Rocks Review
Rocks – a mixture of minerals and other materials. These minerals are known as rockforming minerals.
Geologists identify rocks by color, texture and mineral composition to classify a rock.
Color – can tell how the rock was formed (doesn’t provide enough information to
identify the rock.
Texture – how the rocks was formed (glassy and smooth – rough)
Mineral Composition – geologist study the shape and color of crystals to identify
minerals.
Texture Identification
 Grain Pattern: Banded vs. Non-Banded
 Grain Size: Fine Grain vs. Large Grain
 Grain Shape: Rounded Grain vs. Jagged Grain
Rock Types
Sedimentary Rocks – Formed by a process of Weathering, Erosion, Deposition,
Compaction, and Cementation (WEDCC)





Weathering – breaking down of rock by wind and water
Erosion – running water, wind, and loose ice carry away fragments of rocks
Deposition – dropping off of sediments (coming to a rest)
Compaction – process where sediments are pressed together
Cementation – process which minerals crystalized and glued sediments together
Contains fossils
As sedimentary rocks are deposited, they form horizontal layers – the layers on top
are younger than the layers below them
Metamorphic Rocks – rocks that have changed die to intense temperature and
pressure
What



occurs that change these rocks
Pressure from overlaying rock layers (pressure from the rocks above)
High heat, but not enough to melt the rock
Rocks may be flattened or bent or atoms may be exchanged to form new
minerals
How metamorphic rocks are classified
 Foliated – mineral grains are flattened and line up in parallel bands
 Non-Foliated – no bands are formed
Where metamorphic rocks usually form
 Where magma intrudes relatively cool rock
 Near colliding boundaries (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)
Igneous Rock – formed from the cooling of either magma (below earth) or lava (above
the earth)
Intrusive Rock – inside the earth – magma - usually have large crystals-cooled slowly
due to heat within the earth
Extrusive Rock – above the earth – lava (volcanoes) – small or no crystals – cooled
quickly due to lava reaching the cool air

The most abundant type of rock
What is the process through which rocks change?
The Rock Cycle is a series of processes on Earth’s surface and in the crust and mantle
that slowly change rocks from one kind to another. (Takes thousands of years to go
through the process)
Once a rock is formed it does NOT stay the same rock forever – Rocks are continually
changing (WEDCC – Heat and Pressure – Melting and Cooling)