Topic 3B – Rocks and the Rock Cycle

Ms Cooke

Earth Science

2015-2016

Rocks

Rocks are mixtures of minerals, organic material, glasses, and fragments of other rocks.

A single-mineral rock is both a rock and a mineral. It has the mineral’s definite composition and

properties. i.e. Rock Salt, Rock Gypsum, Dolostone

The Types of Rocks

Igneous – Mostly formed deep under the Earth’s surface, when magma cools and hardens. A small percent form from lava.

Sedimentary – Weathering and Erosion (the breakdown and transport of rocks) such as wind or water break down all rock types into fragments, called sediments. These sediments become compressed and cemented together forming sedimentary rocks.

Metamorphic – From forces such as heat and pressure, as well as chemical processes, that act on existing rocks, altering them to a new form.

The Rock Cycle

The Rock Cycle illustrates the changes the rock types undergo over time.

Some rocks have been through the cycle many times

We are recycling rocks!

The Rock Cycle – ESRT Pg 6

Rock Recycling

IGNEOUS ROCKS

Rocks formed by MELTING of existing rock to form a new rock

IGNEOUS ROCKS

IGNEOUS ROCKS come from molten rock (or magma)within the earth, or from lava (extruded from the surface).

The kind of Igneous Rock formed depends on what material was melted, and THE RATE of cooling.

Igneous rocks are classified based on their mineral composition and texture!

IGNEOUS ROCK TEXTUREIntrusive (Plutonic)

Form deep within the crust - magma Cool slooooooowly Have LARGE (visible)

crystals Coarse to Very Coarse

Grained 1mm to 10+ mm

Extrusive (Volcanic) Form at the surface –

lava Cool fast Have small to

microscopic crystals Fine Grained to Glassy

Less than 1 mm

IGNEOUS ROCK TEXTURE

Extrusive rocks may also be VESICULAR Have Gas Pockets Due to gases

escaping from the lava

If no gasses – Non-

Vesicular

Igneous Rock Mineral CompositionFelsic

Light Colored rocks Pink, White,

Clear

Feldspar and Quartz

Low Density

Mafic

Dark Colored rocks Blacks and

Greens

Iron (Fe) and Magnesium (Mg)

Amphibole, Pyroxene, Olivine

High Density

Intermediate

White, Grey, or Black Only

Grey or Salt and Pepper

Classifying Igneous Rocks ESRT Pg 6

Classifying Igneous Rocks ESRT Pg 6

Sedimentary Rocks

Rocks formed from compacting and cementing rock particles or fragments (sediments)

Sedimentary

Sedimentary Rocks form when rock fragments, organic materials, or minerals that have precipitated out of solution are compacted and cemented together.

Main Process of Formation

Converts loose sediment into sedimentary rocks

COMPACTION – Due to the layering by deposition the sediment is squeezed and the size of the pore space (air pockets) is reduced.

CEMENTATION – Sediments are “glued” together by the minerals that are deposited by water.

Main Process of Formation

Sedimentary Rock Types

Clastic Formed by the

deposition of sediments which are then compacted and cemented together.

Classified by Size of Sediments

Crystalline Formed by Minerals that

we once dissolved in water. Some form when minerals precipitate out of water.

Sedimentary Rock TypesClastic – Sediment Sizes

Particle Size

Boulder 25.6 cm and over

Cobbles 6.4 cm – 25.6 cm

Pebbles 0.2 cm – 6.4 cm

Sand 0.006 – 0.2 cm

Silt 0.0004 cm – 0.006 cm

Clay Less than 0.0004 cm

Sedimentary Rock TypesClastic – Sediment Sizes

Particle Size

Boulder 25.6 cm and over

Cobbles 6.4 cm – 25.6 cm

Pebbles 0.2 cm – 6.4 cm

Sand 0.006 – 0.2 cm

Silt 0.0004 cm – 0.006 cm

Clay Less than 0.0004 cm

Clastic – Conglomerate and Breccia

CONGLOMERATE – have larger sized rounded particles or fragments cemented by sand, silt, or clay.

BRECCIA – similar to conglomerates, but with angular particles.

Clastic – Sandstone

SANDSTONE – is composted of sang grains that have been cemented

Largely composed of quartz Many types are porous DOES NOT REACT WITH ACID

Clastic – Shale and Siltstone

SILTSTONE – consists of clay sized particles that are cemented and compacted

SHALE – consists of silt sized particles

Shale is VERY fine, usually dark colored (green, black, or red). Often splits into thin, flat pieces.

Siltstone is fine, but doesn’t split into flat sheets. Also called mudstone.

Clastic – Bioclastic – Organic Fragments

COAL Composed of mostly

CARBON Black

LIMESTONE Composed of mostly

Calcium Carbonate CaCO3

BUBBLES WITH ACID

Forms when living things are buriedbefore they can decay

Sedimentary Rock Types

Crystalline Formed by Minerals that

we once dissolved in water. Some form when minerals precipitate out of water.

Sedimentary Rock Types

Metamorphic Rocks

Changing a Rock’s Chemical Structure by Heat and Pressure

Changing the Chemical Structure Usually formed deep within the

Earth’s Crust Formed by Heat and Pressure

Causes rock’s chemical structure to change

Metamorphic TypesREGIONAL The process by which

heat and pressure deep under the surface change a LARGE area of rock

Mountain Building

CONTACT Process in which rocks

come in contact with magma, causing changes to occur

Small area around magma intrusion

Grades of Metamorphism Low Grade – Low temperature and

pressure (just enough to change). Slate and Phyllite – Small crystals, fine

grained Intermediate – Higher temperature and

pressure than low grade Schist – larger mica crystals

High Grade – Highest Temperature and pressure possible without melting Gneiss – Crystal alignment into bands

Grades of Metamorphism

Foliation and Banding Foliated Rocks – When metamorphism

results in the alignment of crystals into layers. Schist

Banding – When crystals grow in alternating light and dark layers Gneiss

Non-foliated – No alignment of crystals or layering. Marble

Foliation and Banding

Foliation and Banding

Foliation and Banding