Download 3 - Classifying Rocks

Unit 3: Earth Materials
Lesson 3: Classifying Rocks
(Heath Earth Science pg. 62-78)
Today’s Objectives
 Differentiate between rocks and minerals,
including:
 Classify rocks as igneous, sedimentary, or
metamorphic using texture and composition
 Describe the relationship between crystal size and
cooling rate in igneous rocks
 Classify igneous rocks as volcanic (extrusive) or
plutonic (intrusive) on the basis of texture
Review
 Last day we learned the 3 main types of rocks, and how these
rocks are formed in the rock cycle
 The 3 rock types are:
Igneous
Sedimentary
Metamorphic
 Today, we will look more closely at these rock types and how
to identify them
The
Rock
Cycle
Igneous Rocks
 Igneous rocks are formed by the cooling and hardening of hot
molten rock from inside of the earth
 This hot molten rock is called magma
 When magma reaches the surface of the earth during a volcanic eruption
it is called lava
 When magma cools, elements in it form distinct, interlocking mineral
grains, or crystals
 There are two general types of magma:
 Felsic (granitic) magma: high % silica (SiO2); thick, slow flowing;
forms light-coloured minerals/rocks
 Mafic (basaltic) magma: low % silica; hotter, thinner, fast flowing;
forms dark-coloured minerals/rocks
Igneous Rocks
 Rocks that form underground from cooled magma are called
plutonic, or intrusive, igneous rocks
 These rocks are only seen at the surface after the rock that
covers them is worn away
 These rocks tend to have large mineral grain (crystal) size
because the magma cools more slowly beneath the surface
 Rocks that form on the surface from cooled lava are called
volcanic, or extrusive, igneous rocks
 These rocks tend to lack, or have very small mineral grains
because they cool very rapidly
Igneous Rock Textures
 A rock’s texture depends on the size, shape, and arrangement
of it’s mineral grains, or crystals
 Glassy Texture:
 produced by very rapid cooling
 No visible grains
 Fine-grained texture:
 Produced when lava cooled quickly on or near Earth’s surface
 Small grains
 Porphyritic texture:
 Produced by slow then rapid cooling
 Has both fine and coarse grains
 Coarse-grained texture:
 Produced when magma cools slowly at depth
 Large (coarse) grains
Grain size and Cooling Rate
Igneous Rocks
Glassy Textures
Igneous Rocks
Classifying Igneous Rocks
Practice:
 Topic Questions: Page 68, #3-8
Sedimentary Rocks
Sedimentary Rocks
 Sedimentary rocks form when sediments harden into rocks
 There are three main kinds of sedimentary rocks:
 Clastic (Detrital):
 Formed from fragments of other rocks
 Ex.) shale, sandstone, conglomerate
 Chemical:
 Formed from mineral grains that fall out of a solution (precipitate) by
evaporation or chemical action
 Ex.) rock salt, limestone
 Organic:
 Formed from the remains of plants and animals
 Ex.) coal, limestone made of shell fragments (coquina)
Sedimentary Rocks
Clastic Sedimentary Rocks: Conglomerate (top left), Breccia
(bottom left), Shale (right)
Sedimentary Rocks
Clastic Sedimentary
Rock: Sandstone
Organic Sedimentary Rock:
Coquina
Sedimentary Rocks
Chemical Sedimentary Rocks
Limestone
Rock Salt
Sedimentary Rock Features
 The origin of some sedimentary
rock can be discovered by observing
certain features
 Ripple marks indicate the rock
was formed under water moving
water or on a beach
 Mud cracks indicate the rock was
formed from mud that dried and
shrunk, such as on a tidal plain or
desert
Sedimentary Rock Features
 Cross bedding may develop when beds are deposited by
wind on sand dunes or deposited by rivers on deltas or
sandbars
 Sedimentary rocks with visible layers are said to be
stratified
Classifying Sedimentary Rocks
Practice:
 Topic Questions: page 74-75, #9-17
Metamorphic Rocks
Metamorphic Rocks
 Metamorphic rocks are formed when igneous rocks,
sedimentary rocks, or even other metamorphic rocks are
altered due to intense heat and/or pressure
 There are two kinds of metamorphism:
 Regional metamorphism
 occurs when large areas of rock are under intense heat and pressure that
causes them to change form
 Contact metamorphism
 occurs when hot magma forces its way into overlying rock and bakes the
rocks that are in contact with it
 Much smaller scale than regional metamorphism
Metamorphism
Results of Metamorphism
 Under the pressure of metamorphism, some mineral grains in
the parent rock become reoriented and aligned at right
angles to the stress
 The resulting orientation of mineral grains gives the rocks a
foliated (layered) texture
 Some rocks are under pressure from more than one direction
(differential stress) that they may produce folds (such as the
rocks on the first slide of metamorphic rocks)
Foliation
Foliated and Non-Foliated Rock
Classifying Metamorphic Rocks
Practice:
 Topic Questions: page 79, #19-23
Homework
 Create a rock cycle diagram/rock description according to
the provided rubric
 One page diagram
 One page describing 3 examples of each rock type with all the
classification information
 Due date: Monday, December 29
 Mineral Identification Quiz next class!