Surface Features in New Zealand

Science NCEA 1.13

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Cross-section of the EarthTheory of plate tectonicsSea floor spreading and subduction zonesEarthquake and volcanic activityVolcanic forms and formationMountain upliftWeatheringErosionFossil formation and datingStratigraphic column analysisGeological events –faulting, subduction, deposition, igneous

intrusionMain rock types and formationThe rock cycle

Objectives

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The thin layer of solid rock which covers the Earth is called the crust.

What does the Earths interior look like?

The crust is made up of the thick continental crust that forms the land and the much thinner oceanic crust that makes up ocean floors.

What does the Earths interior look like?

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Under this is the mantle. The middle of this is molten - so the upper mantle and crust float on this.

What does the Earths interior look like?

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The inner layer is the core, which is a solid core surrounded by molten rock.

What does the Earths interior look like?

When earthquakes occur they send waves through the earth. Different types of material with different temperatures will cause the waves to bend in different ways.Seismologists (earthquake scientists) record where in the world the waves come out and use that information to work out the size of layers, what the temperature of them is and what they are made out of.

How do we know what the Earths interior look like?

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The earth’s crust is divided into different sized pieces called plates. They fit together to cover the earth.

Plate Tectonics

The plates float on hot, semi molten magma

Deep in earths core nuclear reactions release huge amounts of heat energy. This heat is the main source of energy for moving the gigantic plates

This heat causes the magma in the lower mantle rock to expand and become less dense.

This magma rises in convection currents

When the magma currents get near the crust they are pushed sideways and travel in different directions

These immensely powerful currents slowly float the huge tectonic plates across the planets surface

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Plate Tectonics

The Lithosphere, the crust and top part of the mantle, is divided into large areas called plates, which are constantly moving

The plates move slowly over the asthenosphere, which is the molten layer in the mantle, about 3cm a year.

They can move towards each other, apart from each other or shift sideways

Because all plates fit together, movement of one plate effects all plates around it

The study of plate movement is called plate tectonics

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Plate Tectonics

Evidence supports the conclusion that 200 million years ago, at the start of the Mesozoic era, all the continents were attached to one another in a single land mass, which has been named Pangaea.

During the Triassic, Pangaea began to break up, first into two major land masses:

Laurasia in the Northern Hemisphere and

Gondwana in the Southern Hemisphere.

The present continents separated at intervals throughout the remainder of the Mesozoic and through the Cenozoic, eventually reaching the positions they have today. Gaz

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Evidence for Plate Tectonics

Shape of the Continents – close fit of continents The east coast of South America and the west coast of Africa

match especially at the boundaries of the continental slopes rather than the shorelines.

Geology – similar rock patterns In both mineral content and age, the rocks on the coast of

Brazil match precisely those found on the west coast of Africa.

The low mountain ranges and rock types in North America match parts of Great Britain, France, and Scandinavia.

Fossils – patterns in distribution The same fossil reptiles found in South Africa are also found

in Brazil and Argentina.

Evidence for Plate Tectonics

The continents have gradually moved from one large land mass into the continents we know today. This movement has been slow but the time scale is large. The continents are still moving today.

Evidence for Plate Tectonics

Plate Tectonics

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When plates move the continents sitting on top of them move as well. Plates can either; Move away from each other –

divergent boundary Move towards each other –

convergent boundary

Move sideward pass each other – transverse boundary

Plate Movement

A divergent boundary is where the tectonic plates are separating.

New crust is made from cooling magma oozing up between the plates

Some spreading boundaries are places where the crust is sinking downward as it is stretched thin

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Divergent Boundary

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A Convergent Boundary is the opposite of a divergent boundary. Typically you will see a converging boundary on a tectonic plate that is on the opposite side of a divergent boundary

Convergent Boundary

Sometimes you'll see volcanic activity at converging boundaries where plates are crashing into each other.

When one plate (usually the lighter continental crust) rides up over the top of the other it's called a Subduction zone

one plate margin slides under the other and melts into magma as it moves downwards

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Convergent Boundary

As a plate moves in one direction it collides with the adjacent plate on its "front" end, while the trailing end of the plate is being pulled and stretched (spreading) from the plate on the other end.The colliding plates can cause a pushing up of land and the forming of a mountain range along the edge of a plate.

Convergent Boundary

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Transform fault boundaries are places where the two plates are just sliding past each other. Of major importance are the earthquakes that are triggered along fault boundaries.

Transform fault Boundary

Aerial view of the San Andreas fault slicing through the Carrizo Plain in the Temblor Range

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Fault seen through plantation

Transform fault Boundary

Plate Boundary Summary

Divergent Boundary

Convergent Boundary

Transform plate Boundary

Plate Boundary Summary

New mountains are built when rocks are pushed upward by movement of the tectonic plates.

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Mountain uplift

Mountains can also be made when the ground is pushed up by plate movement

Fold mountains are formed when layers of rock become buckled

Mountain uplift

Block mountains are formed when giant lumps of rock rise or fall

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Mountain uplift

Volcanic eruptions also create mountains. Lava and ash left behind after an eruption remain as land and mountains

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Mountain uplift

When tectonic plates collide, one plate may slide below the other (called the subduction zone).

The sinking plate melts from heat created by friction.

Magma is produced and may force its way to the surface, creating a volcano.

The explosive effect is known as an eruption.

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Volcanic eruptions

Mt Ruapehu erupting Gaze

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Shield Volcanoes  are built almost entirely of fluid lava flows.  During their formation, flow after flow pours out of the volcano's vent in all directions. This results in a broad, gently sloping cone with flat conical shape, which looks a little like the shield of an ancient warrior. Some of the largest volcanoes in the world are Shield Volcanoes. The Hawaiian Islands are composed of linear chains of Shield Volcanoes.

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Shield Volcanoes

Earthquakes occur when two tectonic plates move suddenly against each other. The rocks usually break underground at the hypocentre and the earth shakes. Waves spread from the epicentre, and the point on the surface above the hypocentre. If a quake occurs under the sea it can cause a tsunami.

What causes earthquakes

In a strike-slip fault, the blocks of rock move in opposite horizontal directions. These faults form when crust pieces slide along each other at a transform plate boundary.

As plates move the strain causes brittle rock to crackThese cracks, called faults, are often weak zones where more movement

or cracking may occurConstant movement of plates causes pressure to build up at faults, and at

the boundaries of the platesIf there is a sudden slippage of rock, this pressure is released quickly and

an earthquake occurs

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What causes earthquakes

The Alpine fault

The Alpine Fault, is about 600km through the middle of the South Island. It’s the boundary of the Pacific and Australian Plates.Horizontal movement of the Alpine Fault is about 30m per 1000 years, very fast by global standards.A new fault line was discovered when the February 22 Earthquake occurred in Christchurch. This was an extension off the Alpine fault and was in the form of a strike slip fault

Earthquake waves

There are 3 main types of seismic waves are generated when faulting triggers an earthquake. All the seismic waves are generated at the same time, but travel at different speeds and in different ways. Body waves penetrate the earth and travel through it, while surface waves travel along the surface of the ground.

Primary and secondary waves are body waves. Primary waves (P-waves) travel the fastest and can move through solids and liquids. The P-wave energy causes the ground to move in a compressional motion in the same direction that the wave is traveling. Secondary waves (S-waves) are slower and travel only through solids. The S-wave energy causes the ground to move in a shearing motion perpendicular to the direction of wave movement.

Earthquake waves

Surface waves can cause rolling motion or sideways movement. These waves results in ground heave and swaying buildings. Surface waves cause the most devastating damage to buildings, bridges, and highways.

Liquefaction

New Zealand is on the top of two plates moving with transverse motion.

Why Does NZ have so many earthquakes?

Types of rocks

Appearance Silica Rich Intermediate

Silica poor Volcanic Glass

Fine grained (volcanic) rhyolite

pumiceandesite basalt

scoriaobsidian

Coarse grained(plutonic)

granite diorite gabbro

slate schist marble gneiss

conglomerate sandstone siltstone

mudstone coal limestone

Igneous

Metamorphic

Sedimentary

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pumice rhyolite andesite basalt obsidian

scoria granite diorite gabbro

gneiss marble slate schist

Igne

ous

Met

amor

phic

Sedi

men

tary

conglomerate sandstone siltstone

mudstone coal limestone

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Types of rocks

igneous sedimentary metamorphicThe outside of the cooling Earth grew hard formed a crust and turned into rocks. These rocks are called igneous rocks meaning “made by fire”. Sometimes hot, molten rock called magma rises up towards the surface. Some of it cools down inside the crust and becomes the hard rock granite.Sometimes the molten liquid rock bursts out from volcanoes, when it is called lava. The lava cools down to form different rocks, depending on how quickly it cools.

The mud, sand and stones carried by rivers, glaciers and the waves of the sea eventually pile up in thick layers on the bottom of rivers, lakes or the sea. As the sediment builds up, the first layers are compressed by the great weight of those layers that form above them. The new rocks, formed from rocks that were eroded elsewhere, are called sedimentary rocks. They occur in layers called strata and you can sometimes see these strata in cliffs and the sides of quarries. Sedimentary rocks also often have fossils in them.

Some rocks were once other kinds of rocks but they were changed by the heat and great pressures inside the Earth. The great heat involved in forming metamorphic rocks often creates new minerals. The original rock may melt and all the impurities may then come together and form new minerals such as garnets. Occasionally, when coal layers are heated by igneous rocks, then diamonds are formed.

Types of rocks

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Types of rocks

HardnessCan the sample be scratched by a fingernail, a copper coin or by a knife blade, or will it scratch glass?

TextureDoes the sample look grainy or smooth when observed under a hand lens? Is the grain fine or course?

Acid reactionWill a drop of dilute acid cause the rock to fizz? (this indicates the sample contains calcium carbonate)

TransparencyIs the sample transparent (can see through), translucent (can see some of the way through) or opaque? (can’t see through)

Properties used in

identifying rock types

Crystalline structureDoes the sample have the sharp edges and flat faces of a crystal? Does the sample cleave (split) in certain planes?

MagnetismWill moving the sample back and forward affect the needle of a compass placed nearby or not?

Relative densityHow does the mass of the rock sample compare with the mass of a similar volume of water? (lighter, similar or heavier)

Colour and lustreWhat colour is a clean surface of the sample? Is a cleaned surface of the sample shiny, dull or greasy?

HardnessCan the sample be scratched by a fingernail, a copper coin or by a knife blade, or will it scratch glass?

TextureDoes the sample look grainy or smooth when observed under a hand lens? Is the grain fine or course?

Acid reactionWill a drop of dilute acid cause the rock to fizz? (this indicates the sample contains calcium carbonate)

TransparencyIs the sample transparent (can see through), translucent (can see some of the way through) or opaque? (can’t see through)

Properties used in

identifying rock types

Crystalline structureDoes the sample have the sharp edges and flat faces of a crystal? Does the sample cleave (split) in certain planes?

MagnetismWill moving the sample back and forward affect the needle of a compass placed nearby or not?

Relative densityHow does the mass of the rock sample compare with the mass of a similar volume of water? (lighter, similar or heavier)

Colour and lustreWhat colour is a clean surface of the sample? Is a cleaned surface of the sample shiny, dull or greasy?

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Volcanic(extrusive)

Plutonic (intrusive)

obsidian

rhyolite

andesite

basalt

granitediorite gabbro

Scoria

Pumice

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Classification of Igneous Rocks

Volcanic (or Extrusive) igneous rocks form when molten rock reaches the earth's surface and cools. Air and moisture cool the lava rapidly. The quick cooling doesn't allow the formation of large crystals, so most volcanic rocks have small crystals or none at all. In some volcanic rocks, like pumice and scoria, air and other gases are trapped in the lava as it cools. We can see holes remaining in the rock where the bubbles of gas were located.

Vol c anic igneous Pl utonic Igneous

With Plutonic (Intrusive) igneous rocks the molten rock cools before it reaches the surface. Molten rock that is still underground is called magma. Magma originates from the melting of Earth's crust and upper mantle. This melting occurs about a depth of 60 to 200 km. Molten rock that cools before it reaches the surface hardens to become plutonic igneous rock. Because it forms deep beneath Earth's surface, it has more time to cool and it develops large crystals.

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Classification of Igneous Rocks

coal

Related to water flow Mudstone is a fine-grained rock whose original particles were clays or muds. Mud rocks, such as mudstone and shale (that show layers) comprise some 65% of all sedimentary rocks. Mudstone may show cracks or fissures, like a sun-baked clay deposit. Siltstone is a sedimentary rock which has a composition intermediate in grain size between the coarser sandstones and the finer mudstones.Sandstone is composed mainly of sand-size grains. Sandstone may be any colour. Because of the hardness of the individual grains, uniformity of grain size, sandstone is an excellent material for building and pavingA conglomerate is a rock consisting of individual stones that have become cemented together. Conglomerates consist of rounded fragments.

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Classification of Sedimentary Rocks

Related to water flow Mudstone is a fine-grained rock whose original particles were clays or muds. Mud rocks, such as mudstone and shale (that show layers) comprise some 65% of all sedimentary rocks. Mudstone may show cracks or fissures, like a sun-baked clay deposit.

Sandstone is composed mainly of sand-size grains. Sandstone may be any colour. Because of the hardness of the individual grains, uniformity of grain size, sandstone is an excellent material for building and paving

Siltstone is a sedimentary rock which has a composition intermediate in grain size between the coarser sandstones and the finer mudstones.

Increasing Grain (clast) size

A conglomerate is a rock consisting of individual stones that have become cemented together. Conglomerates consist of rounded fragments.

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Classification of Sedimentary Rocks

coal

Related to environment

Coal is a fossil fuel formed in swamps where plant remains decay slowly without oxygen. It is composed primarily of carbon. It is the largest single source of fuel for the generation of electricity world-wide, as well as the largest source of carbon dioxide emissions. Coal is extracted from the ground by coal mining either underground mining or open cast mines.

Limestone composed largely of calcium carbonate. The primary source of limestone is most commonly marine organisms. These organisms secrete shells that are deposited on ocean floors. This layer of sediments is covered by further sediments, which over time with heat and pressure is changed into limestone. Limestone is revealed when Earth movements uplift the rock.

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Classification of Sedimentary Rocks

Related to environment

Coal is a fossil fuel formed in swamps where plant remains decay slowly without oxygen. It is composed primarily of carbon. It is the largest single source of fuel for the generation of electricity world-wide, as well as the largest source of carbon dioxide emissions. Coal is extracted from the ground by coal mining either underground mining or open cast mines.

Limestone composed largely of calcium carbonate. The primary source of limestone is most commonly marine organisms. These organisms secrete shells that are deposited on ocean floors. This layer of sediments is covered by further sediments, which over time with heat and pressure is changed into limestone. Limestone is revealed when Earth movements uplift the rock.

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Classification of Sedimentary Rocks

Gneiss

Marble

Schist

Slate

Granite

Limestone

MudstoneSiltstone

Basalt

Classification of Metamorphic Rocks

MagmaRising under Pressure

Slow cooling under crust – large crystalsEruption or lava flow

Lava

Very fast cooling – no crystals

fast cooling – small crystals

Obsidian

Volc

anic

– E

xtru

sive

Pul

toni

c - I

ntru

sive

Pumice Scoria

Gas bubblesrhyolite

andesite

basalt

gabbro

diorite

granite

Mafic – dark coloured

Felsic – light coloured

decr

easi

ng s

ilica

Increasing viscosity

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Classification of igneous Rocks

Fo r mat io n o f ign eo us r o c k svolcanic: basalt, rhyolite, andesite, scoria, pumice, obsidian

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Formation of Igneous Rocks

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The behavior of a lava flow depends primarily on its viscosity (resistance to flow), slope of the ground over which it travels, and the rate of lava eruption. Because basalt contains the least amount of silica and erupts at the highest temperature compared to the other types of lava, it has the lowest viscosity (the least resistance to flow). Thus, basalt lava moves over the ground easily, even down gentle slopes. Dacite and rhyolite lava, however, tend to pile up around a vent to form short, stubby flows or mound-shaped domes. Gaz

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Volcanic rocks are typically divided into four basic types according to the amount of silica (SiO2) in the rock

The bar graph shows the average concentration of each major element for the four basic types of volcanic rock.

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M………….Rising under Pressure

Slow cooling under crust – large crystalsEruption or lava flow

L……….

Very fast cooling – no crystals

fast cooling – small crystals

O…………

V…

……

…. –

E…

……

….

P…

……

.. –

I……

……

P………….

S………….

Gas bubblesR…………

A…………

B……..

G……….

D……….

G……….

Mafic – dark coloured

Felsic – light coloured

decr

easi

ng s

ilica

Increasing viscosity

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Formation of Igneous Rocks

Weathering and Erosion

Deposition Compaction and

Cementation

uplift

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Formation of Sedimentary Rocks

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Formation of Sedimentary Rocks

Metamorphic Rock

Deposition

Mudstone

Rel

ated

to w

ater

flow

Compaction and Cementation

Siltstone

Sandstone

Coal Limestone

Igneous Rock

plants Marine organism

s

Pressure over time

Conglomerate

Rel

ated

to e

nviro

nmen

t

Parent material

Environmental forcesWeathering and Erosion

Uplift (Geological forces) and Exposure (environmental forces)

Increasing particle (clast) size

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Transportation

Formation of Sedimentary Rocks

M…………… R………….

D……………….

M…………..

Rel

ated

to w

ater

flow

C……………. and C………………..

S……………

S…………….

C………..

L……………..

I………….. R………

P………. M…………..O……

……..

Pressure over time

C………………..

Rel

ated

to e

nviro

nmen

t

Parent material

Environmental forces

W………… and E…………..

Uplift (G………….. forces) and Exposure (E……………… forces)

Increasing particle (clast) size

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Coal is formed when peat is altered physically and chemically. During coal formation, peat undergoes several changes as a result of bacterial decay, compaction, heat, and time. Peat deposits are formed from plant parts (roots, bark, spores, etc) and decayed plants.

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For the peat to become coal, it must be buried by sediment. Burial compacts the peat and causes water to be squeezed out. The coal becomes more and more carbon-rich as the other elements move out.Finally we mine the coal from the ground.

Coal Formation

The deposit becomes more and more carbon-rich as the other elements disperse. The stages of this trend proceed from plant debris through peat, lignite, sub-bituminous coal, bituminous coal, anthracite coal, to graphite (a pure carbon mineral).

For the peat to become coal, it must be buried by sediment. Burial compacts the peat and, consequently, much water is squeezed out during the first stages of burial. Continued burial and the addition of heat and time cause the complex hydrocarbon compounds in the peat to break down and alter in a variety of ways.

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Coal Formation

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Limestone Formation

Sedimentary Rock

Low Grade pressure and temperature

Igneous Rock

Parent rocks

Basalt GraniteLimestoneMudstoneSiltstone

Metamorphic rocks

High Grade pressure and temperature

Slate

Schist Marble Gneiss

Igneous Rock

Mountain building

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Formation of Metamorphic Rocks

S………………… Rock

Low Grade P……………. and T…………………

I……….Rock

Parent rocks

B………. G………L…………..M………...S………..

Metamorphic rocks

High Grade P……………….. and T……………………

S…………

S……..... M........... G……......

I………. Rock

Mountain building

Formation of Metamorphic Rocks

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Formation of Metamorphic Rocks

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Formation of Metamorphic Rocks

•  contact metamorphism a change in the texture, structure, or chemical composition of a rock due to contact with magma   •  regional metamorphism a change in the texture, structure, or chemical composition of a rock due to changes in temperature and pressure over a large area, generally are a result of tectonic forces

Types of Contact Metamorphism

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Contact vs Regional Metamorphism

Large pieces of rock are broken down by natural processes. These include:Rain – the water wears away the rockWind – particles of rock are worn awayIce – the frozen water gets into the rock and cracks it into smaller piecesTemperature changes – from changes of seasonsMechanical weatheringChemical weatheringBiological weathering

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Break down of Rocks

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Rock Cycle

Magma

Melting

MeltingCooling

Heat and pressure

Heat and pressure

Recrystalisation

Recrystalisation

Crystalisation

Sediment

Metamorphic Rock

Weathering and Erosion

Igneous Rock Weathering

and Erosion

Sedimentary Rock

Weathering and Erosion

Sedimentary rock

Sedimentary RockMetamorphic rock

Igneous rock

Compaction and Cementation

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Rock Cycle

Magma

M……..

M……..C……..

H…… and P………

H….. and P………..

R……………….

C……………..

C…………… and C……….

Sediment

Metamorphic Rock

W………….. and E……….

Igneous Rock W……………

and E……….

Sedimentary Rock

W…………..and E……….

S…………….rock

Sedimentary RockM…………… rock

I……….. rock

R………………..

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Rock Cycle

The 4,550 million years of Earth’s history has been divided into geological periods, each defined by the type of species present.The longest period was the precambrian. In this time only bacteria and single celled organisms were found to have existed. There is not much evidence of any remains due to geological processes and earth movement occurring during and since this time.Many periods came to a close due to a mass extinction event. This left the way open for the remaining species to take advantage of the available niches and rapid adaptation could take place producing new species.

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Geological time

We can use the fossils of species found in rock to help us determine the relative age. Similar types of species can be found in most places in the world. Gaz

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Geological time

Geological processes over time will cause a change and/or deformity of the original rock.Some of these changes include; - plate movement creating both faults and uplift of rock-volcanic activity causing new formation of igneous rock on top of or through older rock

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Geological time

Earth processes cause the types and arrangement of rocks to change as well. We can look at these changes and help us understand past events.

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Changing landscape

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Stratigraphic columns

Stratigraphic columns give a cross-section through the rock.The older rocks are to be found at the bottom. Faults cut through the older layers of rock.Volcanic intrusions are newer than the rock they push through.Types of fossils present can also help us find the age of rock types relative to others.

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Stratigraphic columns

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Stratigraphic columns

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Stratigraphic columns

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Stratigraphic columns

Fossils are the remains or traces of an animal or plant that are preserved in rock.

They may come in many forms, from footprints and faint impressions to shells and bones

Only a small proportion of all dead plants and animals find the right conditions to be fossilised

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Fossilisation

Petrification occurs when a living object is slowly turned to stone of a huge number of years.

Minerals seep through the organic matter is an object, filling it completely.

Then the organic matter rots away, but a mineral version of the fossil is left.

This process usually works best in the fossilization of trees.

Some of the most famous petrified trees contain huge rings that describe ancient eras

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Petrification

Molds are literally molds of an animal.

Sometimes animals became trapped in mud, dirt or clay. Then their bodies deteriorated, leaving behind their shape and size in the ground.

A mold can be created in two ways.

An organism can deteriorate and leave a hole showing details of its body.

Or a hollow object, such as a shell, can become filled with matter. When the object deteriorates, the matter filling it is left behind as a mold.

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Molds

Have you ever seen a

dinosaur's footprint? These are formed when mud, clay or silt containing an imprint made by an animal turns to stone.

This is an example of an impression, or the impression that an animal leaves in soft matter.

These fossils are useful in determining weight and structure of ancient animals. Sometimes, even toenails and pores can be seen!

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Impressions

The sea bed contains perhaps the most fossils on the earth.

This is because the soft ground under the sea is made of sedimentary rock, or rock that is composed of layers of land.

When sea creatures die, they drift to the bottom of the ocean and are covered with a layer of sand.

In time, a volcano or mudslide, etc., may cover the surface under which they are buried.

In this way, a new layer is added, and the fossil is preserved in layers of time.

Fossils in sedimentary layers are useful in indicating when land was above and below ground.

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Sedimentary fossils

Andesite is an extrusive rock intermediate in composition between rhyolite and basalt. Andesite lava is of moderate viscosity and forms thick lava flows and domes. The word andesite is derived from the Andes Mountains in South America, where andesite is common. Andesite is the volcanic equivalent of diorite.

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Andesite

Basalt a mafic extrusive rock, is the most widespread of all igneous rocks, and comprises more than 90% of all volcanic rocks. Because of its relatively low silica content, basalt lava has a comparatively low viscosity, and forms thin flows that can travel long distances. It is also found as intrusive dikes and sills. Many moon rocks brought back by Apollo astronauts are of basaltic composition. Basalt is the volcanic equivalent of gabbro.

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Basalt

Diorite is an intrusive rock intermediate in composition between gabbro and granite. It is produced in volcanic arcs, and in mountain building where it can occur in large volumes as batholiths in the roots of mountains (e.g. Scotland, Norway). Because it is commonly speckled black and white, it is often referred to as "salt and pepper" rock. Diorite is the plutonic equivalent of andesite. Gaz

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Diorite

Gabbro is a dense, mafic intrusive rock. It generally occurs as batholiths and laccoliths and is often found along mid-ocean ridges or in ancient mountains composed of compressed and uplifted oceanic crust. Gabbro is the plutonic equivalent of basalt.

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Gabbro

Granite is a felsic, relatively light coloured intrusive rock. It comprises some of the oldest known rocks on Earth, and is the most abundant basement rock underlying the relatively thin sedimentary rock cover of the continents. Granite is produced in volcanic arcs, and more commonly in mountain building resulting from the collision of two continental masses. The earliest continental masses were products of the accumulation of volcanic arcs, and this is why granite lies in the cores of all of the continents. Granite is the plutonic equivalent of rhyolite.

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Granite

Rhyolite is a felsic extrusive rock. Due to the high silica content, rhyolite lava is very viscous. It flows slowly, like tooth paste squeezed out of a tube, and tends to pile up and form lava domes. If rhyolite magma is gas rich it can erupt explosively, forming a frothy solidified magma called pumice (a very lightweight, light-coloured, vesicular form of rhyolite) along with ash deposits, and / or ignimbrite. In certain situations extremely porous rhyolite lava flows may develop. The extreme porosity of such flows allows degassing and subsequent collapse of the flow, forming obsidian (dark coloured volcanic glass). Rhyolite is the volcanic equivalent of granite.

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Rhyolite

Rhyolite is a felsic extrusive rock. Due to the high silica content, rhyolite lava is very viscous. It flows slowly, like tooth paste squeezed out of a tube, and tends to pile up and form lava domes. If rhyolite magma is gas rich it can erupt explosively, forming a frothy solidified magma called pumice (a very lightweight, light-coloured, vesicular form of rhyolite) along with ash deposits, and / or ignimbrite. In certain situations extremely porous rhyolite lava flows may develop. The extreme porosity of such flows allows degassing and subsequent collapse of the flow, forming obsidian (dark coloured volcanic glass). Rhyolite is the volcanic equivalent of granite.

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Obsidian

Rhyolite is a felsic extrusive rock. Due to the high silica content, rhyolite lava is very viscous. It flows slowly, like tooth paste squeezed out of a tube, and tends to pile up and form lava domes. If rhyolite magma is gas rich it can erupt explosively, forming a frothy solidified magma called pumice (a very lightweight, light-coloured, vesicular form of rhyolite) along with ash deposits, and / or ignimbrite. In certain situations extremely porous rhyolite lava flows may develop. The extreme porosity of such flows allows degassing and subsequent collapse of the flow, forming obsidian (dark coloured volcanic glass). Rhyolite is the volcanic equivalent of granite.

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Pumice

Mudstone is an extremely fine-grained sedimentary rock consisting of a mixture of clay and silt-sized particles. Terms such as claystone and siltstone are often used in place of mudstone, although these refer to rocks whose grain size falls within much narrower ranges and under close examination these are often technically mudstones. Shale is often used to describe mudstones which are hard and fissile (break along bedding planes). Marl is often used to describe carbonate-rich soft mudstones.

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Mudstone

Sandstone is a sedimentary rock formed from cemented sand-sized clasts. The cement that binds the clasts can vary from clay minerals to calcite, silica or iron oxides. Sandstone can be further divided according to:Clast size, Sorting - a sandstone comprising a mixture of clast sizes is poorly sorted, while one comprising mostly clasts of the same size is well sorted

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Sandstone

Conglomerate is a sedimentary rock formed from rounded gravel and boulder sized clasts cemented together in a matrix. The rounding of the clasts indicates that they have been transported some distance from their original source (e.g. by a river or glacier), or that they have resided in a high energy environment for some time (e.g. on a beach subject to wave action). The cement that binds the clasts is generally one of either calcite, silica or iron oxide. The matrix can consist solely of the cementing material, but may also contain sand and / or silt sized clasts cemented together among the coarser clasts.

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Conglomerate

Greywacke is variety of siltstone. It comprises a large percentage of the basement rock of New Zealand, and so is an important rock type throughout the country. Because it has been subjected to significant amounts of tectonic movement over a long period of time (some New Zealand greywacke is over 300 million years old), greywacke is commonly extremely deformed, fractured, and veined. Although greywacke can look similar to basalt, it differs in that it is commonly veined (with quartz being the vein mineral).

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Siltstone

Limestone is a sedimentary rock consisting of more than 50% calcium carbonate (calcite - CaCO3). There are many different types of limestone formed through a variety of processes. Limestone can be precipitated from water, secreted by marine organisms such as algae and coral or can form from the shells of dead sea creatures. As calcite is the principle mineral component of limestone, it will fizz in dilute hydrochloric acid.

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Limestone

Gneiss is a high grade metamorphic rock, meaning that it has been subjected to higher temperatures and pressures than schist. It is formed by the metamorphosis of granite, or sedimentary rock. Gneiss displays distinct foliation, representing alternating layers composed of different minerals. Gneiss is typically associated with major mountain building episodes. During these episodes, sedimentary or felsic igneous rocks are subjected to great pressures and temperatures generated by great depth of burial, proximity to igneous intrusions and the tectonic forces generated during such episodes. Gneisses from western Greenland comprise the oldest crustal rocks known (more than 3.5 billion years old). Gneiss is an old German word meaning bright or sparkling.

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Gneiss

Marble is a metamorphic rock formed when limestone is exposed to high temperatures and pressures. Marble forms under such conditions because the calcite forming the limestone recrystallises forming a denser rock consisting of roughly equigranular calcite crystals. The variety of colours exhibited by marble are a consequence of minor amounts of impurities being incorporated with the calcite during metamorphism. While marble can appear superficially similar to quartzite, a piece of marble will be able to be scratched by a metal blade, and marble will fizz on contact with dilute hydrochloric acid.

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Marble

Schist is medium grade metamorphic rock, formed by the metamorphosis of mudstone / shale, to a higher degree than slate, i.e. it has been subjected to higher temperatures and pressures forming larger crystals. These larger crystals reflect light so that schist often has a high lustre, i.e. it is shiny. Due to the more extreme formation conditions, schist often shows complex folding patterns. There are many varieties of schist and they are named for the dominant mineral comprising the rock, e.g. mica schist, green schist (green because of high chlorite content), garnet schist etc.

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Schist

Slate is a low grade metamorphic rock generally formed by the metamorphosis of mudstone/ shale, or sometimes basalt, under relatively low pressure and temperature conditions. Slate is characterized by fine layers along which it breaks to leave smooth, flat surfaces (often referred to as "slaty cleavage“. Sometimes relict (original) bedding is visible on foliation planes. Slate will 'ring' when struck, unlike mudstone or shale which makes a dull 'thud'.Gaz

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Limes

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Coal

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