Module 6Module 6

R o c k sR o c k s

RocksRocks

A rock is a naturally formed aggregate A rock is a naturally formed aggregate composed of one or more mineralscomposed of one or more minerals

Rocks are aggregates of one or more Rocks are aggregates of one or more mineralsminerals

What is a What is a rock?rock?

Which one is the best Which one is the best answer?answer?

RocksRocks

Example of a rock, an aggregate of more than one mineralsExample of a rock, an aggregate of more than one minerals

Rocks are classified on the basis ofRocks are classified on the basis ofhow they formhow they form

There are There are 3 major classes 3 major classes of rock: of rock:

Igneous rockIgneous rock Sedimentary rockSedimentary rock Metamorphic rockMetamorphic rock

RocksRocks

Igneous Rocks formed by crystallization of Igneous Rocks formed by crystallization of molten rock materialmolten rock material

Molten rock material below Earth’s surface is Molten rock material below Earth’s surface is called called magmamagma

Molten rock material erupted above Earth’s Molten rock material erupted above Earth’s surface is called surface is called lavalava

The name changes because the composition The name changes because the composition of the molten material of the molten material changes as it is erupted changes as it is erupted due to escape of volatile gasesdue to escape of volatile gases

Igneous RocksIgneous Rocks

• Metamorphic rocks are changed rocksMetamorphic rocks are changed rocks

• They are They are formed in the solid stateformed in the solid state in in response to the following response to the following agents of agents of metamorphismmetamorphism::

• Change in Change in pressurepressure

• Change in Change in temperaturetemperature

• Change in Change in pressurepressure and and temperaturetemperature

Metamorphic RocksMetamorphic Rocks

• The The protolithprotolith (the (the parent rockparent rock) is the ) is the preexisting rock from which the preexisting rock from which the metamorphic rock was formedmetamorphic rock was formed

• Metamorphism may cause a change in a Metamorphism may cause a change in a rock’s: rock’s: • CompositionComposition• Mineral assemblageMineral assemblage• TextureTexture• All of the aboveAll of the above

Metamorphic RocksMetamorphic Rocks

• Rocks formed from material derived from Rocks formed from material derived from preexisting rocks by surfacial processes preexisting rocks by surfacial processes followed by diagenesisfollowed by diagenesis

• There are two main classes of sedimentary There are two main classes of sedimentary rocksrocks ClasticClastic (detrital) sedimentary rocks(detrital) sedimentary rocks Chemical (non-clastic) sedimentary Chemical (non-clastic) sedimentary

rocksrocks

Sedimentary RocksSedimentary Rocks

Clastic sedimentary rocksClastic sedimentary rocks are formed from are formed from bits and pieces of previously existing bits and pieces of previously existing rocks, called clasts or detritusrocks, called clasts or detritus

Chemical (Non-clastic) sedimentary rocksChemical (Non-clastic) sedimentary rocks are formed in several waysare formed in several ways By precipitation from aqueous solutionBy precipitation from aqueous solution From plant materialFrom plant material From animal materialFrom animal material

Sedimentary RocksSedimentary Rocks

Processes Leading to Formation of Processes Leading to Formation of Clastic Sedimentary RocksClastic Sedimentary Rocks

Weathering:Weathering: the processes that change rocks’ size and the processes that change rocks’ size and composition at or near Earth’s surfacecomposition at or near Earth’s surface

Erosion and Transportation:Erosion and Transportation: removal of rock particles removal of rock particles (clasts) from their source by water, wind, or glacial ice(clasts) from their source by water, wind, or glacial ice

Deposition:Deposition: the settling of clasts on Earth’s surface as the settling of clasts on Earth’s surface as sediments, leads to formation of a sedimentary bedsediments, leads to formation of a sedimentary bed

Compaction:Compaction: pressing together of clasts, squeezing out pressing together of clasts, squeezing out pore water, by pressure exerted by overlying bedspore water, by pressure exerted by overlying beds

Lithification:Lithification: cementation of clasts together to form a cementation of clasts together to form a sedimentary rocksedimentary rock

Diagenesis:Diagenesis: a process of conversion of unconsolidated a process of conversion of unconsolidated sediments to coherent sedimentary rockssediments to coherent sedimentary rocks

Sedimentary RocksSedimentary Rocks

Rocks CycleRocks Cycle

RocksRocks

ColorColor: : the first guide to differentiate the first guide to differentiate minerals, texture, and structureminerals, texture, and structure

Mineral compositionMineral composition:: names (with brief names (with brief description) and percentage of individual description) and percentage of individual mineralmineral

TextureTexture:: the relationship between the the relationship between the grains of minerals forming a rock grains of minerals forming a rock

StructureStructure:: the relationship between the relationship between different parts of a rockdifferent parts of a rock

How can you identify rocks How can you identify rocks megascopically?megascopically?