Unit 2Chapter 6

Rocks

Section 1 Rocks and the Rock Cycle

Three Major Types of Rocks 1. Igneous - Formed from the cooling and hardening

(solidifying) of magma and lava from within the earth.2. Sedimentary - Formed by the hardening of layers

of sedimentTypes of sediments1. rock fragments2. plant and animal remains3. chemicals (water)

3. Metamorphic - Rocks that are changed into new kinds of rocks

http://geology.com/rocks/

Rock Cycle

This means that any rock can become either:• Igneous• Sedimentary• Metamorphic

depending on how it is influenced by the environment.

Properties of Rocks

Bowens Reaction

Canadian geologist in 1928 proposed a hypothesis on the formation of minerals.

As the magma cools different minerals can form.

Chemical Stability of Minerals

Physical Stability of Rocks

Section 2 Igneous Rocks

Formation of Magma

Magma

Melted rock under the surface

Lava

Melted rock on top of surface

Textures of Igneous Rocks

1. Extrusive - formed outside the earth's crust from lava.

Extrusive exited from the earth

2. Intrusive - formed within the crust from the magma.

Intrusive inside the earth

TEXTURE - depends on the size of the rock crystals. The rate of cooling determines crystal size.

a. Intrusiveslow cooling - large mineral grains

(plutonic after the Roman God of the underground Pluto)ex. granite - course grained

b. Extrusive cools faster - small mineral grains (volcanic)

ex. basalt - fine grainedc. intermediate cools

no crystals form, smooth as glassex. Obsidian

VesicularGas pockets form in rock when the magma cools quickly

PORPHYRY - (Por Fi Ree) - rocks with two texturesa. One mineral solidifies - forms large crystalsb. The other mineral solidifies later - there is less room - therefore the crystals are smaller.

Intrusive Igneous Rocks

Batholiths and Stocks

BatholithsLarge igneous intrusions at least 100kms.Forms mountain bases like Sierra Nevada in Cal.

StockSmaller than 100kms

LaccolithsWhen magma pushed up between rock layers, if forms a domeBlack Hill of South Dakota

Sills and DikesSills are parallel layers, small area between layersDikes cut across rock layers

Extrusive Igneous Rocks

When lava hardens on the surface into a rock .

Composition of Igneous Rocks

Felsic High silica acid type of magma. NOT much Ca, Fe or Mg only light colored Si.Mostly intrusive magma - slow thick - does not reach the surface easily.Forms granite, quartz, orthoclase feldspar.

Mafic Low Si concentrationsHigh in Ca, Fe and MgMuch hotter - easier to flow to the surface, extrusiveForms basalt and gabbro

IntermediateMade up of mostly plagioclase feldspar, hornblende, pyroxene, and biotite mica. Diorite and andesite

Section 3 Sedimentary RocksFormation of Sedimentary Rocks

CompactionWhen sediments get squeezed down, the pore space is reduced.

CementationWhen sediments become glued together with another mineralThese cements enter the pore spaces between sediments. They glue them together to make a clastic sediment rock

Types of cement:1. Silica - from weathered quartz - grey or white2. Lime - from weathered calcite - grey or white3. Iron - from weathered Fe containing rock - red or brown4. Pressure can act as a cement in clay and silt.

Chemical Sedimentary Rock

Forming Chemically Derived Sedimentary Rocks

Minerals must leave water and form a layer on the bottom either by evaporation or chemical actions

Limestone - tiny grains of calcite deposited in the seas or lakes. Grey or tan in color. Smooth and dense.

Rock Salt - table salt - made of mineral Halite. Forms when salt water dries up, the salt is left behind. Found in thick layers around the world.

Gypsum Found in layers around the world. Formed from mineral gypsum

Organic Formed from remains of once living organisms (plants and animals)Coal- plant remains, Fossil Limestone and Chert

Clastic Sedimentary rocksFragments must come from pre-existing rocks

Fragments come from weathering and erosionagents: water - rain, rivers, wind, glaciers

Fragment sizes -boulders, cobbles, pebbles, gravels, sand, silt and clay

Fragments need to be cemented together to make rocks.

Conglomerate - very course mixture of rounded pebbles and sand of various different sediment types (breccia is angular fragments).

Sand Stone - grains of quartz cemented together. Very porous with a lot of small holes or openings. Permeable, able to absorb water.

Shale - tiny flakes of kaolin (clay). Held together by pressure, not cement. Very tiny

holes, cannot absorb water. Smooth and easily broken.

Characteristics of Clastic SedimentsThe characteristics of the sediments are determined by the way they are transported and deposited.

4 ways sediments are transportedWater, Ice, Wind, Gravity

SortingRiver Deposits - A river's motion causes it to carry sediment. When the river slows it cannot carry its

sediments. Sediments fall to the bottom

https://www.classzone.com/books/earth_science/terc/content/visualizations/es0604/es0604page01.cfm?chapter_no=visualization

AngularityNot rounded sediments. Broken and sharper edges

Sedimentary Rock Features1. Stratification -visible layers (beds) within rocks or rock structures. This layering is caused by changes in the

rock materials.ex. a layer of Sand a layer of Clay a layer of Silt

2. Cross-beds and Graded BedsCross bedding - bedding layers formed near or on sand dunes or river delta's - not flat but slantedGraded Beds - different types of materials deposited within a layer

3. Ripple MarksCaused when wind or water left a mark on the sandy surface and hardened.

4. Mud CracksOccur when clay and silt dry, they contract and spaces form. These spaces can get buried and become rock.

5. Fossils and ConcretionsFossils

Are remains, impressions or other evidence of existing plants and animals preserved in rocks.*Only Found in Sedimentary Rocks!!!!

Animal dies - bone does not decay, it gets buried. Rock eventually decays but a hole is left. The hole fills in with minerals, the minerals harden, a fossil is formed.

Concretion - nodules or "lumps" of fine grained silica.Chert - name of silicaFlint - dark grey or black chert

Geode - Limestone with hollow spheres that are lined with quartz or calcite crystals.Limestone middle dissolves in water, then the water

deposits quartz or calcite.

Section 4 METAMORPHIC ROCKS -

Are made from existing rocks by the action of:

1. heat - NO MELTING

2. pressure

3. chemical action

Formation of Metamorphic Rock

Contact MetamorphismWhen hot magma moves into rocks, heating and changing occurs in a small area. The Rock Does Not Melt!

A chemical change occurs by rearranging the minerals forming a new rock.

Regional or Dynamic metamorphismThis is the major source of metamorphic rock. It occurs in large areas, often associated with mountain building.

Classification of Metamorphic Rock

Properties of metamorphic rock depend on the parent rock or the minerals in the original rock. The parent rock’s characteristics and traits can be seen in certain metamorphic rocks.

Foliated Rocksmineral are arranged in planes or bandsHeat and pressure causes them to re-align in bandsInclude

Slate, Schist, Gneiss

Nonfoliated RocksThey do not have visible bands. Looks distorted or deformedDistortion or deformation:

1. Low temperatures and high pressure2. The sedimentary rock gets laid down in horizontal layers3. They get buried deep within the earth and are subjected to low heat and pressure; like where

there is a fault line.4.The grains of rock get squeezed together and the heat re-arranges minerals –

a new different rock is formed.

Quartzite , Marble