There are 3 types of rocks found on Earth:

IgneousSedimentaryMetamorphic

Igneous Rocks are formed by melting, cooling, and crystallization of other rocks.

Igneous rocks form as a result of volcanic activity, hot spots, and melting that occurs in the mantle.

Igneous rocks are common along plate boundaries or mantle hot spots

Igneous rocks are classified using their texture in the following ways:GlassyAphanitic (no visible

crystals)Phaneritic (visible crystals)Porphyritic (Some visible

and some not visible crystals)

Crystal size is used to classify igneous rocks.

Crystals form as the rock cools, and the crystal size can tell us a lot about its cooling history:The larger the crystals,

the slower it cooled.

Glassy igneous rocks have no crystal structure, and probably formed by very rapid cooling (such as on the surface of a lava, or when a lava enters the water.)

Aphanitic rocks have no visible crystals, and probably formed by fast cooling above ground.

Phaneritic rocks have visible crystals, and probably formed by slow cooling below ground.

Porphyritic rocks have both visible and nonvisible crystals, and probably formed by two different cooling events.

Dark igneous rocks are formed from basaltic or mafic magma. (Mafic because it contains a lot of magnesium and iron).

The magma that forms these rocks is usually very hot (around 1000°C) and viscous (about the same viscosity as ketchup.)

Light colored igneous rocks are formed from silicic (high silica content) or felsic magmas.

The magmas that form these rocks is usually more cool, (lower than 850°C), and more viscous (about the viscosity of peanut butter.)

Structures and formations seen in igneous rocks include: Hexagonal columnar

jointsPahoehoe lava flowsDikes, sills, and

batholiths (plutons)Pillow basaltsVolcanoes

The most common types of igneous rocks include:RhyoliteAndesiteBasaltGraniteDioriteGabbro

Sedimentary rocks are formed by weathering, erosion, deposition, compaction, and cementation of other rocks.

Sedimentary rocks form in areas where water, wind, or gravity deposit sediments.

Sedimentary rocks are likely to form in areas such as:DeltasBeachesRiversGlaciersSand dunesShallow seasDeep oceans

Sedimentary rocks are classified into two groups:

Clastic rocksChemically formed rocks

Sedimentary rocks are Clastic if they are made of pieces of other rocks that have been weathered and eroded.

Clastic rocks are grouped based on the size of grain that they are made from.

Very small particles make up mudrock.

Medium sized particles make up sandstone.

Large particles make up conglomerates.

Sedimentary rocks that form from chemical processes are called biochemical rocks (formed from living things) or Chemical precipitates (formed from lakes or shallow seas.)

Structures and formations seen in sedimentary rocks include:StratificationCross beddingGraded beddingRipple marksMud cracksFossils

ConglomerateSandstoneShaleLimestoneGypsumOolitesChert (including

black flint and red jasper)

Metamorphic rocks are formed by heat and pressure changing one type of rock into another type of rock.

Metamorphic rocks form near lava intrusions, at plate subduction zones, and in deep mountain roots.

Lava intrusions can provide heat that causes metamorphic rocks to form. These small areas of metamorphic rock form from contact metamorphosis.

Rocks that metamorphose because of increasing heat and pressure found at plate subduction zones and in deep mountain roots form large areas of metamorphic rock through regional metamorphosis.

Metamorphic rocks are classified into 2 major groups:FoliatedNonfoliated

Foliated rocks form when differential pressure causes minerals to form in layers.

These rocks will have stripes or planes that they will break easily along.

These “stripes” don’t usually line up with the original bedding planes in sedimentary rocks.

Nonfoliated metamorphic rocks formed in areas where the pressure from all sides was equal, so there is no “linear” quality to the rocks.

Structures and formations seen in metamorphic rocks include:FoldingPlastic deformationStretchingAlternating dark and light

layers (gneissic foliation)

Some common types of metamorphic rock include:SlateSchistGneissAmphiboliteMarbleQuartziteMetaconglomerate