EARTH SCIENCEROCKS

IGNEOUS, SEDIMENTARY,

AND METAMORPHIC

WHAT IS A ROCK? A rock is a group of minerals that are

bound together. Rocks are MIXTURES because they have

varying percentages of different minerals Rocks are classified according to how they

were formed.

THREE GENERAL TYPES OF ROCKS:

Igneous rocks—formed by the cooling and hardening of magma from inside the earth.

Sedimentary rocks—formed by the compaction and cementing of layers of sediments

Metamorphic rocks—formed by the effects of heat and pressure on other rocks

ROCK CYCLE Rocks form from other rocks. The rock cycle is the repeated series of

events by which rock gradually and continually changes from one type to another.

“WORDY VERSION” OF ROCK CYCLE

Magma (hot, molten rock) beneath the earth’s surface is the source of all rocks.

Once magma reaches the surface (lava), or cools in the interior (as magma) igneous rocks are formed.

Once igneous rocks are weathered and erodedsedimentary rocks are formed.

Sedimentary rocks (and sometimes igneous rocks) are buried and caught in Earth’s movementsmetamorphic rocks are fomed.

“SCHEMATIC” ROCK CYCLE

“VISUAL” ROCK CYCLE

MAGMA Is hot, molten rock beneath Earth’s surface Is called lava once it reaches the surface Four types:

Felsic

Intermediate

Mafic

Ultramafic

FELSIC MAGMA Thick and slow moving Large amounts of silica Hardens into rocks of light-colored silicate

minerals

MAFIC MAGMA Hotter, thinner than felsic Large amounts of iron and magnesium Forms rocks of darker colors

INTERMEDIATE MAGMA Mix between felsic and mafic

Ultramafic Low Si High Fe and Mg Green in color or

green tint Varying densities Kimberlites are rare

ultramafic rocks where diamonds have been found in Kimberly, S Africa

Peridotite

Dunite

IGNEOUS ROCKS

Although all igneous rocks form from magma, they are not all the same.

The differences are caused by: Variations in the magma’s composition Variations in the formation process

Formed from underground magma intrusive Formed at Earth’s surface extrusive

TEXTURE OF IGNEOUS ROCKS

The texture of an igneous rock is caused by the rate of cooling. Cools rapidly extrusive glassy, fine-grained

texture Cools slowly intrusive coarse texture, crystals

formed

Igneous Textures Fine Grained- cools fast,

small crystals form (too small to be seen without the use of a microscope)

Coarse Grained- cools slowly, large visible crystals (easily seen with the eye, many colors or patterns)

Basalt

Granite

Igneous Textures Glassy: cools too fast for

crystals to form.

Porphyritic: mixture of fine and coarse grains. Fine grained ground mass with large crystals mixed in.

Pumice Obsidian

Andesite

Bowen’s Reaction Series A Canadian

scientist, N.L. Bowen, demonstrated that as magma cools, minerals form in predictable patterns.

Each mineral crystallizes at a different temperature.

SEE “Explore” of your Discovery Techbook, Igneous Rocks

FAMILIES OF IGNEOUS ROCKS

Are grouped together based solely on mineral composition, so a family can have rocks of all different textures and origins.

Three main families: Granite Family Gabbro Family Diorite Family

GRANITE FAMILY Form from felsic magmas Usually coarse-grained from slow cooling Usually made of quartz, feldspar, mica, and

hornblende Granite Obsidian Pumice Rhyolite

GRANITE

OBSIDIAN

PUMICE

RHYOLITE

GABBRO FAMILY Mainly made from mafic magma Darker in color and denser than granite

family Gabbro Basalt Scoria

GABBRO

BASALT

SCORIA

DIORITE FAMILY From intermediate magma (characteristics

of felsic and mafic) Color is darker than granites and lighter

than gabbros (dark greys and greens) Diorite andesite

DIORITE

ANDESITE

IGNEOUS INTRUSIONS Are rock masses that form when magma

cools inside Earth’s interior Forces within the earth push magma up

into the bedrock Igneous intrusions are also called plutons

TYPES OF IGNEOUS INTRUSIONS

Dikes—sheet of igneous rock cuts across rock layers vertically or at a steep angle

Sills—sheet of igneous rock that lies parallel to the layers it intrudes

Laccoliths—from stiff magma that does not flow easily—bulges upward to form domed masses

Batholiths—form core of mountain ranges (largest of all intrusions)

SEDIMENTARY ROCKS While most of the earth’s crust is made of

igneous rock, most of the earth’s surface is made of sedimentary rock

Formed from the compaction and cementation of layers of sediments

FAMILIES OF SEDIMENTARY ROCKS

Are grouped according to their formation process

Three general groups in text: Clastic Chemical Organic

CLASTIC ROCKS Are formed from the fragments of other

rocks Conglomerates—the coarsest clastic rocks Sandstones—made of quartz and sand Shales—made of silt and clay

CHEMICAL ROCKS Made when minerals precipitate out of a

solution Rock salt Rock gypsum Some limestones

ORGANIC ROCKS Form from sediments of plant or animal

remains Limestone Coal

LIMESTONE

COAL

FEATURES OF SEDIMENTARY ROCKS

Stratification Fossils Ripple marks Mud Cracks Nodules Concretions geodes

STRATIFICATION The arrangement of visible layers Most apparent characteristic of sedimentary

rocks Line between layers is called bedding

plane Usually horizontal, but cross-bedding can occur

FOSSILS The remains, impression, or any other

evidence of a plant or animal preserved in rock

RIPPLE MARKS Sand patterns formed by the action of

winds, streams, waves, or currents

MUD CRACKS Occurs where a muddy road or puddle of

water has dried out after the rain

Modern Ancient

NODULES Hard lumps of silica in limestone and chalk

CONCRETIONS Round, solid masses of calcium carbonate

in layers of shale

GEODES Spheres of rocks filled with crystals that

occur in limestones

METAMORPHIC ROCKS Formed by the effect of heat and pressure

on other rocks Formed from pre-existing rocks called

parent rocks Usually resemble their parent rocks

METAMORPHISM Process by which a rock’s structure is

changed by heat, pressure, and moisture Two Basic Types:

Regional Local

REGIONAL METAMORPHISM Occurs in large areas Forms most of the metamorphic rock of

Earth’s crust Can occur during mountain-building

process

LOCAL METAMORPHISM Occurs in smaller, distinct areas Two Types:

Contact hot magma moves into rock, heating and changing it (can even change mineral compostion)

Deformational occurs at lower temperatures and is more due to pressure (composition does not change but deforms shape and texture)

CLASSIFICATION OF METAMORPHIC ROCKS

Based on a variety of properties: Parent rock Mineral content Texture Foliation—tendency to form bands of minerals or

split along parallel layers

CLASSIFICATION OF METAMORPHIC ROCKS

Metamorphic Rocks are also classified by their “grade” or degree of metamorphism:

Even the minerals in a

rock can change with

metamorphism (but not always!)

EXAMPLES OF METAMORPHIC ROCK

Quartzite a metamorphosed sandstone Marble a metamorphosed limestone Slate, phyllite, schist metamorphosed

shales Gneiss—most highly metamorphosed

from a variety of parent rocks

QUARTZITE

MARBLE

SLATE

SCHIST

GNEISS