Rocks & The Rock Cycle Earth Science Fall 2013

Vocabulary Batholith- intrusive formation with at

least a surface exposure of 100 square kilometers and reaching a depth of thousands of meters

Vocabulary Breccia- elastic sedimentary rock

composed of angular fragments

Vocabulary Cementation- process in which

dissolved minerals left by water passing through sediments bind sediments together

Vocabulary Chemical sedimentary rock- rock

formed from minerals that precipitate out of water

Vocabulary Clastic sedimentary rock- rock made

up of fragments from pre-existing rocks

Vocabulary Compaction- process in which air and

water are squeezed out of sediments, resulting in the formation of sedimentary rock

Vocabulary Concretion- nodule of rock with a

different composition from that of the main rock body

Vocabulary Conglomerate- sedimentary rock

composed of rounded gravel or pebbles cemented together by minerals

Vocabulary Contact metamorphism- change in

the structure and mineral composition of rock surrounding an igneous intrusion

Vocabulary Dike- igneous intrusion that cuts

across rock layers

Vocabulary Evaporites- sedimentary rocks

formed from minerals left after water evaporates

Vocabulary Extrusive igneous rock- rock formed

from molten lava that hardens on the earth’s surface

Vocabulary Foliated- describing metamorphic

rock with parallel bands

Vocabulary Fossil- trace or remains of a plant or

an animal in sedimentary rock

Vocabulary Igneous rocks- rock formed from

cooled and hardened magma

Vocabulary Intrusive igneous rock- rocks formed

from the cooling of magma beneath the earth’s surface

Vocabulary Laccolith- flat-bottomed intrusion

that pushes overlying rock layers into an arc

Vocabulary Lava Plateau- raised flat-topped area

made of layers of hardened lava

Vocabulary Metamorphic rock- rock formed from

other rocks as a result of intense heat, pressure, and chemical processes

Vocabulary Metamorphism- changing of one type

of rock to another by heat, pressure, and chemical processes

Vocabulary Nonfoliated- describing a

metamorphic rock without parallel bands

Vocabulary Organic sedimentary rock- rock

formed from the remains of organisms

Vocabulary Porphyritic- describing an igneous

rock composed of both large and small crystals

Vocabulary Regional metamorphism-

metamorphism that affects rocks over large areas during period of tectonic activity

Vocabulary Rock cycle- series of processes in

which rock changes from one type to another

Vocabulary Sediment- fragments that result from

the breaking of rocks, minerals, and organic matter

Vocabulary Sedimentary rock- rock formed from

hardened deposits of sediment

Vocabulary Sill- sheet of hardened magma that

forms between and parallel to layers of rock

Vocabulary Stock- igneous intrusion with an area

less than 100 square kilometers

Vocabulary Stratification- layering of

sedimentary rock

Vocabulary Volcanic neck- solidified central vent

of a volcano

Rocks & the Rock Cycle Magma from the earth’s interior is

the parent material for all rocks From the time magma cools &

hardens at or near the surface of the earth, the resulting rock begins to change.

Geologists have classified rocks into 3 major types based on the way the rocks are formed.

Rocks & the Rock Cycle 3 major rock types

Igneous rock Sedimentary rock Metamorphic rock

Rocks & the Rock Cycle

Igneous Rocks 2 groups of igneous rocks that are

classified according to where molten rock cools and hardens

Intrusive igneous rocks Magma cools below the crust

Extrusive igneous rocks Rapid cooling of lava on the earths surface

Igneous Rocks Extrusive & intrusive igneous rocks

differ mainly in their sized of crystalline grain and is known as texture

Texture is determine by the cooling rate of the magma or lava that formed the rock

Texture of Igneous Rocks Slow loss of heat allows minerals to form

large, well-developed crystalline grains Coarse-grained texture Ex: granite

Rapid loss of heat does not allow time for large crystalline grains to form, this produces fine-grained rock

Ex: basalt Oceanic crust is made mostly of basalt

Texture of Igneous Rocks Lava or magma cools slowly at first &

then rapidly as it near the earth’s surface, relatively large crystals embedded within a mass of smaller ones

Porphyritic Highly viscous, silica-rich magma

cools rapidly and no crystals form Ex: obsidian

Texture of Igneous Rocks Magma that contains large amounts

of dissolved gases hardens, the gases become trapped in the rock and produces rock full of holes

Ex: pumice

Mineral Composition of Igneous Rocks

Determined by the chemical composition of the magma from which the rock develops

Divided into 3 families Felsic Intermediate Mafic

Mineral Composition of Igneous Rocks

Felsic rocks Formed from magmas that are high in

silica Have light coloring of their main mineral

components, orthoclase feldspar & quartz

May also contain plagioclase feldspar, biotite mica, & muscovite mica

Ex: granite , rhyolite, obsidian Obsidian may be black, blue, or red

depending on its chemical composition

Composition of Igneous Rocks

Mafic rocks Form from magmas that are low in silica

but rich in iron and magnesium Also can include ferromagnesian

minerals making them dark in color Ex: basalt , gabbro

Composition of Igneous Rocks

Intermediate Rocks Medium colored Contain minerals such as plagioclase

feldspar, hornblende, pyroxene minerals, biotite mica

Contain less quartz than the felsic family Ex: diorite , andesite

Igneous Rock Structures Intrusions

Largest of all intrusions are batholiths Form cores of several major mountain ranges like the

Sierra Nevada range in CA & the Coast Range in BC A stock is similar to a batholith only much

smaller Laccoliths form when magma flows between

rock layers and spread upward sometimes pushing the overlying rock into an arc

Frequently found in groups Ex: Black Hills

Igneous Rock Structures Sills form when a sheet of magma flows

between layers of rock and hardens, it does not cause the arcing like a laccolith

Lie parallel to rock layers & vary in thickness from a few cm to hundreds of meters

Ex: Big Bend National Park in Texas When magma forces its way through

rock layers by following existing vertical fractures or by creating new ones and solidifies is called a dike

Common in areas of volcanic activity

Igneous Rock Structures Extrusions

A volcano is a cone of extrusive rock surrounding a central vent, when a volcano stops erupting for a long period the cone gradually wears away and the solidified central vent is left, this is called a volcanic neck

A lava plateau develops from lava that flows out of long cracks in the earth’s surface

Sedimentary Rocks Sedimentary rock is made up of

accumulations of various types of sediments

Compaction & cementation are 2 processes that form sedimentary rocks

Sedimentary rocks are classified according to the kind & size of sediments that form them

Formation of Sedimentary Rocks

Clastic sedimentary rock is made up of rock fragments carried away from their source by water, wind, or ice & left as deposits elsewhere

Chemical sedimentary rock forms from minerals that precipitate from water

Organic sedimentary rock forms from the remains of organisms

Clastic Sedimentary Rocks Classified by the size of the

sediments they contain Conglomerate- rock composed of

rounded gravel sized fragments or pebbles

Breccia- rock made of rock fragments that are angular & have sharp corners

In both conglomerate and breccia the fragments can be easily viewed

Clastic Sedimentary Rocks Sandstones- rocks that are made up of

sand sized grains that have been cemented together

Quartz is the major component Many have pores between the sand grains

through which liquids can move Shale- rock that consists of clay-sized

particles cemented and compacted under pressure

Usually pressed into flat layers that will easily split apart

Chemical Sedimentary Rocks

Form from dissolved minerals that were once dissolved in water

Evaporites- rocks formed from the dissolved minerals left behind from water evaporating

Ex: gypsum & halite Bonneville Salt Flats, Utah

Organic Sedimentary Rocks Rocks formed from the remains of living things

Ex: coal & some limestones Coal forms from decayed plant remains that

are buried and compacted into matter that is mostly carbon

Organic limestones- from marine animal shells Chalk- made up of tiny, one-celled marine

organisms Originally forms as mud on the ocean floor Ex: white cliffs of Dover, England

Sedimentary Rock Features Stratification

Layering of sedimentary rock that occurs when there is a change in the kind of sediment being deposited

Type of deposit varies for many reasons Layers vary in thickness

Grade bedding- occurs when various sizes and kinds of materials are deposited within one layer

Sedimentary Rock Features Ripple Marks & Mud Cracks

Ripple marks are formed by the action of wind or water on sand

Mud cracks result when muddy deposits dry and shrink; the shrinking causes the dried mud to crack

Sedimentary Rock Features Fossils

Remains or traces of ancient plants and animals Usually preserved in sedimentary rock

Concretions Lumps of rock with a different composition from

the main rock body Form when minerals precipitated from solutions

build up around an existing rock particle Groundwater sometimes deposits dissolved

quartz or calcite inside cavities of sedimentary rock where it crystallizes and forms a geode.

Metamorphic Rock Metamorphism is the changing of

one type of rock to another by heat, pressure, and chemical process

Most forms deep beneath the surface of the Earth

All is formed from existing igneous, sedimentary, or metamorphic rock

Formation of Metamorphic Rock

During metamorphism certain minerals change into other minerals; some minerals change in size or shape or separate into parallel bands that give the rock a layered appearance

Formation of Metamorphic Rock

2 types of metamorphism occur in the earth’s crust

Contact metamorphism occurs when rocks come into direct contact with or very near magma

Regional metamorphism occurs due to heat and pressure created by tectonic activity

Most metamorphic rock is formed by regional metamorphism, however rocks formed by contact metamorphism can also be found where regional metamorphism has occurred.

Classification of Metamorphic Rocks Classified according to their texture

into two categories Foliated- have parallel bands of minerals Non-foliated- do not have parallel bands

of minerals

Classification of Metamorphic Rock Foliated Rocks

Form in 2 ways Extreme pressure may flatten the mineral crystals in

the original rock & push them into parallel bands Minerals of different densities separate into bands,

producing a series of alternating dark and light Ex: slate, schist, gneiss

Slate- formed by pressure acting on shale Schist- formed when a greater amount of heat &

pressure change slate into a coarser-grained rock Gneiss- greatly metamorphosed rock with bands of

light and dark minerals

Nonfoliated Rocks Do not have bands of crystals Quartzite- forms when sandstone

undergoes metamorphosis Heat & pressure cause the mineral

grains to recrystallize so that the spaces between them disappear

Marble- formed from the compression of limestone