Types of rocks

 Intrusive Rocks: igneous rocks that formed when magma hardened beneath the earth’s surface..  Rapid cooling lava forms fine-grained igneous rocks with small crystals..  Slow cooling

Three Types of Rocks

 How are igneous rocks classified?

 Igneous rocks (ig nee us) are formed from magma or lava Igneous means fire-formed.

 Igneous rocks are classified according to

their origin, texture, and mineral

composition

 The origin of a rock is where the rock was formed.

 Extrusive Rocks: igneous rocks which formed

from lava which erupted on the earth’s surface.

 Ex Basalt: forms most of the crust which

includes the crust on the ocean floor.

 Intrusive Rocks: igneous rocks that formed when magma hardened beneath the earth’s surface

 Ex Granite: the most abundant intrusive rock in the part of the crust that makes up the

continents Granite forms the core of many

mountain ranges

 Texture

 The texture of an igneous rock depends on the size and shape of its mineral crystals.

 The texture may be fine grained,

coarse-grained, glassy, or porphyritic.

 Rapid cooling lava forms fine-grained igneous rocks with small crystals

 Slow cooling magma forms coarse-grained rock with large crystals.

 A rock with large crystals scattered on a

background of much smaller crystals has a

porphyritic texture (pawr fuh rit ik).

 Porphyritic rocks form when intrusive rocks cool

in two stages As the magma begins to cool,

large crystals form slowly The remaining

magma, however, cools more quickly, forming

small crystals.

 Extrusive rocks have a fine grained or glassy

texture.

 Mineral Composition

 Most of Earth's minerals contain silica, a

material formed from oxygen and silicon.

 The silica content of magma and lava affects the types of rock they form

 Lava that is low in silica usually forms

dark-colored rocks such as basalt

 Magma that is high in silica usually forms colored rocks, such as granite.

Observing

You can learn about a rock's mineral

composition by looking at a thin slice.

1 The diagram shows a thin slice of an

igneous rock The key identifies

different minerals Which mineral makes

up most of this rock? How did you

decide?

2 Which mineral is present in the

smallest amount?

 From Sediment to Rock

 Sedimentary rocks form from particles

deposited by water and wind These particles are called sediment.

 Sediment are small, solid pieces of material that come from rocks or living things.

 Erosion occurs when running water or wind

loosen and carry away these fragments of

rock.

 The moving water or wind slows and deposits the sediment.

 After sediment has been deposited, the

processes of compaction and cementation

change the sediment into sedimentary rock.

 Sediment may include shells, bones, leaves, stems, and other remains of living things.

 Over time, any remains of living things in the sediment may slowly harden and change into fossils trapped in the rock.

Sedimentary Rock Formation Sedimentary rocks form through the deposition,

compaction, and cementation of sediments A Water or wind deposits sediment

B The heavy sediments press down on the layers beneath C Dissolved minerals

flow between the particles and cement them together.

 At first the sediments fit together loosely But

gradually, over millions of years, thick layers of

sediment build up These layers are heavy and press

down on the layers beneath them Then compaction

occurs Compaction is the process that presses

sediments together.

 While compaction is taking place, the minerals in the

rock slowly dissolve in the water The dissolved minerals seep into the spaces between particles of sediment

Cementation is the process in which dissolved minerals crystallize and glue particles of sediment together.

 There are three major groups of sedimentary rocks: clastic rocks, organic rocks, and

chemical rocks.

 Clastic Rocks

 Clastic rocks form when rock fragments are

squeezed together.

 Ex shale, sandstone, conglomerate and breccia

 Usually occurs under water.

 Shale forms from tiny particles of clay.

 Sandstone forms from the sand on beaches, on the ocean floor, in riverbeds, and in sand dunes

Sandstone is a clastic rock formed from the

compaction and cementation of small particles of sand.

 Some sedimentary rocks contain a mixture of rock

fragments of different sizes The fragments can

range in size from sand and pebbles to boulders If the fragments have rounded edges, they form a

clastic rock called conglomerate A rock made up of large fragments with sharp edges is called breccia

(brech ee uh).

Sandstone Shale

Breccia

Coal forms from the remains of swamp plants buried in

water As layer upon layer of plant

remains build up, the weight of the layers squeezes the

decaying plants

Over millions of years, they slowly change into coal.

Coal

How does limestone form? In the ocean, many living things, including coral, clams, oysters, and snails, have shells or

skeletons made of calcite When these animals die, their shells pile up as sediment on the ocean floor.

Slowly, the pressure of overlying layers compacts the sediment Some of the shells dissolve, forming a solution of calcite that seeps into the spaces between the shell fragments Later, the dissolved material comes out

of solution, forming calcite The calcite cements the shell particles together, forming limestone.

mineral halite, which forms by evaporation.

Examples of chemical rocks

Gypsum

 The word metamorphic comes from the Greek words meta , meaning “change,” and morphosis,

meaning “form.”

 Heat and pressure deep beneath Earth's

surface can change any rock into metamorphic rock

 When rock changes into metamorphic rock, its appearance, texture, crystal structure, and

mineral content change.

 While metamorphic rocks are forming, high temperatures change the size and shape of the grains, or mineral crystals, in the rock

 In addition, tremendous pressure squeezes rock so tightly that the mineral grains may line up in flat, parallel layers

 Geologists classify metamorphic rocks by the arrangement of the grains that make up the rocks

Metamorphic Rocks Great heat and pressure

can change one type of rock into another

Granite becomes gneiss, shale becomes slate, and sandstone changes to quartzite.

 Metamorphic rocks that have their grains

arranged in parallel layers or bands are said to

be foliated Ex Slate, schist, gneiss

Slate Gneiss

Schist

 Sometimes metamorphic rocks are

nonfoliated The mineral grains in these

rocks are arranged randomly Metamorphic rocks that are nonfoliated do not split into layers.

 Igneous rocks form from magma or lava.

texture, and composition.

compacted and cemented together.

rocks, organic rocks, and chemical rocks.

surface, heat and pressure can change any type of

rock into metamorphic rock.

whether the rock is foliated or nonfoliated.