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94 Cards in this Set
- Front
- Back
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What is the crystal size of a fine grained crystal? |
<1mm |
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What size is a crystal in a medium grained rock? |
1-5mm |
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What size is a crystal in a coarse grained rock? |
>5mm |
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What percentage silica content does an ultramafic rock have? |
<45% |
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What percentage silica content does a mafic rock have? |
45-52% |
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What percentage silica content does an intermediate rock have? |
52-66% |
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What percentage silica content does a silicic rock have? |
>66% |
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What colour is a silicic rock normally? |
Lighter coloured |
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What colour is a mafic/ultramafic rock normally? |
Dark coloured |
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Which rock is an exception to the colour-silica content rule? And what colour is it? |
Obsidian, it is black |
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What kind of minerals are rich in silica? |
Felsic |
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What kind of minerals are rich in magnesium and iron? |
Mafic |
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The slower the rate of cooling... the _____ the crystal size. |
Larger |
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The faster the rate of cooling, the ______ the crystal size. |
Smaller |
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What crystal size is always an extrusive rock? |
Fine crystals |
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What crystal size is often an intrusive, hyperbyssal rock |
Medium grain |
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What crystal size is often an intrusive, plutonic rock |
Coarse grain |
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What is a pegmatite? |
An igneous rock with exceptionally large crystals. |
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What is the name of a texture where all crystals are of equal size? |
Equigranular texture |
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What is the name of the texture where there are small holes where gas was present? |
Vesicular texture |
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What is the name of the texture where vesicles have been filled in by another mineral? |
Amygdaloidal |
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What is the name of the hole in a vesicular texture? |
Vesicle |
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What is the name of a vesicle filled in with another mineral in an amygdaloidal texture? |
Amygdale |
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What is the name of the texture where there are large crystals amoungst smaller groundmass? |
Porphyritic texture |
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Why do porphyritic textures have two different sized crystals? |
A rock has two stages of cooling. |
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What is the name of the large crystals in a porphyritic texture? |
Phenocrysts |
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When does flow banding occur? |
Where layers of dark and light coloured minerals form due to the seperation of minerals with a silicic lava flow. |
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Name a rock with flow banding |
Rhyolite |
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What shape are vesicles? |
Ellipsoid, elongated parallel to the direction of flow. |
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Where would you find silicic igneous rocks? |
Convergent plate margins |
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Where would you find intermediate igneous rocks? |
Convergent plate margins |
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Where would you find ultramafic igneous rocks? |
Ophiolites at subduction zones |
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Where would you find mafic igneous rocks? |
Divergent plate margins, and hot spots |
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What is the order of the discontinuous reaction series? |
Olivine, Pyroxene, Hornblende, Biotite Mica |
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What is the order of the continuous reaction series? |
Ca Rich Plagioclase Feldspar, Na Rich Plagioclase Feldspar |
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What minerals will be in ultramafic magma? |
Olivine, Ca Feld, poss Pyroxene |
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What kind of minerals will be in mafi magma? |
Olivine, Pyroxene, Ca Feldspar |
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What kind of minerals will be in intermediate magma? |
Hornblende, Biotite Mica, Na Feldspar |
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What minerals are in silicic magma? |
Potassium feldspar, muscovite mica, quartz |
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Which mineral will crystallise first at high temperatures? |
Olivine |
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Which mineral will crystallise last out of Bowen's reaction series? |
Quartz |
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Do mafic rocks form at high or low temperatures? |
High |
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Do silicic rocks form at high or low temperatures? |
Low |
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Name the three processes of magmatic differentiation. |
Fractional crystallisation, gravity settling, filter pressing |
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What happens to early formed minerals (eg. Olivine) in a magma chamber? |
Sink to form a layer at the bottom of the intrusion |
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What is a layer of dense, early formed minerals at the base of a magma chamber called? |
Cumulate layer |
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Intrusions that run along a bedding plane are concordant/discordant? |
Concordant |
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Intrusions that cross cut a bedding plane are concordant/discordant? |
Discordant |
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What is the name of the rock around an intrusion? |
Country Rock |
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Which rocks are most sills and dykes predominantly made up of? |
Dolerite |
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Which finer grained rock is along the chilled margin of an igneous intrusion? |
Basalt |
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Sheet-like intrusions that are concordant and parallel to the beds. Is this describing a sill or a dyke? |
Sill |
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Sills that cut across beds in steps from one bed to another are called? |
Transgressive Sills |
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Do sills form at shallow or deep depths? |
Shallow depths - where the weight of the overlying rocks is not too great |
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Sheet-like intrusions that are discordant and often vertical. Is this describing sills or dykes? |
Dykes |
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Are most batholiths concordant or discordant? |
Discordant |
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What shape is the outcrop for many batholiths? |
Circular (with steep sides) |
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What are most batholiths composed of? |
Granite |
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Are batholiths plutonic or hyperbyssal? |
Plutonic |
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Where are most batholiths formed? |
Convergent plate margins |
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Whereabouts around the intrusion is a chilled margin? |
The edge of the intrusion, close to the cold country rocks |
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Whereabouts around the intrusion are baked margins? |
The country rock adjacent to an intrusion. |
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Doesa chilled margin have coarse or fine crystals? And why? |
Fine grained crystals because it cooled quickly |
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The larger the intrsion, the _______ the baked margin |
Wider |
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What do metamorphic aureole formed around? |
Batholiths |
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How many chilled margins do sills have? |
Two - due to contact with cointry rock above and below |
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How many baked margins do lava flows have? |
One below and none above - when it was formed there was only air above. |
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Are xenoliths found at sills? |
Yes- from rocks above and below as the sill rips up material. |
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Are vesicles found in lava flows? |
Yes - in the upper part. |
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What is the main gas from a volcanic eruption? |
Water vapour, as steam |
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What is the difference between lava and magma? |
Magma is molten rock below the surface, lava is once its been erupted. |
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Mafic lavas have a high/low viscosity? |
Low |
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Name two types of mafic lavas. |
Pahoehoe and aa lava |
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Lava with a high viscosity is/isn't runny? |
Is not runny |
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Silicic lavas have a high/low viscosity? |
High |
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Name two rocks which come from silicic lavas |
Andesite and rhyolite |
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What can silicic lavas sometimes show? |
Flow banding |
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What is the name and size of the smallest particle of pyroclastic material? |
Ash (<2mm) |
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What does the particle ash from when it is consolidated? |
Tuff |
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Lapilli are particles between ___mm and ___mm, and when consolidated it forms ________. |
Between 2mm and 64mm. Forms lapilli tuff. |
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What are the names and sizes of the largest particles of pyroclastic material? |
Bombs and blocks (>64mm) |
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What do bombs and blocks form when they have been consolidated? |
Agglomerate |
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Name three variables that affect how far away pyroclastic matetial will settle. |
Any of: Energy of the volcanic blast Grain size of the particles Velocity and direction of wind Gradient of volcano Magma viscosity |
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What are lahars? |
Mudflows of wet ash and volcanic debris that can flow rapidly down a mountainside. |
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Do mafic volcanoes have explosive reactions? |
No |
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Are eruptions from mafic volcanoes frequent? |
Yes |
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Shield volcanoes have gentle slopes of less than ___ degrees. |
10 degrees |
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What is the name of the eruption where magma reaches the surface along long, linear cracks? |
Fissure eruptions |
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Describe how columnar jointing occurs. |
Inside of flow cools steadily, causing lava to contract. This makes columns with equally spaced centres. |
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Can pillow lavas be used as a way up structure? |
Yes - they have rounded tops and a sagging bottom |
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The VEI (Volcanic Explosivity Index) goes from ___ to ___. |
0-8 |
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Why do stratovolcanoes have such explosive eruptions. |
They have a high gas content, but the high viscosity does not allow the gases to break through. |
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Name three methods of predicting volcanic activity. |
Any of: Ground deformation Historic pattern of activity Gas emissions Changes in groundwater Seismicity |
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Name three of the benefits of living with volcanic activity. |
Any of: Geothermal power Fertile soils Building materials Minerals |
