded
Texture In Igneous Rocks The two most obvious textural features of an igneous rock are the size of its mineral grains and how the mineral grains are packed together. Sizes of mineral grains Intrusive rocks are coarse-grained Magma that solidifies in the crust cools slowly and has sufficient time to form large mineral grains
Texture In Igneous Rocks The two most obvious textural features of an igneous rock are the size of its mineral grains and how the mineral grains are packed together. Sizes of mineral grains: ◼ Intrusive rocks are coarse-grained. ◼ Magma that solidifies in the crust cools slowly and has sufficient time to form large mineral grains
Texture In Igneous Rocks Extrusive rocks are fine-grained a Magma that solidifies on the surface usually cools rapidly, allowing insufficient time for large crystals to grow. a Coarse-grained igneous rock is called a phanerite显晶岩( from the greek word meaning visible)
◼ Extrusive rocks are fine-grained ◼ Magma that solidifies on the surface usually cools rapidly, allowing insufficient time for large crystals to grow. ◼ Coarse-grained igneous rock is called a phanerite 显晶岩(from the Greek word meaning visible). Texture In Igneous Rocks
Texture In Igneous Rocks -Igneous rock that contains unusually large mineral grains(2cm or larger) is called a pegmatite伟晶岩 a Fine-grained igneous rock is called an aphanite隐晶岩( from the greek word meaning invisible
◼ Igneous rock that contains unusually large mineral grains (2cm or larger) is called a pegmatite 伟晶岩. ◼ Fine-grained igneous rock is called an aphanite隐晶岩 (from the Greek word meaning invisible). Texture In Igneous Rocks
Texture In Igneous Rocks The isolated large grains are phenocrysts sf a porphyry is an igneous rock in which 50 or more of the rock is coarse mineral grains scattered through a mixture of fine mineral grains
Texture In Igneous Rocks ◼ The isolated large grains are phenocrysts 斑 晶. ◼ A porphyry is an igneous rock in which 50% or more of the rock is coarse mineral grains scattered through a mixture of fine mineral grains
Texture In Igneous Rocks Glassy rocks Atoms lack time to organize themselves into mineraIs aA mineraloid forms instead(mineral-like solid that lacks either a crystal structure or a definite composition or both) Extrusive igneous rocks that are largely or wholly glassy are called obsidian黑曜石 They display a distinctive conchoidal贝壳状 fracture(smooth, curved surface)
Texture In Igneous Rocks ◼ Glassy rocks. ◼ Atoms lack time to organize themselves into minerals. ◼ A mineraloid forms instead (mineral-like solid that lacks either a crystal structure or a definite composition or both). ◼ Extrusive igneous rocks that are largely or wholly glassy are called obsidian 黑矅石. ◼ They display a distinctive conchoidal 贝壳状 fracture (smooth, curved surface)
Glassy rock, Obsidian from the Jemez mountains
Glassy Rock, Obsidian from the Jemez Mountains
Mineral Assemblage In Igneous Rocks Once the texture of an igneous rock is determined, its name will depend on its mineral assemblage. All common igneous rocks consist largely of ■ Quartz Feldspar (both potassium feldspar and plagioclase). Mica(both muscovite and biotite). ■ Amphibole ■ Pyroxene a Olvine
Mineral Assemblage In Igneous Rocks ◼ Once the texture of an igneous rock is determined, its name will depend on its mineral assemblage. ◼ All common igneous rocks consist largely of: ◼ Quartz. ◼ Feldspar (both potassium feldspar and plagioclase). ◼ Mica (both muscovite and biotite). ◼ Amphibole. ◼ Pyroxene. ◼ Olivine
