The Rock Cycle three Main Families 

Igneous. Sedimentary & metamorphic rocks

Three families of rocks
The rock cycle consists of igneous rocks, sedimentary rocks and metamorphic rocks. These three families of rocks are constantly changing from one group into another. The rocks in each of these families are changing due to tectonic plate movement as crustal plates collide, move apart or slip past each other.

Pictures of igneous, sedimentary and metamorphic rocks

Metamorphic rock (left) Sedimentary rock (center) Igneous rock (right)

Igneous Rocks

Basalt
Andesite
Dacite
Rhyolite

Basalt

Andesite

Dacite

Rhyolite

There are four broad categories of igneous rocks.

Basalt is 45% to 54% quartz.
Andesite is 54% to 62% quartz.
Dacite is 62% to 69% quartz.
Rhyolite is 69% to 80% quartz.

Find out about these igneous rocks in the links below that form when a volcano erupts: pyroclastic rocksaa lavawelded tuffignimbritepyroclastic materialpahoehoe lava and basalt rocks

Where and how igneous rocks form

Igneous rocks 
Igneous rocks that form during violent volcanic eruptions are some of the most beautiful and deadliest natural events on Earth. All igneous rocks were once molten rock that formed during volcanic eruptions or cooled underground. The amount of quartz in the rock determines the type of igneous rock that forms.

Rock Cycle student book

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Sedimentary Rocks

Conglomerate
Petrified wood
Coquina

Conglomerate

Petrified wood

Coquina

Sedimentary rocks
Sedimentary rocks form when older rocks weather. The pieces of older rock are carried downstream to form clastic rocks which include shale, mudstone and siltstone.  Sedimentary rocks found in the rock cycle are varied and include three major groups: clastic rocks, organic rocks and chemical rocks. You will find more information on clastic rocks, organic rocks, limestone caverns, salt domes and coal formation in the links below.

Gneiss
Graphite schist
Marble
Serpentinite

Gneiss

Graphite schist

Pink marble

Serpentinite

Metamorphic rocks
Metamorphic rocks are the third group of rocks. Metamorphic rocks form when igneous, sedimentary and metamorphic rocks recrystallize without melting within the Earth. These rocks form intrusive rocks or plutonic rocks. Limestone rocks that crystallize into  metamorphic rocks form marble. Shale, a clastic rock, can recrystallize into gneiss a high-grade metamorphic rock.


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