What is a Rock? Naturally-occurring mixtures of minerals, mineraloids, glass or organic matter.

What is a Rock? Naturally-occurring mixtures of minerals, mineraloids, glass or organic matter.

What is a Rock? Rocks are divided into 3 groups based on how they were formed: IGNEOUS SEDIMENTARY METAMORPHIC

What is the difference between a rock and a mineral? Rocks are made up of ONE or MORE minerals.

Made of elements Must be inorganic Solid Can be made from organic materials Made only of compounds Can be made of lava/ magma Mixtures made of minerals Naturally occurring Have crystals Can be man made Can be formed from solutions

Once a rock is formed, does it stay the same rock forever? NO!

Rocks are continually changed by many processes, such as weathering, erosion, compaction, cementation, melting, and cooling Rocks can change to and from the three types

What is the process through which rocks change? The Rock Cycle earth materials change back and forth among the different types of rocks

No set path a rock takes to become another kind of rock

IGNEOUS Weathering, Erosion, Compaction, Cementation Melting, Solidification Melting, Solidification Recrystallization Recrystallization SEDIMENTARY METAMORPHIC Weathering, Erosion, Compaction, Cementation

How are rocks redistributed? The core, mantle, & crust are one giant rock recycling machine

Classifying Rocks When classifying a rock sample geologists observe the rock s color and texture and determine its mineral composition. Texture: the size, shape, and pattern of the rock s grain. Color: the apparent color of the rock, on the inside and the outside. Mineral composition: The minerals that make up the different parts of a rock.

Ignis = Latin for fire Formed from the cooling of either magma or lava The most abundant type of rock Classified according to their origin and composition

ORIGIN Where rocks are formed Below ground = from magma (intrusive igneous rock) Usually have LARGE crystal grains (they cooled slowly)

Some have large & small crystals (called porphyritic)

Above ground = from lava (extrusive igneous rock) Usually have SMALL or NO crystals (they cooled too quickly)

Peridotite: Intrusive or Extrusive? Why?

Granite: Intrusive or Extrusive? Why?

Porphyry: Intrusive or Extrusive? Why?

Obsidian: Intrusive or Extrusive? Why?

COMPOSITION What kind of substances the rocks are made of

Basaltic Igneous Rocks made from lava/magma that is low in silica, rich in iron and magnesium. Rocks are dark-colored.

Granitic Igneous Rocks made from magma/lava high in silica and oxygen. Rocks are lightcolored.

Andesitic Igneous Rocks have a composition between basaltic and granitic.

Diorite

Basalt

Granite

Subduction A rock that gets caught up in the subduction zone may get dragged down with the oceanic plate. As the rock gets dragged down, they undergo metamorphism. Some parts of the rocks get taken all the way down to the mantle where they slowly mix with the rest of the mantle. this is the only way that rocks formed on the continent get recycled with the mantle.

Formed from sediments (rock fragments, mineral grains, animal & plant remains) that are pressed or cemented together or when sediments precipitate out of a solution.

These sediments are moved by wind, water, ice or gravity. Sedimentary rocks represent 7% of the Earth s crust, but they cover 70% of the Earth s surface. Sedimentary rocks are fossil-carrying rocks.

What turns sediments into solid rock? Water or wind breaks down and deposits sediment (erosion & deposition)

Lithification The process by which sediment becomes sedimentary rock 1 st step : erosion 2 nd step : deposition 3 rd step : compaction 4 th step : cementation

Erosion Erosion is the wearing away of exposed surfaces by agents such as wind, moving water and ice. These agents usually contain weathered rock debris. Rock fall under gravity is also erosion. * Weathering breaks down while erosion carries and moves to another place.

Weathering The process in which rocks are broken down by chemical and/or physical mechanisms into smaller particles. There are three types of weathering Physical weathering: physical action which breaks up rocks. An example of this is freezethaw weathering Chemical Weathering: when the rock is attacked by chemicals. An example of this is how acid rain breaks down limestone. Biological weathering: occurs when rocks are weakened and broken down by animals and plants. A tree root system that is slowly splitting rocks is an example of this type of weathering..

Compaction The result of this pressure is a compaction of the sediment it is squeezed together causing a reduction in pore space and a sticking together of the grains. Under pressure, some chemical sediments, like halite, may recrystallize into a solid state.

Most sediments are deposited in water containing dissolved minerals. The water flows through the sediment and some of these minerals precipitate on the grain surfaces. With time, this material glues the sediment together into a solid- a sedimentary rock. Cementation

Transportation This process occurs when the particles created by weathering are carried by ice, air, or water to a region of lower energy known as a sedimentary basin.

The heavy sediments press down on the layers beneath (compaction)

Dissolved minerals flow between the particles and cement them together (cementation)

How can sedimentary layers help us understand the age of fossils? As sedimentary rocks are deposited, they form horizontal layers Scientists know that the layers on top (and the fossils in the top layer) are YOUNGER than the fossils in lower layers.

3 Types of Sedimentary Rocks: Clastic (also called Detrial) made of broken pieces of other rocks

3 Types of Sedimentary Rocks: Organic remains of plants and animals are deposited in thick layers Examples Fossil rich limestone is made from the shells of ocean animals; used to make chalk

3 Types of Sedimentary Rocks: Chemical minerals dissolved in lakes, seas, or underground water Mineral crystals are made as the shallow water that has flooded the bottom of Death Valley evaporates. Click on image for full size (66K JPG) Courtesy of Martin Miller, University of Oregon

Examples Limestone made when calcite mineral precipitates from sea water Rock Salt made from evaporation of sea waters

Rocks that have changed due to intense temperature and pressure Meta means change and morphosis means form in Greek Igneous, sedimentary and other metamorphic rocks can change to become metamorphic rocks

What occurs in the Earth to change these rocks? Pressure from overlying rock layers High heat, but not enough to melt the rock Rocks may be flattened or bent or atoms may be exchanged to form new minerals.

*You can think of metamorphic rocks as a squished peanut butter & jelly sandwich in your lunch.

How are metamorphic rocks classified? Foliated mineral grains are flattened and line up in parallel bands Example: gneiss formed from rearrangement of minerals in granite into bands

How are metamorphic rocks classified? Non-Foliated No bands are formed Example: marble formed from limestone

Where do metamorphic rocks usually form? Where magma intrudes relatively cool rock Near colliding plates (near mountain ranges) Places that are covered miles thick with other rock causing pressure When hot water intrudes rock Where a meteorite strikes Earth (rare) Where lightning bolts strike rocks (rare)