Geography EYA Revision Notes [ROCKS] ©Kimberly Chia 1
Rocks!
Glossary/Definitions/Explanations:
Mineral:
A natural inorganic substance with a definite chemical composition (eg. Diamond is carbon)
Has definite physical and chemical properties
Rock:
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One of the solid materials which makes up the Earth’s crust
Normally do not have a definite chemical composition as they are made up of different minerals
There are exceptions to it, such as limestone, which is very much predominantly made of calcite or
gypsum, which is made up of calcium sulphate crystals.
When a rock forms the chemicals organize themselves into a number of different minerals
Weathering:
Decay and disintegration of rocks of the Earth’s crust by exposure to the atmosphere.
Does not involve transportation
o Hence, work of rain and wind is NOT weathering, as it involves transporting material, so it
more strictly belongs to erosion.
Mechanical weathering:
o Expansion and subsequent contraction of rocks due to changes in temperature between
night and day
o Frost action: Rainwater freezes and expands in cracks and pores of rocks.
Chemical weathering:
o Caused by temperature changes
o Dissolving by a solution of rainwater and carbon dioxide (Carbonic acid)
o Hydration (mineral combines with water to form new compound)
o Oxidization (mineral combines with oxygen to form new compound)
Erosion:
The wearing away of the land by various natural agents, the most important of which being water.
If by water, 4 major processes
o Corrasion/Abrasion: grinding against surface by materials
o Attrition: colliding together to become smaller rocks
o Solution: Dissolve in carbonic acid. (Eg. Limestone – calcium carbonate dissolves)
o Hydraulic Action: water hitting against the rocks, loosening.
Denudation:
The wearing away of the land by various natural agents:
o Sun
o Wind
o Water (Sea, moving ice, running water, rain, frost)
Combines WEATHERING and EROSION
One of two major processes responsible for changes to form the earth’s surface, the other deposition.
Lithification:
Simply put, it is “hardening”, this process forms clastic/biogenic SEDIMENTARY ROCK. Eg.
Conglomerate, Breccia
The process whereby unconsolidated rock-forming materials (sediments) are converted under
pressure into a consolidated or solid state
Precipitation:
Occurs when minerals in solution become super saturated and precipitate (remember chem!)
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Also occurs in a body of water that is evaporating:
o Evaporation decreases the amount of water without decreasing the amount of dissolved
material, making the dissolved material become oversaturated and precipitate (like forming
crystals in Chem)
Forms chemical SEDIMENTARY ROCK/evaporite minerals
o This is how limestone forms in marine environments
o Forms the pretty crystal-like gypsum!
Metamorphism:
Process whereby rocks (in a solid state) are transformed because of intense heat and pressure
Forms metamorphic rocks, duh! (:
Uplift to surface:
Rocks buried in the earth’s crust, get uplifted to the surface of the earth’s crust
o By weathering, erosion and transport
o By plate movements
Crystallization:
Cooling of molten rock to form crystals in igeneous rock!
As melted rock cools, the heat energy that allows atoms to move past one another decreases, and the
natural attraction between atoms causes them to stick together with similar atoms in an orderly
crystalline structure. (yes chem again taken off a website!)
http://www.classzone.com/books/earth_science/terc/content/investigations/es0603/es0603page05.
cfm GO CLICK IT HAS AN ANIMATION showing crystallization in igneous rocks!
Plutonic:
Another name for “intrusive igneous rock”
Plagioclase Feldspar:
A form of feldspar containing aluminosilicates of sodium and/or calcium
Found commonly in igneous rock, generally white.
Fluvial Processes:
All your river processes as explained in erosion
Strata:
Layers or series of layers of rock on the ground.
Clasts/clastic:
Clastic denotes rocks composed of broken pieces of older rocks.
Clasts are those sediments/pieces.
Igneous Rocks:
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Comes from the word ‘ignis’, which means ‘fire’ in Latin!
Formation:
o Formed from cooling and solidifying of the molten rock i.e. lava or magma
o As the rock cools and solidifies, it forms mineral crystals, which lock together to form masses
of igneous rocks. The crystals can differ in size.
Intrusive igneous rock:
o Formed by the cooling and solidification of magma inside the Earth’s crust
o Magma cools and solidifies slowly due to high temperatures inside the earth
o Slow cooling gives rise to large crystals, crystals have time to grow and develop, and thus
intrusive igneous rocks are coarse-grained.
Extrusive igneous rock:
o Formed by cooling and solidification of lava on the earth’ surface
Geography EYA Revision Notes [ROCKS] ©Kimberly Chia 3
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Lava cools and solidifies much more quickly due to lower temperatures on the earth’s
surface
o Rapid cooling gives rise to much smaller mineral crystals as crystals have little time to grow
and develop, and thus extrusive igneous rocks are fine-grained.
Characteristics:
o Crystalline appearance
o Not in layers
o Do not have fossils
o Hard and strong
Examples of COARSE-GRAINED EXTRUSIVE IGNEOUS ROCK! :
o Granite:
 Made of quartz, alkali feldspar and mica (the black specks)
 COLOUR: Mostly white, grey, pink red, mottled combination of these colours
 GRAIN SIZE: Coarse to very coarse
 STRUCTURE: Can be banded, aligned according to flow of the granitic magma
(magma that cools into granite), generally homologus
 Used to make tombstones at times
 THE BELOW IS HOW GRANITE LOOKS LIKE (:
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Gabbro:
 COLOUR: White, shiny appearance, White grains present, crystals present
 GRAIN SIZE: Medium
 TEXTURE: Relatively smooth/rough also can
 STRUCTURE: Crystalline appearance
 Gabbro is low in silica and has no quartz, no alkali feldspar as well.
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Examples of FINE-GRAINED IGNEOUS ROCK:
o Rhyolite
 Rhyolite is typically dark and has a glassy groundmass.
 COLOUR: Grey/Dark Grey, White/Brown Grains Present
 GRAIN SIZE: Fine
 TEXTURE: Smooth
 STRUCTURE: Crystalline appearance
 Plutonic version of rhyolite is granite, having almost the same chemical composition
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Basalt
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Basalt is fine-grained so that the individual minerals are not visible.
Coarse-grained, plutonic (another word for intrusive igneous rock) version of basalt
is gabbro!
COLOUR: Black or dark grey, may be mottled black or white
GRAIN SIZE: Medium to fine
STRUCTURE: Often vesicular (having air pockets) and amygdaloidal (having other
minerals in the vesicles)
Minerals include pyroxene, plagioclase feldspar and olivine.
Geography EYA Revision Notes [ROCKS] ©Kimberly Chia 5
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Obsidian
 Produced when lava rich in silica (acidic lava) is extruded out of a volcano, and cools
rapidly without crystal growth.
 Lava flow is highly viscous (slow)
 Has a nice glassy appearance
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Pumice
 Formed when frothy lava with gases trapped in it is violently ejected out of a
volcano, and cooled rapidly.
 The cooled lava forms holes within it, left behind by the gas bubbles.
 Pumice is easily crushed and used for abrasive grit or soil amendments.
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Sedimentary Rocks:
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Comes from the word ‘sedd’ meaning SETTLE DOWN :D
Are formed from the deposition and accumulation of materials on the land surface or the sea and
compacted into layers of rock strata.
Characteristics
o Most have layered appearance
o Can find fossils!
o Crystalline appearance if chemically formed.
Can be Mechanically-formed:
o Contain rock particles (eg. Pebbles, cobbles and sand)
o Formed from compression and cementation of sediments. (Lithification)
o Hardening of layers of rock particles, which are pressed and stuck together.
Can be organically-formed:
o From compression and cementation of remains of plants and animals (fossils)
Can be chemically-formed:
o Refer to PRECIPITATION in glossary
o Crystalline appearance due to crystallization of minerals.
o Water has evaporated from solutions which contain minerals (crystallization of minerals)
Types of MECHANICALLY-FORMED Sedimentary rocks:
o Breccia
 Formed mainly by mass movement of rock materials eg. Avalanche, mudflow, and
then deposited.
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Conglomerate
 Formed by rock particles, which have been eroded and rounded through fluvial
processes before it is deposited.
 The space between the clasts is generally filled with smaller particles and/or a
chemical cement that binds the rock together.
 COLOUR: Various colours
 GRAIN SIZE: Medium to coarse
 TEXTURE: Very rough
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Structure: Many different rock particles stuck together, no layering.
Geography EYA Revision Notes [ROCKS] ©Kimberly Chia 7
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Sandstone
 Made up mainly of sand-size (1/16 to 2 millimeter diameter) weathering debris.
 COLOUR: Beige/brown, fine grains of darker reds, brown
 GRAIN SIZE: Fine
 TEXTURE: Granular, relatively rough.
 STRUCTURE: Layering present.
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Shale
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Made of hardened mud.
COLOUR: Black, grey, brown, red, dark green, BLUE?!?!
TEXTURE: Fine, smooth, not gritty
STRUCTURE: Finely bedded and splits into layers, fossils are common.
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Types of ORGANICALLY-FORMED Sedimentary rocks:
o Coal:
 From partially decomposed swamp forests.
 COAL IS UGLY SO NO PICTURE.
o Limestone
 Limestone is a sedimentary rock composed primarily of calcium carbonate (CaCO 3)
in the form of the mineral calcite.
 It most commonly forms in clear, warm, shallow marine waters. It is usually an
organic sedimentary rock that forms from the accumulation of shell, coral, algal and
fecal debris.
 COLOUR: White, grey, cream, yellow when pure, black when impure.
 TEXTURE: Highly variable, from fine-grained to coarsely crystalline & of sugary (Y)
appearance! (:
 STRUCTURE: Wide variety of fossils, criss-crossed by calcite and mineralized veins.
 MINERAL COMPOSITION: Mainly calcities.
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Types of CHEMICALLY-FORMED Sedimentary rocks:
o Gypsum (crystalline rocks)
 Formed from accumulation of calcium sulphate crystals
 THERE IS PRETTY GYPSUM GO FIND THEM YOURSELF :P :D
Geography EYA Revision Notes [ROCKS] ©Kimberly Chia 9
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Limestone (Tufa)
 A porous limestone that forms from the precipitation of calcium carbonate, often at
a hot spring or along the shoreline of a lake where waters are saturated with
calcium carbonate.
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Metamorphic Rocks:
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Formation:
o Metamorphic rocks are formed when existing igneous, sedimentary or metamorphic rocks
in their solid state are changed from their original state by great heat or pressure.
o The chemical composition and physical structure of the existing rocks are altered.
o In cases of intense metamorphism, bedding planes and fossils in the original rocks can be
destroyed. ):
Different types of metamorphism
o Regional metamorphism:
 Squeezed and heated by intense mountain building forces when plates converge
o Contact metamorphism:
 Heated by an intrusion of hot magma.
 Rocks that come into contact with hot magma melt and solidify again.
o Pressure metamorphism
 Altered under high pressure associated with earth movements WHOAA
 When rocks undergo such great pressure such as folding they are usually
rearranged into thin wavy bands.
Characteristics:
o Crystalline appearance
 Under heat and pressure, the minerals of the original rocks recrystallize, forming
large crystals in coarse-grained rocks.
o Banded structure (i.e. Layering/Foliation!)
 High pressure causes the minerals of the original rock to rearrange into bands and
layers. Pretty!
o Hard and strong!
Types of FOLIATED rocks (GO Through PRESSURE METAMORPHISM):
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Slate
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Low-pressure metamorphism of shale.
Schist
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Formed from high-pressure metamorphism of shale
COLOUR: brownish black, have individual mica flakes
GRAIN SIZE: Irregular
STRUCTURE: Banded
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GNEISS <3 cos it’s so nice!
 Formed from Granite.
 COLOUR: Black, grey, shiny crystals
 GRAIN SIZE: Coarse
 TEXTURE: Rough
 STRUCTURE: Wavy banding, mica has rearranged itself :D
Geography EYA Revision Notes [ROCKS] ©Kimberly Chia
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Types of Non-Foliated Rocks:
o Marble (Think Taj Mahal :D )
 Formed from Limestone
 COLOUR: Typically white, either uniform or blotched, banded or veined in differing
shades
 GRAIN SIZE: Medium to coarse-grained
 STRUCTURE: Commonly massive but may also have layering or banding. :D
 MINERALS: Calcite is major constituent
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Quartzite
 Metamorphism of SANDSTONEEE :D
 COLOUR: Grey with white shiny crystals
 GRAIN SIZE: Fine to medium
 TEXTURE: relatively rough.
 STRUCTURE: Crystalline appearance
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PERCENTAGE OF ROCKS:
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In earth’s crust:
o 95% Igneous Rocks:
 All of them intrusive igneous rocks like to hide in the earth’s crust, and they form
there in the Earth’s crust :D
o 5% Sedimentary Rocks
o VERY LITTLE METAMORPHIC ROCKS OH SO SAD D:
On the Earth’s Surface
o 25% igneous rocks
 Igneous rocks erode more slowly than sedimentary rocks, so it takes longer for it to
be uplifted to surface.
o 75% Sedimentary rocks:
 Sedimentary rocks form near the surface where sediments are deposited.
ROCK CYCLE:
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Go study yourself! Not providing diagram hehehe
The rock cycle describes how the Earth’s materials are cycled and recycled over geologic time.
On the Earth’s surface, rocks weather into sediment.
Within the crust, heat and pressure transform sediment to rock that is eventually exposed on the
surface.
SINGAPORE GEOGLOGY:
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Central Region
o Igneous Rocks
o Bukit Timah Granite
o Pulau Ubin – Granite
o Gombak Norite – Gabbro
Western Region
o Sedimentary Rocks
o Jurong Formation, Labrador Park – Sandstone/Conglomerate
Eastern Region and Parts of the West and North
o Deposition of Sand and Gravel Deposits – Alluvium
o Kallang Formation in the Southeast
Northeastern island
o Pulau Tekong (Metamorphic Rocks)
o Sajahat Formation - Quartzite
USES OF ROCKS
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Building and road-making materials:
o Building stones: Sandstone, Limestone, Granite, Conglomerate, schist, gneiss
o Ornamental stone: Granite, Marble
Geography EYA Revision Notes [ROCKS] ©Kimberly Chia
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o Roofing/Flooring: Slate
o Tiles/Bricks: clay
o Concrete: Clay + powdered limestone cement + sand + gravel or crushed stone.
o Plaster/plasterboard: Gypsum
Industrial raw materials
o Ceramic material: Kaolin for CHINAWARE :D
o Fertilizers: Limestone
Energy:
o Fossil Fuel: Coal
Gems and precious metals
o Found in rocks! Diamond, ruby etc.
SPACE FOR ADDITIONAL NOTES: I.E. DRAW YOUR ROCK CYCLE HERE:
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