Igneous Rocks
Granite Characteristics
Igneous
Intrusive (plutonic)
Cooled slowly
Coarse-grained
light coloured
crystalline
Composed of feldspar, mica, quartz
Hard
Wicklow mountains
Connemara (pink granite)
Granite Landscape
Location of Leinster Chain
Wicklow Mountains
Part of the Leinster Mountain chain
Covers approx. 3000 Km2
Composed of very large igneous intrusions
Formed between 450 – 370 million years ago (Caledonian period)
Batholith
Magma is intruded under the earth’s crust
Doesn’t break through the surface
Cools slowly, produces granite
Existing rocks were metamorphosed to produce schists (Lugnaquilla)
Weathering exposed the granite
Basalt Characteristics
Igneous
Extrusive (volcanic)
Cooled quickly
Fine-grained
Dark grey/Black
Tiny crystals
Rich in iron oxide (feO)
Hard
Basalt Landscape
Antrim Plateau
Giant’s Causeway
Types of Lavas
Runny lavas
Runny and flow well
Spread out before cooling
Form along spreading centres (fissures)
as plates diverge
Form basalt plateaus
e.g. Iceland and Antrim
Sticky Lavas
Don’t flow well
Solidify quickly
Form where ocean and continental plates collide
Make explosive, steep volcanic cones
e.g.Taranaki
Flood Basalts
Basalt Plateaus (flood basalts)
Form when lava flows out of a fissure or fault in the earth’s crust
Typically such eruptions occur on the sea floor
Can occur on land
Lava cools quickly so crystals are small
Continued eruption results in a lava or basalt plateau
Iceland formed in this way
Iceland sits on the Mid-Atlantic Ridge Rift
A series of fissures traverse the country north to south
Deccan Traps,India
Giant’s Causeway
formed during the early Tertiary period
62 – 65 million years ago
Three lava outflows occurred
Lower, Middle and Upper Basaltic
Lulls occurred between the outflows
deep reddish brown layer (laterite)
which is rich iron and aluminium oxides
weathering of the basalt.
situated in an equatorial region
hot and humid conditions.
The famous hexagonal columns occur in the middle basalt layer
Produced from rapid cooling of basalt
Sedimentary Rocks
Limestone Characteristics
Organic/Biological sedimentary rock
Tropical seas
Fine to coarse-grained
White to grey
Fossiliferous (rich in fossils)
reacts with acid
calcium carbonate
Soft rock
Easily weathered
Limestone Landscape
The Burren – Formation
The Burren is a unique karst region in Ireland
covers approximately 360 Km2 in north Country Clare.
composed of gently dipping beds of carboniferous limestone.
formed about 350 million years ago
region was submerged beneath warm tropical waters
marine deposition occurred
dead sea creatures fell to the ocean floor.
became fossilised.
region was uplifted
began to weather rapidly.
soil cover formed however
over-cultivation during the Neolithic
exposed the area to increased weathering
result is the present day karstic landscape
Limestone Weathering
Limestone is a calcareous sedimentary rock
weathers differentially.
When rainwater falls combines with small amounts of carbon dioxide
forms a weak carbonic acid.
Through the process of carbonation,
the acid rain changes the calcium carbonate in the limestone into a soluble bicarbonate
CaCO3 + H2O + CO2 – Ca(HCO3)2
Calcium Carbonate + Carbonic Acid – Calcium bicarbonate
Limestone is also a well jointed rock
differential resistance to weathering
explains the pattern of grikes associated with Limestone Pavement
Rainfall picks out weaknesses on the surface
long shallow depressions are exploited by the rainfall as it drains from the surface
Over time these depressions develop into grikes.
Surface Limestone Landforms
Limestone Pavement
Clint
Grike
Subterranean Limestone Landforms
Continued weathering of limestone also produces underground features
Caves, caverns, Stalactites, Stalagmites, Curtains, etc.
Cycle of karst landscape development
Sandstone Characteristics
Inorganic/clastic sedimentary rock
Composed of sand
Medium to coarse-grained (0.6-2mm)
Red, yellow, grey
Granular
grains are visible
Soft-to-hard rock
Sandstone Landscape
Ridge and Valley Province, Munster
Name given to landscape of fold mountains in Munster
Series of fold mountains
380/360 mya
Ireland close to the equator
Sediments were deposited in the shallow sea to the south
Formed Old Red Sandstones of Southern Ireland
Ridge and Valley Province
350/300 mya
Carboniferous Period
Ireland beneath a warm tropical sea
Formation of Carboniferous Limestone
Covered the Old Red Sandstone
300/250 mya
African landmass (Laurentia) collided
with the Eurasian/north American landmass (Gondwana)
Old Red Sandstone in Cork-Kerry are folded
Hercynian/Amorican/Variscan orogeny
Comeragh, Knockmealdowns,
Macgillycuddy Reeks, Galtee Mountains
Ireland on the Equator
Differential erosion
Limestone was worn away
Limestone valleys floors (synclines)
Sandstones Ridges (Anticlines)
This folding had a dramatic effect on the flow of rivers
Shale Characteristics
Inorganic Sedimentary rock
Compressed mud
Fine-grained
Soft, easily spilt
Light to dark grey
Metamorphosed into slate
Metamorphic Rocks
Types of metamorphism
Thermal – by heat
Dynamic – by pressure
Regional – by heat and pressure on a large scale
Thermal Metamorphism
Mica schist
Dynamic metamorphism
Pressure along moving faults deforms rocks
Breccias are formed as rocks shatter
Deeper in the crust rocks become ductile
Rock is ground into fine particles
Mylonite forms
It is a laminated rock with lens shaped fragments
Regional metamorphism
Happens on a large scale
Colliding plates
Rocks changed by heat and pressure
Structure and chemical make up of rocks may change
Marble Characteristics
Non-foliated (not layered)metamorphic
Made from limestone
Fine to coarse-grained
Dense rock
Crystalline
white, green, black red,
Brittle
Quartzite Characteristics
Metamorphic rock
Made from sandstone
Granular
Crystaline
Very hard
Resistant to weathering
greyish
Slate Characteristics
Foliated (layered) metamorphic rock
Fine-grained
Brittle
Easily split
Permeable
grey