Geology Exam

Question 1

How are igneous rocks formed?

Answer 1

From the crystallisation of magma

Question 2

Describe Intrusive igneous rocks

Answer 2

• Solidified Underground
• Slow Cooling
• Large crystals formed

Question 3

Describe Extrusive igneous rocks

Answer 3

• Solidified at surface
• Cooled Quickly
• Small crystals formed

Question 4

Describe Felsic rocks and what minerals they are dominated by, and give 2 examples

Answer 4

• Light coloured
• Low density
• Low melting point
• High viscosity
• Dominated by Quartz and Feldspar
• Granite Intrusive, Rhyolite Extrusive

Question 5

Describe Mafic rocks and what minerals they are dominated by, and give 2 examples

Answer 5

• Dark coloured
• High melting point
• Low viscosity
• Dominated by Magnesium and Olivine
• Basalt Extrusive, Gabbro Intrusive

Question 6

Descibe the properties of Granite, where it occurs, weathering and hydrology

Answer 6

• Felsic igneous
• Intrusive
• Made of Feldspar and Quartz
• Very strong rock, good for foundations
• Forms in large batholiths
• Groundwater only in fractures
• Coarse grained

Question 7

Descibe the properties of Basalt, where it occurs, weathering and hydrology

Answer 7

• Mafic igneous
• Extrusive
• Lava flows in bedded sequences, cooled after flowing from volcano
• Made of Feldspar and Mafics
• Variable strength
• Decays to clay soils
• Fine grained

Question 8

What is a Phenocryst?

Answer 8

a large crystal surrounded by a matrix of finer crystals - It denotes 2 stages of cooling

Question 9

Give the main differences between Rhyolitic and Basaltic lava and give the name of the intermediate

Answer 9

Rhyolitic: Felsic, low temp so low viscosity, high silica content
Basaltic: Mafic, high temperature so low viscosity, low silica content, high speeds
Intermediate = Andesitic lava

Question 10

Describe Clastic Sediments

Answer 10

• Accumulations of clastic particles derived from weathering of pre-existing rocks.
• Often dominated by quartz as it is hard and does not weather
• They are rounded by physical abrasion during transportation
• They are sorted by particle size as they are transported

Question 11

State the difference between laminar flow and turbulent flow

Answer 11

Laminar: Gravity acts on tiny particles which sink to the bottom of river
Turbulent: Keeps particles moving and mixing, so larger particles are able to be transported

Question 12

Name the 3 main chemical sedimentary environments

Answer 12

Carbonate: Deep sea made of shelled organisms
Evaporite: Evaporation of sea water made of nitrates
Swamp: Peat (coal, oil, gas) compresses easily

Question 13

How is cross bedding formed?

Answer 13

Sand is transported by wind which causes slopes, when wind changes direction, slopes form in opposite direction

Question 14

Describe graded bedding

Answer 14

Coarse at base reducing to fine on top as speed of current decreases over time

Question 15

Define Lithification

Answer 15

The turning of sediment into rock

Question 16

Descibe the properties of Limestone, where it occurs, weathering and hydrology

Answer 16

• Sedimentary, chemical carbonate
• Variable sized calcite mosaic, usually with shell fragments
• Made up of calcite
• Occurs in marine shell debris and chemical precipitate
• Soluble in rainwater, allowing for open fissures, sinkholes and caves
• Older limestones are stronger as they are more completely recrystallised, but extreme variability
• Excellent aquifer

Question 17

Descibe the properties of Clay, where it occurs, weathering and hydrology

Answer 17

• Sedimentary, Clastic
• Fine grained
• Older, unweathered clays have higher strength. Weak foundation strength with low, variable strength due to water content
• Aquicude. Fine particles, narrow channel, water doesn’t flow easily