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Topic 3B – Rocks and the Rock Cycle
Ms Cooke
Earth Science
2015-2016
Rocks
Rocks are mixtures of minerals, organic material, glasses, and fragments of other rocks.
A single-mineral rock is both a rock and a mineral. It has the mineral’s definite composition and
properties. i.e. Rock Salt, Rock Gypsum, Dolostone
The Types of Rocks
Igneous – Mostly formed deep under the Earth’s surface, when magma cools and hardens. A small percent form from lava.
Sedimentary – Weathering and Erosion (the breakdown and transport of rocks) such as wind or water break down all rock types into fragments, called sediments. These sediments become compressed and cemented together forming sedimentary rocks.
Metamorphic – From forces such as heat and pressure, as well as chemical processes, that act on existing rocks, altering them to a new form.
The Rock Cycle
The Rock Cycle illustrates the changes the rock types undergo over time.
Some rocks have been through the cycle many times
We are recycling rocks!
The Rock Cycle – ESRT Pg 6
Rock Recycling
IGNEOUS ROCKS
Rocks formed by MELTING of existing rock to form a new rock
IGNEOUS ROCKS
IGNEOUS ROCKS come from molten rock (or magma)within the earth, or from lava (extruded from the surface).
The kind of Igneous Rock formed depends on what material was melted, and THE RATE of cooling.
Igneous rocks are classified based on their mineral composition and texture!
IGNEOUS ROCK TEXTUREIntrusive (Plutonic)
Form deep within the crust - magma Cool slooooooowly Have LARGE (visible)
crystals Coarse to Very Coarse
Grained 1mm to 10+ mm
Extrusive (Volcanic) Form at the surface –
lava Cool fast Have small to
microscopic crystals Fine Grained to Glassy
Less than 1 mm
IGNEOUS ROCK TEXTURE
Extrusive rocks may also be VESICULAR Have Gas Pockets Due to gases
escaping from the lava
If no gasses – Non-
Vesicular
Igneous Rock Mineral CompositionFelsic
Light Colored rocks Pink, White,
Clear
Feldspar and Quartz
Low Density
Mafic
Dark Colored rocks Blacks and
Greens
Iron (Fe) and Magnesium (Mg)
Amphibole, Pyroxene, Olivine
High Density
Intermediate
White, Grey, or Black Only
Grey or Salt and Pepper
Classifying Igneous Rocks ESRT Pg 6
Classifying Igneous Rocks ESRT Pg 6
Sedimentary Rocks
Rocks formed from compacting and cementing rock particles or fragments (sediments)
Sedimentary
Sedimentary Rocks form when rock fragments, organic materials, or minerals that have precipitated out of solution are compacted and cemented together.
Main Process of Formation
Converts loose sediment into sedimentary rocks
COMPACTION – Due to the layering by deposition the sediment is squeezed and the size of the pore space (air pockets) is reduced.
CEMENTATION – Sediments are “glued” together by the minerals that are deposited by water.
Main Process of Formation
Sedimentary Rock Types
Clastic Formed by the
deposition of sediments which are then compacted and cemented together.
Classified by Size of Sediments
Crystalline Formed by Minerals that
we once dissolved in water. Some form when minerals precipitate out of water.
Sedimentary Rock TypesClastic – Sediment Sizes
Particle Size
Boulder 25.6 cm and over
Cobbles 6.4 cm – 25.6 cm
Pebbles 0.2 cm – 6.4 cm
Sand 0.006 – 0.2 cm
Silt 0.0004 cm – 0.006 cm
Clay Less than 0.0004 cm
Sedimentary Rock TypesClastic – Sediment Sizes
Particle Size
Boulder 25.6 cm and over
Cobbles 6.4 cm – 25.6 cm
Pebbles 0.2 cm – 6.4 cm
Sand 0.006 – 0.2 cm
Silt 0.0004 cm – 0.006 cm
Clay Less than 0.0004 cm
Clastic – Conglomerate and Breccia
CONGLOMERATE – have larger sized rounded particles or fragments cemented by sand, silt, or clay.
BRECCIA – similar to conglomerates, but with angular particles.
Clastic – Sandstone
SANDSTONE – is composted of sang grains that have been cemented
Largely composed of quartz Many types are porous DOES NOT REACT WITH ACID
Clastic – Shale and Siltstone
SILTSTONE – consists of clay sized particles that are cemented and compacted
SHALE – consists of silt sized particles
Shale is VERY fine, usually dark colored (green, black, or red). Often splits into thin, flat pieces.
Siltstone is fine, but doesn’t split into flat sheets. Also called mudstone.
Clastic – Bioclastic – Organic Fragments
COAL Composed of mostly
CARBON Black
LIMESTONE Composed of mostly
Calcium Carbonate CaCO3
BUBBLES WITH ACID
Forms when living things are buriedbefore they can decay
Sedimentary Rock Types
Crystalline Formed by Minerals that
we once dissolved in water. Some form when minerals precipitate out of water.
Sedimentary Rock Types
Metamorphic Rocks
Changing a Rock’s Chemical Structure by Heat and Pressure
Changing the Chemical Structure Usually formed deep within the
Earth’s Crust Formed by Heat and Pressure
Causes rock’s chemical structure to change
Metamorphic TypesREGIONAL The process by which
heat and pressure deep under the surface change a LARGE area of rock
Mountain Building
CONTACT Process in which rocks
come in contact with magma, causing changes to occur
Small area around magma intrusion
Grades of Metamorphism Low Grade – Low temperature and
pressure (just enough to change). Slate and Phyllite – Small crystals, fine
grained Intermediate – Higher temperature and
pressure than low grade Schist – larger mica crystals
High Grade – Highest Temperature and pressure possible without melting Gneiss – Crystal alignment into bands
Grades of Metamorphism
Foliation and Banding Foliated Rocks – When metamorphism
results in the alignment of crystals into layers. Schist
Banding – When crystals grow in alternating light and dark layers Gneiss
Non-foliated – No alignment of crystals or layering. Marble
Foliation and Banding
Foliation and Banding
Foliation and Banding