Chapter 11. Petrology
Recommended article : 【Earth Science】 Earth Science Table of Contents
5. Subterranean Mining and Subsurface Resources
1. Properties of Rocks
⑴ Surface Area
① Method 1. Divide into several parts and assume each as a cube, cone, or frustum of a cone for calculation.
② Method 2. If the structure has a shell, separate the shell and measure the area by spreading them on a plane.
③ Method 3. Apply metal powder to the surface, then measure the surface area based on weight changes.
④ Method 4. Image processing system.
⑵ Volume
① Method 1. Archimedes’ principle, water displacement method : Archimedes’ principle
○ V : Volume of the object (m³)
○ Wa : Weight of the object in air (N)
○ Ww : Weight of the object in water (N)
○ γw : Specific weight of water (9810 N/m³)
② Method 2. Air comparison pycnometer : Utilizing Boyle’s law
Figure. 1. Structure of a constant volume gas pycnometer
⑶ Sphericity : A scale indicating how much a rock has been eroded
① Definition 1. A scale indicating how closely the projected area matches a circle
○ R : Sphericity
○ Ap : Projected area when naturally laid on a plane (m²)
○ Ac : Area of the smallest circumscribed circle (m²)
○ L : Maximum length of the object (m)
② Definition 2. Average of the curvature radius of particle edges divided by the maximum radius of the inscribed sphere for the particles
③ Volcanic rocks and metamorphic rocks have similar sizes, but metamorphic rocks are superior in terms of sphericity.
⑷ Sphericity : A scale indicating how round a rock is
① Definition 1. Ratio of the diameter of a sphere with the same volume as the object to the diameter of the smallest circumscribed sphere
○ S : Sphericity
○ L : Length of the object (m), i.e., in the longitudinal direction
○ W : Width (m), i.e., in the direction perpendicular to the longitudinal direction
○ T : Thickness (m), i.e., height perpendicular to the plane formed by length and width
② Definition 2. Represented by (1/6) Dp Sp instead of the volume of the circumscribed sphere
③ Definition 3. Wadell’s definition : Ratio of the surface area of a sphere with the same volume as the rock to the surface area of the rock
⑸ Classification
① Definition : Degree of uniformity in particle size
② Example : Grain size distribution in sedimentary materials
Figure. 2. Grain size distribution in sedimentary materials
○ Beach gravel : Most favorable classification. Composed only of gravel.
○ Alluvial gravel : Poor classification. Composed of gravel and sand.
○ Argillaceous silt : Poor classification. Composed of gravel, sand, silt, and clay.
○ Eolian sand : Favorable classification due to transportation by wind. Composed of sand and silt.
○ Loess : Intermediate classification. Composed of sand, silt, and clay.
○ Glacial till : Poor classification.
○ Volcanic ash : Locally poor classification.
○ Particle size decreases with longer transport distance in rivers, leading to increased classification and weathering resistance.
⑹ Porosity
① Definition
○ P : Porosity
○ DB : Bulk density or matrix density (kg/m³)
○ DT : True density or particle density (kg/m³)
② (Distinction) Effective porosity : Ratio of void area to total area
2. Igneous Rocks
⑴ Definition : Rocks formed from molten materials within the Earth’s interior
⑵ Magma
Figure. 3. Process of magma formation
⑶ Lava : Classified based on SiO2 content
① Tholeiitic lava : Primary volcanic rocks, ocean floor formation ( ∵ Low viscosity), major lava flows
② Alkali lava : Stratovolcano formation
③ Alkaline lava : Cinder cone volcano, lava dome formation ( ∵ High viscosity)
④ Pāhoehoe lava has a smooth and wrinkled surface compared to ʻaʻā lava.
⑷ Types of Igneous Rocks
Figure. 4. Types of igneous rocks
① Volcanic rocks, Plutonic rocks, Hypabyssal rocks
○ Volcanic rocks : Formed at the Earth’s surface. Faster cooling → smaller particle size. Porphyritic, glassy. Basalt, etc.
○ Plutonic rocks : Formed in the deep subsurface of the Earth. Slower cooling → larger particle size. Phaneritic. Granite, etc.
○ Hypabyssal rocks : Formed in between volcanic and plutonic rocks. Diorite, etc.
② As SiO2, Na2O, CaO content increases; FeO, MgO content decreases
○ Indicates more crystal formation, hence lower crystallization temperature
○ Rich in oxygen, therefore acidic rocks
○ Increased intermolecular forces lead to higher viscosity
○ Greater oxygen emission leads to more volcanic gas and increased explosive behavior
○ More volcanic gas leads to a smaller proportion of magma
③ Memory Tip: Ultramafic, Mafic, Intermediate, Felsic
⑸ Major Igneous Minerals
① Quartz
② Feldspar
③ Mica
④ Amphibole
⑤ Pyroxene
⑥ Olivine
⑹ Formation
① Formation of joints
○ Jointing : Fractures in rocks resulting from weathering
○ Sheet jointing (e.g., Jeju Island sheet jointing)
○ 1st. Lava erupts to the surface
○ 2nd. Jointing formation : Magma rapidly cools, creating fractures in the rock
○ Columnar jointing (e.g., Insu Peak in Bukhansan)
○ 1st. Plutonic rock forms deep underground
○ 2nd. Plutonic rock is exposed at the surface: Due to lower atmospheric pressure than underground pressure, exposed plutonic rock expands
○ 3rd. Jointing formation : Fractures form due to the expansion of plutonic rock
○ 4th. Weathering mostly occurs in joint crevices, leading to exfoliation : Characterized by thin, layered separation
⑺ Igneous Rock Regions
① Jeju Island : Sheet jointing is rapidly solidified basalt
② Dokdo : Volcanic island formed by solidified lava erupted from the seafloor
③ Ulleungdo
④ Bukhansan
⑤ Seoraksan : Composed of granite
3. Sedimentary Rocks
⑴ Definition : Rocks formed from consolidated sedimentary materials
⑵ Step 1. Erosion
① Narrow definition : Formation of sedimentary materials from parent rocks
② Broad definition : Includes chemical erosion (dissolution)
○ Example : Involves karst processes that create karst topography
③ More energetic motion of transporting media leads to more active erosion
④ Chemical erosion is active in tropical environments
⑶ Step 2. Transportation : Determines particle size
① Definition : Process in which sedimentary materials move
② Factor 1. Water
③ Factor 2. Wind
④ Factor 3. Particle weight : Heavy particles settle rather than being transported
⑷ Step 3. Deposition : Formation of sedimentary rocks after accumulation of sedimentary materials
① Diagenesis : Process where sedimentary materials bind together
○ Involves heat, chemical reactions, therefore weak metamorphism
○ Classified as cementation and compaction processes
② 3-1. Cementation
○ Process that adheres sediment particles together
○ Water, especially groundwater, plays a crucial role
○ Calcium carbonate, silica, iron oxides act as binding agents
③ 3-2. Compaction : Also known as compression
○ Lower layers of sediment are compressed by overlying sediment, reducing pore space between sediments
⑸ Types of Sedimentary Rocks
① Type 1. Clastic sedimentary rocks
○ Definition : Fragments of original rocks, most sedimentary materials belong to this category
○ Wentworth Scale
Φ = -log2 Particle diameter (mm)
○ Features
○ Particle edges erode due to weathering and erosion
○ Interparticle spaces contain cementing material
○ Bedding
○ Examples
○ Shale : Diameter ＜ 0.001 mm, Φ ＞ 10 ( ∵ Clay)
○ Siltstone : Diameter = 0.001 ~ 0.1 mm, Φ = 3 ~ 10 ( ∵ Silt)
○ Sandstone : Diameter = 0.1 ~ 1 mm, Φ = 0 ~ 3 ( ∵ Sand)
○ Conglomerate : Diameter = 1 mm, Φ ＜ 0 ( ∵ Granule)
○ Tuff : Rock formed by volcanic debris deposition
② Type 2. Clastic Sedimentary Rock
○ Definition : Excludes sediments from weathering and erosion, except for terrigenous sediments. Includes organic clastic rocks, etc.
○ 2-1. Chemical Clastic Rocks
○ Limestone (CaCO3) : Chemically and organically formed clastic rock. Precipitated from solution.
○ Halite (NaCl) : Formed by evaporation.
○ Gypsum (CaSiO4·2H2O) : Formed by evaporation.
○ 2-2. Organic Clastic Rocks : Fossils can be found.
○ Coal : Plant remains deposited.
○ Limestone : Calcareous organisms (corals, mollusks, foraminifera) deposited.
○ Chert (siliceous rock) : Derived from harmful secretions of deposited organisms.
③ Type 3. Mixed Clastic Rock
○ Definition : Possesses characteristics of clastic and non-clastic sedimentary rocks.
○ Example 1. Limestone shale
○ Example 2. Carbonaceous shale
○ Example 3. Tuff shale, breccia
⑹ Classification of Sedimentary Strata
① Continental Strata
○ Aeolian Strata : Materials transported by wind and deposited on continents (e.g., Loess layer, Loam layer)
○ Glacial Strata : Deposits of glacial transport (e.g., lateral moraines, terminal moraines, ground moraines)
○ Lacustrine Strata : Sediments within lakes (e.g., clay, sand, gravel, silt)
○ Fluvial Strata : Deposits mainly in river catchments (e.g., floodplains, alluvial fans, deltas, terraces)
② Marine Strata
○ Coastal Strata : Deposits formed by tides and currents
○ Littoral Strata : Sediments deposited up to 200 m from the coast, including continental shelf deposits
○ Sublittoral Strata : Sediments in depths of 200 to 1,500 m on the continental slope
○ Abyssal Strata : Deep-sea deposits in depths exceeding 1,500 m
⑹ Sedimentary Rock Regions
① Geokpo-ri Coast
② Mt. Mai : Terrain primarily composed of metamorphic rock
4. Metamorphic Rock
⑴ Definition : Rock formed through the alteration of pre-existing rocks
⑵ Type 1. Contact Metamorphic Rock
① Definition : Rocks altered due to contact with high-temperature magma
② Characteristics
○ Recrystallization : Process where minerals dissolve and reform as larger particles
○ Dense and hard texture
○ Porphyroblastic texture : Found in igneous and metamorphic rocks. Large grains interlock closely.
○ Hornfelsic texture : Found in hornfels. Fine-grained and hard texture.
③ Types : Remember using the mnemonic “sa-gyu-seok-dae-sae-hon” (quartzite, marble, hornfels, metapelite)
○ Quartzite : Formed from sandstone. Porphyroblastic texture.
○ Marble : Formed from limestone. Porphyroblastic texture.
○ Hornfels : Formed from shale or limestone.
○ Metapelite : Formed from clay-rich rocks.
⑶ Type 2. Regional Metamorphic Rock
① Definition : Rocks formed over a large area due to heat and pressure
② Characteristics : Foliation
○ Foliation is categorized into slate, phyllite, and more based on intensity
○ Slate : Thin, parallel layers of colorless and colored minerals
○ Phyllite : Thick layers of colorless and colored minerals
③ Types
○ Amphibolite : Formed from basalt
○ Metamorphic Grade : Shale → Slate (schist) → Phyllite → Schist → Gneiss
○ Schist : Exhibits foliation
○ Gneiss : Exhibits gneissic banding
○ Gneiss has larger particle sizes compared to schist
⑷ (Reference) Type 3. Dynamic Metamorphic Rock
① Definition : Rocks formed due to increased pressure accompanying tectonic movements
⑸ (Reference) Type 4. Shock Metamorphic Rock
① Definition : Rocks formed in localized, high-pressure environments caused by meteorite impact
⑹ Metamorphic Rock Regions
① Baekryeong Island : Composed of metamorphic rock, with developed cliffs and caves due to erosion
② Jirisan (Mount Jiri)
5. Subterranean Mining and Underground Resources
⑴ Subterranean Mining
① Formation of Ore Deposits
○ Vein Differentiation Mining : Hydrothermal, geothermal, contact
○ Precipitation Mining : Supergene, residual, sedimentary veins due to groundwater, organic precipitation
○ Dynamic Metamorphism Mining
② Residual Mining
○ Supergene Mining : Deposition from transported weathered materials
○ Examples: gold, platinum, sphalerite, cassiterite
○ Residual Mining : Rocks chemically weathered into products
○ Examples: magnetite, hematite, siderite, kaolinite, bauxite, monazite
○ Hematite : Forms from oxidized iron
○ Bauxite : Formed from weathered laterite, source of aluminum
○ Aluminum refining uses bauxite as a source
○ Sedimentary Mining : Precipitates from evaporating seawater
○ Examples: halite, limestone, chert, manganese nodules, oolitic iron ores
○ Limestone : Raw material for cement
○ Manganese Nodule
○ Mainly composed of manganese
○ Contains nickel, copper, iron, and other metals
○ Occurs mainly in deep-sea sediments
○ Requires refining due to its metallic content
③ Mineral Resources of the Seabed (examples: platinum, iron, tungsten, copper, lead, zinc, gold, silver)
○ Magmatic Deposit : Formation of dense minerals during magma cooling
○ Pegmatite Deposit : Formation from volatile-rich magma invading surrounding rocks during late magma cooling
○ Hydrothermal Deposit : Formation due to interaction of vapor and volatile constituents between magma and rocks
○ Hydrothermal Vein Deposit : Remaining hot water solution forms minerals after magma cooling
④ Metamorphic Mining
○ Regional Metamorphic Mining
○ Formation due to wide-scale regional metamorphism and heated water
○ Examples: graphite, serpentine, asbestos (non-metallic)
○ Remember “black serpentine” for mnemonic
○ Contact Metasomatic Mining
○ Formation at the contact between limestone and intrusive rocks
○ Example: iron, copper, tungsten, lead, zinc
○ Sometimes categorized as hydrothermal mining
⑵ Marine Resources
① Biological Resources
○ Mostly edible
○ Increased reproduction → marine ranching
② Mineral Resources
○ Salt, manganese nodules, etc.
③ Energy Resources
○ Fossil Fuels
○ Coal, petroleum, natural gas, etc.
○ Abundant in continental shelves
○ Contribute to global warming
○ Gas Hydrates
○ Methane + ice
○ Found in deep-sea and permafrost. Present near Dokdo.
○ High-pressure, low-temperature environment
○ Non-renewable resource due to long formation time
○ Emission of greenhouse gases when used
○ Tidal Power Generation
○ Current Power Generation
○ Wave Power Generation
○ Ocean Thermal Energy Conversion
Input : 2016-06-22 20:53
Updated : 2021-02-20 12:23