OCR Geology - A-Level: Module 2

What is a *mineral*?

A *naturally occurring chemical* substance having a *definite composition* and *crystalline structure* e.g. Quartz

List the *diagnostic properties* used to *classify* minerals

- Colour
- Streak
- Shape
- Lustre
- Cleavage and Fracture
- Hardness
- Density
- Reaction to Acid
- Magnetism

Name a *difference* between *rocks* and *minerals*

A *mineral* is *naturally occurring* having a *definite structure* being a *compound* whereas a *rock* is a *mixture*

Name the *two* ways *minerals form*

1. *Grow from liquids* such as magma or groundwater
2. From *solid state recrystallisation*

How do minerals *grow?*

They add to their *faces*. If they *develop unrestricted* the atoms have a *regular arrangement*, the *angle* is always *constant*.

What is *Pyrite?*

A *mineral* bonded with *sulphur*

What is *Calcite* and *Quartz?*

A *mineral* bonded with *oxygen*

What is a *single tetrahedra* silicon:oxygen ratio?

1:4

What is a *chains* silicon:oxygen ratio?

1:3

What is a *double chains* silicon:oxygen ratio?

4:11

What is a *sheets* silicon:oxygen ratio?

2:5

What is a *frameworks* silicon:oxygen ratio?

1:2

What is *polymerisation?*

Polymerisation is when *silicate tetrahedra* are joined to make *polymers*

What is the difference between *biotite* and *muscovite mica?*

Muscovite mica is white and biotite mica is dark and almost black

How do you perform a *hardness test?*

You *scratch* the mineral with different objects. If the mineral can scratch *glass it 7-10* on the scale but if the mineral can be scratched by a *fingernail it's 1*

What does *vitreous* mean?

*Shiny* and *reflective*

What does *dull* mean?

An *earthy lustre* that *doesn't* reflect light

Define the term *conchoidal fracture*

Describes the way *brittle material breaks* or *fractures* and *doesn't follow the natural plains of separation*

How are *sedimentary rocks* formed?

Compaction, cementation, lithification

What's the difference between clastic and non-clastic sediment?

- Clastic sediment is composed of fragments, formed by weathering processes left with debris.
- Non-clastic sediment is rock formed through chemical reactions etc.

How are *igneous rocks* formed?

Magma and lava are molten materials that harden and form this type of rock

How are *metamorphic rocks* formed?

Heat and pressure

What is the *Phanerozoic* Eon?

The *length of time* during which *fossils* with *hard parts* are found

What is the *Phanerozoic Eon divided* into?

Paleozoic, Mesozoic, and Cenozoic eras

What is the *Cenozoic* era made up of?

Quaternary, Neogene and Palaeogene

What is the *mesozoic* era made up of?

Cretaceous, Jurassic and Triassic

What is the *Paleozoic* era made up of?

Permian, Carboniferous, Devonian, Silurian, Ordovician and Cambrian

Name the *three main mass extinctions?*

The Cambrian Explosion, PT Extinction, K-T Extinction

How *old* is the *Earth?*

*4.58 billion years* old

What is the *geological column?*

It's a graph representing the *vertical distribution* of rock ages based on *recognition* of *fossil types.*

What is *catastrophism?*

*Large scale formation* of rocks from *sudden* and *short lived events*

What is *gradualism?*

The theory that *evolution occurs slowly but steadily*, variation is a *gradual event* along with processes

What is *uniformitarianism?*

The *processes* happening are the *same* that happened *in the past.*

What *areas* are *uniformitarianism limited in?*

- Climate and atmospheric chemistry
- Plate tectonics
- Continental drift
- Oceanic circulation and chemistry
- Ecosystems
- Planetary geology
- Catastrophic events

Explain the meaning of the term *'half life'*

*Time taken* for *halve the unstable parent atoms to decay and form stable daughter products*, time for it to reduce by *50%*

What is *radiometric dating?*

The process of determining the *age* of the fossils from *radioactive isotopes*

What are the two *methods of dating?*

*Relative* and *absolute*

Whats the *difference* between *relative* and *absolute* dating?

*Relative dating* is putting rocks in *order of age* separating them *by events* like metamorphism

*Absolute dating* is the *absolute timescale* of rocks used to measure ages of *correlated rock* around the world.

How are *absolute ages measured?*

Using *half-lives* to measure *how many have passed* since the *parents formed*

What is a *closed system?*

Rocks *not subject to later change* after *closure temperature* has *changed*

What is a *closure temperature?*

Temperature at which the *parent isotopes* become *fixed*

What is *Potassium-Argon* and *Rubidium-Stronium dating?*

Most used method of dating compared

What are some *problems* with *radiometric dating?*

- Major intrusions take *millions of years to cool*
- Different parts reach *different closure temperatures* at *different times*
- Sedimentary rock could have *different clasts of different ages*
- Sedimentary rock more *prone to weathering* altering *parent daughter ratio*
- Metamorphic rocks could have *different closed systems at different times,* parent and daughter cells can be *lost at different times*

What are the *factors* that affect *fossilisation?*

Conditions during life, death, transport and burial, dependant on taphonomic processes (biological, chemical and physical processes)

Name the *five* types of *preservation* of fossils

- Replacement
- Silicification
- Carbonisation
- Pyritisation
- Mould and cast

What's a trace fossil?

A fossil of a footprint, trail, burrow, or other trace of an animal rather than of the animal itself

How are trace fossils made?

When an organism makes a mark in mud or sand. The sediment dries and hardens over the top leaving a print

Name the six types of trace fossils

- Tracks
- Trails
- Burrows
- Borings
- Excrement
- Root structures

What is a benthonic environment?

Organism lives on or in the sediment substrate of the sea floor

What is the pelagic environment?

Organism lives in the water column typically in the surface layers

Name five palaeo-environments

- High energy continental shelf
- High energy shallow marine
- Low energy shallow marine
- Low energy deep marine
- Low energy deltaic/terrestrial

What is a cephalopods morphology?

- Chambered shells, adjusting ratio of gas
- Live in a pelagic environment and is nektonic

What is a corals morphology?

- First seen in the odvocian, some the cambrian depending on the morphology
-Some strands extinct but are modern fossils around, first seen triassic

What is a bivalves morphology?

- Benthonic habitats
- Similar to the brachiopod morphology
- Common in the Palaeozoic era just made it through the PT extinction

What is a trilobites morphology?

- Arthropods with a chitin exoskeleton
- Divided into three sections
- Evolved in the Cambrian and became extinct in the Permian Period

What is a brachiopods morphology?

- Long-hinged species, free-lying on the sea floor
- Have different valve sizes

Name the three methods of classifying igneous rocks

- Crystal size
- Mineral composition
- Silica percentage

What is the grain size of a fine grained rock?

\>1 mm

What is the grain size of a medium grained rock?

1 - 5 mm

What is the grain size of a coarse grained rock?

Name the four classifications of igneous rocks

- Silica Content
- Grain size
- Colour
- Mineralogy

Higher silica content

Higher viscosity, lighter colour

Lower silica content

Lower viscosity, darker colour

If a rock has \>66% in silica content what's it called? Name the examples:

- Silicic
- Obsidian, Pumice, Rhyolite and Granite

If a rock has a silica content of 52 - 66% whats it classified as? Name some examples:

- Intermediate
- Andesite and Pumice

If a rock has a silica content of

- Ultramafic
- Peridotite

If a rock has a silica content of 45 - 52% whats it classified as? Name some examples:

- Mafic
- Basalt, Dolerite and Gabbro

What does the igneous classification table look like?

What's a pegmatite?

Coarse crystalline granite or igneous rock with crystals several centimetres of length

How is crystal grain shape affected in igneous rocks?

The rate of cooling:
Slow \= Euhedral pagioclase, sub-equant olivine, and prismatic pyroxene, enough time to add to their faces

Name an example of a glassy rock:

Obsidian

Name the seven textures of igneous rocks:

- Equicrystalline/Equigranular
- Porphyritic
- Vesicular
- Amygdaloidal
- Flow banding
- Ophitic
- Cumulate

Name three ways sedimentary rock forms

- Chemical weathering
- Mechanical weathering
- Biological weathering

What happens to weathered material?

Some remains where it is and the rest will be transported away

Transport can be due to:

- Gravity
- Wind
- Rivers
- The sea
- Ice

Name some methods of transport:

- Suspension
- Saltation
- Traction

Grain Shape - Roundness

The rounder they are the more transport has taken place

Grain size

The size of the grains that make up a rock, which helps to classify the type of rock and maturity

What does the analysis of sediments tell us?

- Size, range and roundness of sediments
- Fine grained, well rounded transported for a longer time
- How sediment has been transported

Mineralogical Maturity

A measure of the extent to which minerals have been destroyed by weathering and attrition

Grains Size, Shape and Sorting using wind as transport in a desert environment

- Transport process suspension, grain size fine - medium
- Well rounded, attrition only takes place
- Well sorted

Grains Size, Shape, Sorting and transport in a glacial environment

- Boulders, medium to large grain size
- Sub-angular, no erosional processes can take place
- Poorly sorted sediment

Grains Size, Shape, Sorting and transport in a fluvial environment

- All four erosional and transport processes
- Clay to boulders, depends on how far along the fluvial environment you are
- Poorly sorted, well rounded - angular grains

Grains Size, Shape, Sorting and transport in a marine environment

- All transport types clay - boulders
- Sub angular - Angular
- Poorly sorted, no transport processes

Super mature sediment

- Well rounded - rounded
- Well sorted
- Monomineralic

Mature sediment

- Rounded - Sub rounded
- Moderately sorted
- Several different minerals

Immature sediment

- Sub-angular to angular
- Poorly sorted
- Lithic

Dichotomous tree

Tool used to classify rocks into their correct grouping using specific characteristics

classifying sedimentary rocks

sedimentary rocks are classified according to the size, shape, and composition of their constituent particles.

Two main groups of sedimentary rock:

1. Mechanically formed sedimentary rocks
2. Carbonates ie, grains and cement of CaCo3

What's the formation order of sedimentary rocks?

Weathering - Erosion - Transport - Deposition - Burial - Diagenesis

What are three descriptions of mechanically formed sedimentary rocks?

- Siliciclastic
- Bioclastic
- Pyroclastic

Breccia

coarse sedimentary rock consisting of angular fragments; or rock broken into angular fragments by faulting
- Rock Fragments
- Quartz
- Mica
- Muddy matrix

Desert sandstone

Clastic sedimentary rock, dominated by quartz and red in colour due to haematite content. Medium sized, well rounded and well sorted grains.
- Quartz
- Fe2O3 cement

Conglomerate

a coarse-grained sedimentary rock composed of rounded fragments (\> 2 mm) within a matrix of finer grained material.
- Shell fragments
- Matrix
- Quartz

Arkose

A clastic sedimentary rock containing both quartz and feldspar grains, coarse

Orthoquartzite

A very pure quartz sandstone composed of usually well rounded quartz grains cemented by silica. Often 99% SiO2

Greywacke

A dark coarse-grained sandstone containing more than 15 percent clay.
- Quartz grain
- Quartz cement

Mudstone/Shale

-clay mineral and mica
-

Clay

the finest soil, made up of particles that are less than 0.002 mm in diameter.