ROCKS VERSUS MINERALS
1. Minerals – naturally occurring inorganic solids, which posses a definite internal structure and specific chemical composition.
2. Rocks –consist of one or more minerals.
- e.g . mineral : calcite; rock : limestone.
| ELEMENT | SYMBOL | % OF EARTH’S CRUSH |
| Oxygen | O | 49.52 |
| Silicon | Si | 25.75 |
| Aluminium | Al | 7.51 |
| Iron | Fe | 4.70 |
| Calcium | Ca | 3.39 |
| Sodium | Na | 2.64 |
| Potassium | K | 2.40 |
| Magnesium | Mg | 1.94 |
| Total % | 97.85 | |
| % of other element | 2.15 | |
Table1.1: Composition of element in earth’s crust
pink chalcedony
|
pink chalcedony |
sulphur |
|
Azurite |
Flourite |
Figure 1.1: Types of rock
Minerals
1. Minerals – naturally occurring inorganic solids, which posses a definite internal structure and specific chemical composition.
• Gold is mineral.
• Syntactic diamonds are minerals.
• Petroleum is mineral.
• Animal bone is mineral.
• Steel is mineral.
Figure 1.2: Crusher
2. Mineral group
Silicon + oxygen = silica (Quartz SiO2 is pure silica)
3. Minerals containing silica = silicates minerals (Olivine Mg2Fe2SiO4 & Orthoclase KAlSi3O8).
4. 2 subgroups of silicate mineral:
• Ferromagnesian silicates: (dark color, > dense).
• Nonferromagnesian silicates : (light color, <>
Figure 1.3: Silicate minerals
5. Carbonate mineral , (CO3)-2 :
• Minerals calcite (CaCO3) : limestone.
• Mineral dolomite (CaMg(CO3)2).
Figure 1.4 : Carbonate minerals
6. How are minerals identified
a) Colour
• Unreliable diagnostic properties.
• E.g. – impurities of quartz give variety colour (pink, purple, milky white).
Figure 1.5 : Colour of minerals
| MINERAL | COLOUR | SG | HARDNESS | CLEAVAGES |
| Olovine | Green / Dark green | 3.5+ | 6.5 | None ( poor fracture) |
| Pyroxene (augite) | Black / Brown | 3.3 | 5.5 | 2 |
| Hornblende | Black | 3.3 | 5.5 | 2 |
| Biotite | Brown | 3 | 2.5 | 1 ( perfect) |
| Garnet | Red (variable) | 3.5+ | 7 | None |
Table 1.2: Dark-coloured mineral silicates & their
typical physical properties
| MINERAL | COLOUR | SG | HARDNESS | CLEAVAGES |
| Feldspars | White, pink, variable | 2.7 | 6 | 2 |
| Clays | White | 2.6 | 2 – 2.5 | 1 ( perfect) |
| Quartz | Colourless, white, red, variable | 2.65 | 7 | None |
| Muscovite | Colourless | 2.7 | 2.5 | 1 ( perfect ) |
Table 1.3: Light-coloured mineral silicates & their
typical physical properties
b) Cleavage
• In crystal structure of mineral, some bonds are weaker than others.
• Cleavage – tendency of mineral to cleave or break along weak bonding (when stressed) .
• Cleavage can be identified by distinctive smooth surface that are produced when the mineral is broken.
• Fracture – mineral not exhibit cleavage.
Figure 1.6 : Cleavage in minerals
Figure 1.7 : Cleavage in minerals
Figure 1.8 : Cleavage in minerals
Figure 1.9 : Cleavage in mineral biotite (mica): 1 direction
Figure 1.10 : Cleavage in mineral calcite : 3 direction
Figure 1.11 : Serpentine (Asbestos) : fibrous fracture
Figure 1.12 : Quartz: choncoidal fracture
Figure 1.13 : Bornite : irregular fracture
c) Luster
• Luster - appearance in reflected light.
• Metallic luster – minerals that have appearance in metals.
• Nonmetallic luster – glassy, dull, silky.
Figure 1.14 : Luster appearance.
d) Hardness (Mohs hardness scale)
• Measure of the resistance of a mineral to abrasion or stretching.
• Determine by rubbing the mineral to identified against another mineral of known hardness.
| HARDNESS | MINERAL | HARDNESS OF MINERAL |
| COMMON OBJECT | ||
| 10 | Diamond | |
| 9 | Corundum | |
| 8 | Topaz | |
| 7 | Quartz | |
| | | Steel File ( 6 ½ ) |
| 6 | Orthoclase | |
| | | Glass ( 5 ½ - 6 ) |
| 5 | Apatite | |
| 4 | Flourite | |
| 3 | Calcite | |
| | | Copper Penny ( 3 ) |
| | | Fingernail ( 2 ½ ) |
| 2 | Gypsum | |
| 1 | Talc | |
Table 1.4 : Mohs Hardness Scale
e) Specific gravity
• Compares the weight of a mineral to the weight of an equal volume of water.
• E.g. – 1cm3 of a mineral weights 3 times as much as 1cm3 of water; S.G. = 3.
• S.G. of pure 24 karat gold = 20.
f) Other useful minerals properties
Figure 1.15 : Various minerals properties.
MINERALOGY
Figure 1.16 :
Diamond |  Gold |
Figure 1.17 : Unstoppable
DEFINITION
1. Volcanology is the study of volcanoes, lava, magma and related to the geological phenomena. The term of volcanology is derived from the latin word, Vulcan, the Roman God of fire.
Figure 1.18 : Lava fountains (5p;10 m high) spouting from eruptive fissures during the October 1980 eruption of Krafla Volcano.
VOLCANO
1. Volcanic action is clearly related to the existence of
2. Heat is generated in the earth’s core by nuclear process.
3. It is carried up from the core to the upper layers nearer the surface by complex convection current.
4. Then heating from below causes mantle and crustal rock become soften and melt.
MAGMA
1. Molten material that is still in the earth and which has not yet been ejected to the surface.
2. The chemical composition of the magma largely determines the eruptive behavior of a volcano.
3. Magma which is composed of mantle rock has little dissolved gas.
4. This type of magma erupts as a relatively placid viscous liquid (lava), flows smoothly if sufficiently hot and freezes into a black rock called basalt.
Figure 1.19 : Exsolution surface and Fragmentation surface
1. Exsolution surface
• Occurs in the magma reservoir beneath the volcano. It separates a zone of magma containing dissolved volatiles from an overlying zone of magma containing exsolved gas bubbles.
2. Fragmentation surface
• Occurs at the top of the magma column. It separates the zone of magma containing exsolved gas from the overlying eruption column. Fragmentation of the magma is generated by rapid gas expansion and bubble explosion.
Figure 1.20 : Plate Tectonics process
1. Plate tectonics is a gradual movement of crustal plate on the surface of the earth.
2. In certain regions, 2 plates move apart creating a rift, where volcanic magma can erupt (pacific ocean,hawaiian island).
3. In other case, 2 plates crush together and raising huge mountain ranges (Himalaya of Asia, Alps of Europe).
4. Subduction – the plate being subducted gradually bends downward & plunges into the earth where it eventually encounters sufficient heat to soften & melt.
Figure 1.21 : Volcanology
PHYSIOGRAPHY BEFORE AND AFTER THE 1883 ERUPTION
The pre-eruption
Figure 1.22 : Before and after Eruption
During the eruption, Perboewatan, Danan, and the northern half of Rakata appear to have collapsed into the vacating magma chamber, thus forming a submarine caldera and destroying the northern two-thirds of the island. Eruptions since 1927 have built a new cone called Anak Krakatau ("child of
Figure 1.23 : Karakatau
History of the Earth
1. Earth – 4.5 billion years.
2. Origin of universe – 14 billion years.
3. No water / oxygen.
4. Crust due to cooling.
5. Dinasour died 65 million years ago – Luis Alvarez.
Figure 1.24 : Origin if the earth
Figure 1.25 : Nebular hypothesis
Earth structure
1. Crust (10 – 70km): divided into oceanic and continental crust. Low density. Silicon-oxygen based.
2. Mantle (2880 – 3200km) : consists of layers of dense rocks (olivine & basalt). Temperature within mantle is about 30000C, thus materials may be in the form of liquid. Silicon-oxygen + iron + magnesium. Density of uppermost peridotite – 3.3 g/cm3.
3. Core (3480 km) : Most dense. Consists of iron – nikel alloy. Average density 11g/cm3. Temperature may exceeds 40000C.
Figure 1.26 : Earth structure
4. The top layer is called the crust.
5. Oceanic crust is thinner and denser than continental crust.
6. Oceanic crust is more active than continental crust.
7. Under the crust is the rocky mantle, which is composed of silicon, oxygen, magnesium, iron, aluminum, and calcium.
8. The asthenosphere is a part of the upper mantle that exhibits plastic properties.
9. It is located below the lithosphere, between about 100 and 250 kilometers deep.
Plate Tectonics
Figure 1.27 : Tectonic Plate Boundary Types
1. Earth's outermost layer, the lithosphere, is broken into 7 large, rigid pieces called plates.
2. The place where the two plates meet is called a plate boundary.
The dynamic earth
1. The earth is a dynamic planet.
2. The earth surface today was dramatically different from 4.6 billion years ago.
3. The process of altering the earth’s surface:
• Gradation.
• Yolcanism.
• Tectonism.
4. Gradation process: erosion & deposition – slow rate.
• Agent: atmosphere, water, wind & snow.
• When rate of deposition is higher than erosion, deposits of erosion material will happened or reflects.
5. Volcanism refers to the volcanic activity.
• Source: earth internal heat (magma & lava flow).
• Create igneous & metamorphic rock, volcanic structure.
6. Tectonics: movement of earth’s crust (start 1960s) - sea floor spreading and continental drifting.
7. Plate tectonic theory – earth’s rigid at the outer shell, lithosphere is broken into several pieces (plate).
8. Plate driven (in motion) by thermal engine – result of unequal distribution of internal heat.
9. Generate earthquake, volcanic activity & mountain.
10. Types of movement:
a. Divergent boundaries: zones where plates move apart, leaving gap between them.
Figure 1.28 : Divergent Boundary
• Places where plates are pulling apart are called divergent boundaries.
• When the lithosphere is pulled apart, it typically breaks along parallel faults that tilt slightly outward from each other.
• As the plates separate along the boundary, the block between the faults cracks and drops down into the soft, plastic interior (the asthenosphere).
• The sinking of the block forms a central valley called a rift.
• Magma (liquid rock) seeps upward to fill the cracks.
• New crust is formed along the boundary.
• Earthquakes occur along the faults, and volcanoes form where the magma reaches the surface.
Figure 1.29 : 1st step in divergent process
• This is an example of a divergent plate boundary. The mid-Atlantic Ridge is an area where new sea floor is being created.
• As the rift valley expands, two continental plates have been constructed from the original one. The molten rock continues to push the crust apart creating new crust as it does.
Figure 1.30 : 2nd step in divergent process
• As the rift valley expands, water collects forming a sea.
• The Mid-Atlantic Ridge is now 2,000 metres above the adjacent sea floor, which is at a depth of about 6,000 metres below sea level.
Figure 1.31 : 3rd step in divergent process
• The sea floor continues to spread and the plates get bigger and bigger.
Figure 1.32 : Sea floor spreading
Figure 1.33 : Ocean ridges
b. Convergent boundaries: zones where plates move together, causing one to go beneath the other, as happens when oceanic crust is involved; or where plates collide, which occurs when the leading edges are made of continental crust.
Figure 1.33 : Convergent boundaries
• Places where plates crash or crunch together are called convergent boundaries.
• When two plates collide , some crust is destroyed in the impact and the plates become smaller.
• Oceanic Plate and Continental Plate.
- When a thin, dense oceanic plate collides with a relatively light, thick continental plate, the oceanic plate is forced under the continental plate.
- This phenomenon is called subduction.
• Two Oceanic Plates
- When two oceanic plates collide, one may be pushed under the other and magma from the mantle rises, forming volcanoes in the vicinity.
Figure 1.34 : Two Oceanic Plates
• Two Continental Plates
- When two continental plates collide, mountain ranges are created as the colliding crust is compressed and pushed upwards.
Figure 1.35 : Two Continental Plates
Figure 1.36 : Subduction zone
Figure 1.37 : Tectonic collision
Figure 1.38 : Tsunami
Figure 1.39 : The convergence of the Nazca and South American Plates has deformed and pushed up limestone strata to form towering peaks of the
c. Transform fault boundaries: zones where plates slide past each other, scraping & deforming as they past.
Figure 1.40 : Transform boundaries
• When two plates move sideways against each other, there is a tremendous amount of friction which makes the movement jerky.
• The plates slip, then stick as the friction and pressure build up to incredible levels.
• When the pressure is released suddenly, and the plates suddenly jerk apart, this is an earthquake.
|
| Figure 1.41 : Aerial view of the San Andreas fault slicing through the Carrizo Plain in the |
Figure 1.42 : Three types of plate boundary ; Divergent boundaries, Convergent boundaries and
Figure 1.43 : Plate boundary
Fossil Evidence in Support of the Theory
1. Eduard Suess was an Austrian geologist who first realized that there had once been a land bridge between South America, Africa,
2. He named this large land mass Gondwanaland (named after a district in
3. He based his deductions on the plant Glossopteris, which is found throughout
The ‘jigsaw puzzle’
1. On the earth’s crust are continental mass, continental shelf & ocean basin.
2. The present continents (e.g.
3. The dynamic position (floating) of the earth’s crust on the partly liquid & melting mantle, had broken the crust into several pieces & formed the presence continents.
Figure 1.44 : Gondwanaland
