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WHAT ARE IGNEOUS, METAMORPHIC AND SEDIMENTARY ROCKS?
What is magma? (again)
A hot mix of molten rock, gases and minerals Common Earth elements like O, Si, Al, Fe, Mg,
Ca, K and Na are found in magma SILICA (SiO2) is the most abundant material in
magma. Silica is often found in sand and quartz
Silica content affects the melting temperature of magma. (which influences viscosity)
What is magma? (again)
Magma experiences partial melting because of its heterogeneous composition. (what does this
mean?)
What is magma? (again)
Fractional Crystallization: Different minerals within magma cool and crystallize under different conditions
Crystallization and partial melting have a reverse relationship. The first minerals to crystallize are the last
minerals to melt
1. Igneous rocks
Igneous rocks form from the crystallization (deposition) of magma
Extrusive igneous rock is typically of a fine grain and is formed during quick cooling
Intrusive igneous rock is typically of a coarse grain and is formed during slow cooling periods
Bowen’s Reaction Series
N. L. Bowen, a Canadian geologist modelled a pattern of mineral crystallization
As temperatures begin to cool, some calcium-rich minerals undergo a continuous change over a long temperature interval and become sodium-rich
Some iron-rich minerals undergo discontinuous change. These minerals undergo abrupt changes in crystallization.
Bowen’s reaction series: (p. 114)
Samples: 35, 33, 34, 30, 32, 22 or 23Samples: 35, 33, 34, 30, 32, 22 or 23
Bowen’s reaction series: (p. 114)
Bowen’s reaction series
As more and more materials crystallize out of cooling magma, the remaining rock becomes concentrated with silica.
Quartz is the last mineral to crystallize out (mainly silica)
IF ROCKS CHANGE THEIR CRYSTALLINE STRUCTURE AND CHEMICAL COMPOSITION AS THEY COOL, WHY DOES OLIVINE EXIST FOR US TO SEE?The simple answer is crystal separation
Bowen’s reaction series: Figure 5-6 (p. 104)
Classifying Igneous Rocks
Mafic rock has low silica content and are rich in iron. They contain plagioclase, biotite, amphibole, pyroxene, and olivine; EX. Gabbro
Felsic rock have high silica content and contain quartz and feldspars
Ultramafic rock contains super-low silica and super high iron.
Sample: 38Sample: 38
Classifying Igneous Rocks
Differences between similar samples such as size, shape, grain size and texture may be described by cooling rates of magma
Mineral grains, rather than rock shape, are used for identification. (why?)
Porphyritic texture describes well-formed crystals surrounded by fine grained crystals of the same or differing material
Igneous Rock for Industry
Interlocking grains give strength Some mineral crystals are naturally
resistant to weathering Granite composition may be
aesthetically pleasing
Igneous ‘Veins’
Some metallic elements like gold, silver, lead and copper are not a part of common minerals and behave in a similar way to silica.
They are the last substances to precipitate out of magma during cooling
Minerals Veins
Large-grain minerals containing rare elements like lithium and beryllium
Type of ultramafic rock (low silica, high elemental metal)
Diamonds form in kimberlite
MIR MINE
Pegmatites Kimberlites
Read section 5.1 on pages 112-117
and answer questions: 1-6
Read section 5.2 on pages 118 – 123
and answer questions 1-4
Read section 5.1 on pages 112-117
and answer questions: 1-6
Read section 5.2 on pages 118 – 123
and answer questions 1-4
2. Sedimentary Rocks
Sediment refers to material that is broken down through weathering and transported by erosion, ice and gravity
These fragments of material stick together to form sedimentary rock
Materials within sedimentary rock vary in their resistance to weathering which produces clastic rock (‘broken’ rock)
Sediments Size
Very small particles
Very large particles
Clay Silt Sand Gravel
Pebble
Cobble
Boulder
Deposition and Lithification
Larger materials deposit first in fluids
Transport by ice does not discriminate between particle sizes
Lithification
Pressure from overlying material force sedimentary rock to compact.
Clay and silt do not allow much space for water, but sand and larger particles do.
Water and materials travel through sedimentary rock into the Earth where temperatures increase by 30˚C every kilometer below the surface
At around 4 kilometers below the Earth’s surface cementation may begin to occur
Lithification occurs through Cementation
1. Unique minerals like Calcite or iron oxide grow in-between sediment grains
2. Existing mineral grains grow larger as more of the same mineral becomes available
Bedding
Bedding refers to the horizontal layering of sedimentary rock through erosion and grain size
Graded-bedding refers to bedding that contains coarse and heavy layers near the bottom layers
Cross-bedding refers to layers of sediment that are inclined and represent sedimentary layers that move horizontally along a surface through the action of wind or water
Clastics: Coarse grain
Particles travelling as bed load become rounded and eventually become conglomerate (rounded and coarse grained clastic)
Angular coarse grained clastic is called breccia
Sample: 54Sample: 54
Clastics: Medium Grain
These rock forms usually come from rivers and streams and form sandstone
Stratification tells scientists the direction of fluid movement
High porosity allows water to move through sandstone and can allow oil, natural gas and groundwater reservoirs to form
Sample: 55Sample: 55
Clastics: Fine Grain
Very low porosity that does not allow for movement of fluids
Forms shaleSample: 56Sample: 56
Sedimentary Rock created through Chemical Process
Chemical Minerals that precipitate out of solution during evaporation are called evaporites
Examples; Halite (salt), calcite (calcium carbonate aka old chalk) and gypsum (calcium sulfate)
Samples: 63, 64Samples: 63, 64
Sedimentary Rock created through Biological Process
Organic Rock formed from the remains of living things
Examples; limestone from organic sea shells and bone
Coal from thick layers of plant material
Read section 6.1 on pages
134 - 140 and answer
questions: 3-6
Read section 6.2 on pages 141 – 144 and answer
questions 1-7
Read section 6.1 on pages
134 - 140 and answer
questions: 3-6
Read section 6.2 on pages 141 – 144 and answer
questions 1-7