Download Introduction To Rock Types

Cheshire RIGS
SALTscape Lectures at The
Weaver Hall Museum, Northwich
Prof Cynthia Burek
University of Chester
Veronica Cubitt-Caddy
Cheshire RIGS
Dr Ian Drew
Manchester Metropolitan University
Cheshire RIGS
SALTscape Lecture
Rocks & Building Stone
Saturday 24th January 2015
Weaver Hall Museum
Dr Ian Drew
Division of Environmental & Geographical Sciences,
Manchester Metropolitan University
[email protected]
Elements, Minerals & Rocks
The mineral
Quartz = the elements
Silicon+Oxygen
The rock Granite = the
minerals Quartz+Feldspars+
Micas+Amphiboles
The Rock Cycle
Magma
Hawaii Volcano Observatory (DAS) - http://hvo.wr.usgs.gov/kilauea/update/archive/2003/May/main.html
Cooling & Crystallisation
Igneous Rock
Magma
Igneous Rocks
Igneous rocks are produced as molten magma from
the upper mantle rises towards the Earth’s surface,
cools and crystallises.
Classification of igneous rocks is based on:
– Mineral composition
• Felsic – Intermediate – Mafic – Ultramafic
– Texture (crystal size)
• Coarse – Medium – Fine – Glassy
These characteristics reflect the elemental content of
the magma (the minerals) and it’s cooling history (the
texture).
Igneous Rock Textures
• Coarse texture
– Large Crystals
– Magma cooled &
crystallised slowly.
– Indicates cooling within
the crust – the magma
never erupted onto the
Earth's surface.
– Intrusive igneous
rocks
Granite
Gabbro
• Fine texture - Small
crystals.
– Magma cooled &
crystallised more
quickly.
– Indicates cooling on
the Earth’s surface –
typically solidified
lava flows.
– Extrusive igneous
rocks
Rhyolite
Basalt
Crystal Size (mm)
Igneous Rock Compositions
• Felsic igneous rocks
Typical Minerals:
Quartz
– Also known as acid igneous rocks. Orthoclase & Plagioclase Feldspars
Muscovite & Biotite Micas
– Generally lighter in colour.
Amphibole
– High silica content.
Granite
Rhyolite
• Mafic igneous rocks
– Also known as basic igneous rocks.
– Generally darker in colour.
– Lower silica content
Gabbro
Basalt
Typical Minerals:
Plagioclase feldspar
Amphibole
Pyroxene
Olivine
Other Types of Igneous Rock
• Tuff & Ignimbrite
– Ash rocks
1996 Mount Ruapehu, NZ
Charred logs in Taupō ignimbrite 200AD
• Obsidian / pitchstone – volcanic glasses
Cristobalite “snowflake” inclusions
There are no Natural Outcrops of Igneous rock
in Cheshire but some are used as ornamental
stones on buildings and memorials
Larvikite (“Blue Pearl) from Norway
Feldspars display a “shillar” effect
Granite from Shap in Cumbria
Distinctive pink feldspars
The Mat Hatters Tea Party - Alice in Warrington!
Granite in Northwich Town Centre
White granite
steps and
ornamental
facing stone
Porphyry setts with Black granite 'Artscape' paving
• Basalt & granite have traditionally been used
as curb stones, sets and cobbles
www.pavingexpert.com
Rock Cycle
Cooling & Crystallisation
Igneous Rock
Weathering &
Erosion
Sediment
Magma
• When a rock is exposed at the
surface of the Earth it will be
broken down by environmental
conditions.
• The breakdown can be into solid
pieces (physical weathering &
erosion) or by dissolving (chemical
weathering).
– The solid fragments are referred to
as sediments
– The dissolved materials as are
referred to solutions
Scree of weathered fragments
Physical weathering
Granite exfoliation
Chemical
weathering
http://gpc.edu/~pg
ore/geology/geo1
01/weather.htm
Dissolving of
Cleopatra’s
needle
A. Egypt after 30+
Centuries
B. NYC after 75
years
• The sediments and solutions will later form
the components of sedimentary rocks…
• Rocks created from the solid fragments of preexisting rocks are termed CLASTIC
sedimentary rocks.
• Rocks created from the dissolved rock
material (or from the remains of living
organisms) are termed NON-CLASTIC
sedimentary rocks.
• The sediments are typically transported away
from their source by water, ice or air.
• They are then deposited in layers (referred to as
beds or strata) in environments such as oceans,
lakes or deserts (referred to as sedimentary
basins).
• The processes by which the loose sediments are
then converted to sedimentary rocks are termed
lithification.
– Drying
– Compaction by pressure of material accumulating
above
– Cementation by minerals precipitated from solution
• The subdivision of clastic sedimentary rocks is based on the
size of sediment grains they contain.
Palaeoenvironmental Reconstruction
• Geological detective work – the size and shape of
the clastic grains are clues to the type of
environment in which the rocks were created.
• This is often supported by palaeontological
evidence – fossils preserved in the sedimentary
rocks – more details in a later SaltScape lecture.
Green River Fossil Fish, Colorado
http://geology.com/articles/green-river-fossils/
Course Clastic Sedimentary Rocks
Grains over 2mm in diameter cemented by a finer matrix.
• Conglomerate
– Large rounded grains set in finer
matrix.
– Environments of Deposition ?
www.gpc.edu/
Chester Pebble beds at Little Barrow
Medium Clastic Sedimentary Rocks
• Grain size 0.06mm to 2mm
• Sandstone (finer)
• Gritstone (coarser)
• Strength is determined by the
cement bond – friability.
• Origins?
– Beach, river, delta or desert (red
sandstones)
– Grain size provides details of
ancient flow conditions
Chatsworth
Grit Quarry at
Tegg’s Nose
Country Park,
Macclesfield
Identifying Desert Sandstones
Active dune
200 million year old dune
Near Alderley Edge
The red colour represents iron oxidation associated with weathering in
desert conditions
The diagonal “cross bedding” represents the movement of windblown
sand dunes
Cheshire Triassic Red Sandstone Outcrops & Architecture
Closest use of local sandstone??
www.geograph.org.uk/photo/2927564
Cheshire Quarries
Helsby Hill
Bridge Quarry, Kerridge
www.bridgequarry.co.uk
But not all sandstone buildings in Cheshire are red…
Crewe Municipal Buildings
Yorkstone Paving Slabs
There are also gritstones
quarried in the far
Northwest of Cheshire
which were used for local
buildings
Chatsworth Grit
Roaches Grit
Fine Clastic Sedimentary Rocks
• Grain size less than 0.06mm
–
–
–
–
Siltstones
Mudstones
Clays
Shales (thinly bedded – fissile)
• Usually originate as deep &/or
still water deposits.
– Ocean floor
– Lake
Tarporley Siltstone,
Alderly Edge
Clay rock showing mud cracks
Graptolitic shale
The fine grained
clay rocks are a
raw material in
the manufacture
of bricks
Non-Clastic Sedimentary Rocks
• Hydrogenic = precipitated from water
5 million year old
evaporites, Sicily
Limestone cave
speleothems
• Biogenic = derived from organic materials
Coal
Shelly
limestone
Winsford Rock Salt Mine
• Britain’s oldest working mine – since 1844
www.winsfordrocksaltmine.co.uk
Limestones
• Wide variety of Calcium carbonate (CaCO3) rocks
• Often associated with tropical environments.
• Examples of limestone types Biogenic / Hydrogenic
– Bio-clastic limestone = shell fragments.
– Reef limestones = Whole fossils.
– Oolitic = spherical grains composed of precipitated
concentric layers.
Oolites
– Chalk = Microfossil ooze.
– Tufa = Hydrogenic speleothems.
– Marl = Calcareous mudstone
Limestone gallery
Oolitic
Biogenic
Chalk
Speleothem
• Fossiliferous limestones
– Crinoidal limestones
Coral
limestones
www.ukfossils.co.uk
• Shelly Limestones
Oyster bed Lower Jurassic, found at
Barmston
http://www.fortunecity.com/greenfield/
ecolodge/60/erratics.htm
Corraline Limestone, Gozo
Portland Limestone from Dorset
Rock Cycle
Cooling & Crystallisation
Magma
Igneous Rock
Weathering &
Erosion
Sediment
Weathering &
Erosion
Lithification
Sedimentary Rock
Metamorphic Rocks
• Pre-existing rocks subsequently altered by heat
and pressure.
• Changes in mineralogy & texture
• Solid state (i.e. without melting) replacement of
minerals and reorientation of crystals
• The threshold between sedimentary diagenesis
and metamorphism is gradational.
Metamorphic Rock Types
• The important factors in determining the
nature of the rocks produced by
metamorphism are:
– The original rock type
– The amount of heat/pressure (the grade of
metamorphism)
• Main textural division into foliated (cleaved or
banded) and non-foliated (granular)
metamorphic rocks
• Marble
– Calcareous (calcium carbonate)
– Sugary texture (unpolished)
– Pure forms are white but many
ornamental examples are
streaked with colour due to
impurities.
Sir John Crew (1711) Attrib. Andries Carpentiere
St Helen, Tarporley
www.earthscienc
www.library.csi.cuny.edu eeducation.com
Marble with
serpentine streaks;
Ledmore, Assynt,
NW Scotland
www.earth.ox.ac.uk
Quartzite
– Quartz sand grains
cemented very tightly by
extensive pressure
solution
Microscopic views
www.pdac.ca
– Sandstone – rounded quartz
sand grains cemented with
haematite
– Quartzite – straight sided grains
penetrating into each other
www.library.csi.cuny.edu
• Slate
– Fine grained.
– Dark.
– Distinctive cleavage
www.tulane.edu/~sanelson/eens212/metatexture.htm
Braichmelyn Slate Quarry,
Bethesda from A55
Lion Salt Works
http://thelionsaltworks.blogspot.co.uk/
2013_12_01_archive.html
• Schist
– Highly foliated
(crenulated schistosity).
– Medium to course
grained.
– Shiny lustre due to high
mica content.
– May contain crystals of
the red mineral garnet.
www.tulane.edu/~sanelson/eens212/m
etatexture.htm
geo.stanford.edu
• Gneiss
– Course grained.
– Banded with light &
dark layers.
– Similar mineralogy to
igneous granites.
geo.stanford.edu
Rock Cycle
Cooling & Crystallisation
Magma
Igneous Rock
Weathering &
Erosion
Heat &
Pressure
Metamorphic Rock
Weathering &
Erosion
Sediment
Weathering &
Erosion
Lithification
Sedimentary Rock
Heat &
Pressure
Melting
• If heat & pressure continue to increase the
original rock material will eventually begin to
melt.
• When this melt cools it will crystallise into a
Migmatite (partial melt) or an acid igneous
rock such as granite (full melt).
Migmatite (Verde Maritaca)
As featured on the floor of the
main foyer of the Arndale
Shopping Centre in Manchester.
This Completes the Rock Cycle
Cooling & Crystallisation
Magma
Melting
Igneous Rock
Weathering &
Erosion
Heat &
Pressure
Metamorphic Rock
Weathering &
Erosion
Sediment
Weathering &
Erosion
Lithification
Sedimentary Rock
Heat &
Pressure
Follow-Up Reading
Download from: www.bgs.ac.uk/downloads/start.cfm?id=2062
Future Cheshire RIGS
SALTscape Talks
Geological conservation (2015)
Plate tectonics and continental drift (2015)
Ice Age in Cheshire (2016)
Triassic hot deserts of Cheshire (2016)
Fossils (2016)
Dinosaurs (2016)
Geological Resources (2017)
Geology of the Saltscape region (2017)
Soils (2017)
…Also guided geological walks and town trails…