Physical Science Notes

Rocks: Materials of the Lithosphere

Rocks: aggregates of minerals.

Three types of rocks: Igneous, Sedimentary and Metamorphic

Rock Cycle: a description of the processes whereby rocks change from one type to another.

Terms

lava
molten rock that pours out of volcanic vents onto the Earth's surface
magma
a liquid that exists beneath the surface of the Earth's melted rock
sediment
small grains of rock formed by weathering processes
lithification
the process of turning to stone

Igneous Rock

Two main classifications: Intrusive (plutonic) and extrusive (volcanic).

Igneous rocks form from the crystallization or solidification of magma or lava.

Plutonic igneous rocks form from the slow cooling of magma and develop large crystals and a coarse-grained texture.

Volcanic igneous rocks form from the rapid cooling of lava and have a fine-grained texture, a glassy texture (quenching), or a frothy texture. Crystals do not have enough time to grow and develop.

Igneous rocks are classified on the bases of texture and mineral composition.

Textures include: coarse-grained, fine-grained, glassy, frothy and porphyritic (mixed) texture.

Igneous Rock Classification
TypesCoarseFine
UltramaficPeridotiteKolmatite
BasalticGabbroBasalt*
AndesiticDioriteAndesite
GraniticGranite*Rhyolite

*Most common types

 
rock cartoon

Weathering of Rocks to Form Sediment

Weathering:

Mechanical: physical breaking up of rocks.
Chemical: changes in chemical composition

Mechanical Weathering

Breaking into smaller pieces increases surface area. More surface exposed increases the rate of chemical weathering.

Types of Mechanical Weathering

Chemical Weathering

Water contains dissolved oxygen and carbon dioxide. Some important chemical reactions are:
reaction with oxygen to form oxides
reaction with weak acids to dissolve minerals into solution

Feldspar weathers to form clay and quartz weathers to form sand.

Sedimentary Rocks

Sedimentary rocks are formed from compacted and cemented sediment. There are two main types: chemical and detrital. The sediment is formed from weathering and erosion. Agents of erosion include running water, winds, waves and glacial ice.

Lithification: compaction and cementation

Sedimentary Rocks account for 5% by volume of Earth's outer 10 miles but 75% of rock outcrops are sedimentary.

Sedimentary rocks hold clues to the Earth's past

Coal is a valuable sedimentary rock (and is not composed of minerals)

Classifying Sedimentary Rocks

Detrital
Conglomerate/Breccia
Sandstone
Shale (Siltstone and Claystone)
Chemical
Limestone
Coquina
Chalk
Evaporites
Halite
Gypsum
Coal
Lignite
Bituminous

Sedimentary rocks typically produce beds or strata

Metamorphic Rock

Meta (Greek): change
Morph (Greek): shape or form

Rocks that are formed from other rocks through processes of applied pressure and heat or chemical reactions causing changes in appearance. Pressure and temperature increase with depth below the Earth's surface.

Foliated texture: minerals become aligned resulting in a banded appearance.

Examples of Metamorphic Rock