Rocks

What is a Rock?

• It is a hard substance that is made of one or more minerals

Major Rock Groups• Rocks are classified according to how

they are formed.

1. Igneous Rocks –

“fire formed”

2. Sedimentary Rocks - “sediment rocks”

3. Metamorphic Rocks - “changed rock”

Rock Cycle

• The natural process of one rock type changing into another rock type.

Magma

IgneousRock

SedimentSedimentary

Rock

MetamorphicRock

Heat, Pressure,& Chemical Reactions

Melting

Cooling & Crystallizing

Erosion & Weathering

Cementing & Compacting

Igneous Rocks

• Rocks that are formed from magma (below) or lava (above)

• Make up a large portion of the crust.

Igneous Classification

• Based on composition and texture.

1. Texture

• the size, shape, & relationships of the mineral crystals in a rock

a. Coarse Grain - large crystals

GraniteDiorite

b. Fine Grain - small crystals

c. Vesicular - full of holes because of gas bubbles

PumiceBasalt

RhyoliteBasalt

d. Glassy - cools too fast to form crystals

e. Pyroclastic - cemented volcanic ash, cinders, & bombs

Obsidian

Scoria

Pumice

2. Composition

• Magma will cool and form mineral crystals at different temperatures.

• Geologists can identify igneous rocks based on the specific minerals in the rock.

Igneous rocks with Igneous rocks with finefine grain texture are made grain texture are made from lavafrom lava(Extrusive).(Extrusive).

Igneous rocks with Igneous rocks with coarsecoarse grain texture are grain texture are made from magma made from magma (Intrusive).(Intrusive).

Types of Igneous Rocks

• Basaltic-Dark-colored, dense. Formed from magma rich in iron and magnesium low in silica.

• Granitic- Light-colored, low density. Formed from magma with high silica.

• Andesitic- Between Granitic and Basaltic

• Frothy-Glassy with holes.

Sedimentary Rocks

• Rocks formed by the cementing & compacting of small rock particles.

How Are They Formed?

1. As rocks are broken down by water & wind(weathering/erosion,) the rock particles (sediment) will sink to the bottom of a water source.

Sedimentary is formed in three main ways—

• by the deposition of the weathered remains of other rocks

• by the deposition of the results of biogenic activity;

• by precipitation from solution.

2. Over a long period of time the sediment will build up in layers. The upper layers cause pressure on the lower layers (compacting.)

------physical process

Pressure =compacting

3. In other cases, chemicals within the sediment will “glue” the sediment together forming a rock

(cementing.)

-----chemical process

Sedimentary Classification

• Grouped based on how the rock was formed & where the sediment came from.

1. Clastic Rock (physical)

• Sedimentary rocks that are made of previously existing rock fragments.

• These rocks are named based on the size & shape of the rock fragments within the main rock.

EX: Sandstone & Shale

Conglomerate

Breccia

Sandstones

Shales

2. Non-clastic Rock (chemical)

• Includes rocks that were formed as a result of mineral crystallization when water evaporated.

Ex: rock salt

• Includes organic rocks such as coal & fossils

• Includes cavernous rocks such as stalactites & stalagmites.

• Includes microcrystaline quartz rocks

EX: Limestone & Flint

Flint/Chert

Limestones

Metamorphic RocksMetamorphic rocks are rocks

that have "morphed" into another kind of rock.

These rocks were once igneous or sedimentary rocks.

The rocks are under tons and tons of pressure, which fosters heat build up, and this causes them to change.