Chapter 10. Mineralogy
Recommended Article : 【Earth Science】 Table of Contents for Earth Science
1. Definition
2. Structure
4. Properties
5. Formation
1. Definition
⑴ Basic units of matter that compose the Earth’s crust
⑵ Definition 1. Naturally or naturally occurring inorganic compounds or aggregates
① Exception: Coal
② Synthetic diamonds are not minerals
⑶ Definition 2. Solid at room temperature
① Exception: Mercury
⑷ Definition 3. Chemical composition remains constant or varies within a specific range
① Solid solutions vary within a limited range
⑸ Definition 4. Possess a specific crystal structure
① Minerals of the same type have the same arrangement of internal atoms or ions
② Exception: Opal has a slightly different crystal structure based on water content
⑹ Definition 5. Inorganic substances
① Exception: Petroleum, coral
⑺ Definition 6. Each exception is considered a sub-mineral and falls under the broader definition of minerals
① Hematite and magnetite are considered minerals in the broader sense
2. Structure
⑴ Crystalline and non-crystalline
① Laue’s spot: X-ray diffraction analysis revealing internal structure of minerals
② Crystal: Molecules arranged regularly forming distinct external shapes
③ Crystalline minerals: Atoms and ions composing minerals arranged in regular patterns
○ Laue’s spot shows regular patterns
④ Non-crystalline minerals: Atoms and ions composing minerals arranged irregularly
○ Laue’s spot shows irregular patterns
⑵ Regularity of crystals
① Three elements of crystals: Faces (F), Edges (E), and Solid angles (S)
② Law 1. Euler’s Law: F + S = E + 2
③ Law 2. Law of constant angles between crystal faces
○ Crystal faces: Angles between perpendiculars dropped to adjacent crystal faces
○ Corresponding angles in the same type of mineral are always the same
○ Tools: Contact goniometer, reflection goniometer
④ 6 crystal systems: Classified based on axial lengths (axis ratio) and angles between axes
○ Isometric (Cubic) system: Cube
○ Examples: Pyrite, Halite, Quartz, Pyrrhotite, Garnet (Uvarovite), Spinel
○ Tetragonal system: Prism with a square base
○ Examples: Zircon, Copper sulfide
○ Hexagonal system
○ Examples: Corundum, Quartz, Graphite
○ Orthorhombic system: Rectangular parallelepiped
○ Examples: Andalusite, Sulfur, Topaz
○ Monoclinic system: Most common in nature
○ Examples: Gypsum, Epidote, Augite, Actinolite
○ Triclinic system
○ Examples: Albite, Microcline
⑶ Crystal growth
① Crystal growth influenced by growth environment, crystallographic orientation, etc.
② Maturity of crystals leads to euhedral, subhedral, and anhedral forms
○ All minerals have a crystal form
○ Crystals form from euhedral to subhedral to anhedral, with anhedral forms losing their distinctive structures due to lack of space
③ Crystal symmetry: Number of times the crystal repeats its original shape upon rotation
⑷ Igneous minerals
① About 30 minerals comprising actual rocks
② 7 major silicate minerals: Plagioclase > Quartz > Olivine > Pyroxene > Amphibole > Biotite > Muscovite (12%)
③ Basic structure of silicate minerals is SiO44- tetrahedron combined with (+) ions
④ Crystal structure of silicate minerals
○ Isolated structure (e.g., garnet)
○ Cleavage, weathering: Small
○ No shared oxygen
○ Si : O = 1 : 4
○ Chain structure 1. Pyroxene
○ Cleavage, weathering: Medium
○ Two shared oxygen
○ Si : O = 1 : 3
○ Chain structure 2. Amphibole
○ Cleavage, weathering: Medium
○ Two to three shared oxygen
○ Si : O = 4 : 11
○ Sheet structure (e.g., biotite)
○ Cleavage, weathering: Large
○ Three shared oxygen
○ Si : O = 2 : 5
○ Framework structure (e.g., quartz, feldspar)
○ Four shared oxygen
○ Si : O = 1 : 2
3. Classification
⑴ Silicate minerals
① Most minerals found in the Earth’s crust are silicate minerals: 92% of all minerals
② Reason: Formation of Earth resulted in such composition
○ 1st. Presence of planetesimals in the early solar system
○ 2nd. Accumulation of these formed primitive Earth
○ 3rd. Heat energy generated during formation of primitive Earth
○ 4th. Heavy elements (e.g., Fe, Ni) gathered towards Earth’s center in liquid state
○ 5th. Abundant elements on Earth are iron and silicates with low-density chemical species, i.e., silicate minerals
③ Supplement: Current geological situation
○ 8 major elements in Earth’s crust: Eight elements constitute over 99%
O > Si > Al > Fe > Ca > Na > K > Mg
○ Oxygen is abundant (mass ratio: 45.2 wt%, atomic ratio: 92 vol%)
○ Some chemical species are dispersed (e.g., Rb), some are concentrated (e.g., Zr in zircon, Ti in rutile)
○ Less abundant elements are mined from concentrated locations
○ Oxygen and silicon, relatively abundant elements, form most minerals → dominance of silicate minerals
④ Structure with four oxygen atoms surrounding a silicon atom (however, this ion configuration is highly unstable with a charge of -4)
○ Silicate minerals combine with other ‘cation’ to form various shapes
○ ‘Cation’: Excluding oxygen and silicon from the eight major elements, i.e., Al, Fe, Ca, Na, K, Mg
⑵ Classification of silicate minerals
① Classification criteria
○ Criterion 1. How silicon atoms with an unstable -4 charge are balanced (related to high-temperature and low-temperature origins)
○ Criterion 2. Color of rocks
○ Criterion 3. Continuous series and discontinuous series
○ Continuous series: Substitution of cations during crystallization
○ Discontinuous series: Crystal structure continually changes during crystallization
○ Crystallization: Mineral formation through magma
② Order of magma crystallization
Figure 1. Order of magma crystallization
A: Mafic magma, B: Andesitic magma, C: Felsic magma
○ Memorization tip: Mafic Andesitic Felsic
○ Lower SiO2 content corresponds to lower temperature
○ Higher SiO2 content corresponds to higher viscosity
○ SiO2 is a major component of glass, so it feels sticky
② High-temperature crystallization minerals: Crystallize at high temperatures, categorized into iron-magnesium silicates and non-iron-magnesium silicates
③ Iron-magnesium minerals (ferromagnesian): Iron, magnesium neutralize a charge of -4
Figure 2. Characteristics of iron-magnesium minerals
Figure 3. Structure of pyroxene and amphibole
Figure 2. Indicates overlapping of features
○ Common features
○ Colored minerals: Green, black, dark gray due to iron and magnesium
○ High density due to iron
○ Increasing number of shared oxygen between adjacent faces from Type 1 to Type 4
○ Decreasing melting point from Type 1 to Type 4
○ Type 1: Olivine group
○ Chemical formula: (Mg, Fe)2SiO4
○ Mg2+ and Fe2+ can substitute each other due to similar ionic radii
○ Structure: Independent tetrahedral structure. Independent type
○ Each silicate exists independently in the form of regular tetrahedron
○ Intercalated cations neutralize -4 charge
○ Type 2: Pyroxene group
○ Chemical formula: XYSi2O6 or (Mg, Fe)SiO3
○ Structure: Chain structure
○ Also called single chain or monoclinic chain structure
○ Rows of pyroxenes connected one by one in this structure
○ Silicate tetrahedra share oxygen on both sides
○ Intercalated cations neutralize -4 charge
○ Characteristics
○ Angle of cleavage is 90°
○ Column-shaped crystals
○ Development of two-directional cleavage : Originates from chain structure
○ Type 3: Amphibole group
○ Chemical formula: Ca2Na(Mg, Fe)4(Al, Fe, Ti)3Si6O22(OH, F)2 or Ca2Mg5(Si4O11)2(OH)2
○ Structure: Double chain
○ Also called double chain or orthorhombic chain
○ Rows of amphiboles connected two by two in this structure
○ Silicate tetrahedra share two oxygen in opposite directions
○ Intercalated cations neutralize -4 charge
○ Characteristics
○ Angle of cleavage is 120°
○ Column-shaped crystals
○ Development of two-directional cleavage : Originates from double chain structure
○ Type 4: Mica group
○ Chemical formula: K(Mg, Fe)3(OH)2AlSi3O12 or Al2Si2O3(OH)4
○ Structure: Sheet structure
○ All facts are connected to form a single plane
○ Silicate tetrahedra share three oxygen
○ Intercalated cations neutralize -4 charge
○ In essence, ion bonds are formed through oxygen-cation-oxygen connections, weaker than van der Waals forces but stronger than for true van der Waals solids like graphite
○ Slightly sensitive to forces, tending to split thinly : Graphite is an example of an application of van der Waals forces
○ Black mica is an iron-magnesium mineral, while white mica belongs to non-ferromagnesian minerals
○ Black mica is more common in granite than in basalt
○ Development of one-directional cleavage
④ Non-iron-magnesium minerals (non-ferromagnesian): Aluminum neutralizes a charge of -4, usually light-colored
○ Crystal Structure of Silicates: Tetrahedral structure in which tetrahedral silicate ions share all four oxygen atoms, forming a 3D structure.
○ Generally, the more complex the bonding of tetrahedral silicates, the more stable the structure, making it resistant to weathering.
○ Type 1: Quartz
○ Composed solely of silicon and oxygen, with all oxygen atoms shared among tetrahedral silicates.
○ Forms a crystal structure with tectosilicate framework.
○ Type 2: Feldspar Group - Plagioclase
○ Same crystal form for Ca feldspar and Na feldspar: Cations substitute for some silicon in the tetrahedral silicate structure.
○ Plagioclase can split in two directions.
○ Distinguished as Ca feldspar and Na feldspar (solid solution relationship).
○ Solid Solution: Ions from a solution infiltrate an existing crystal structure when solid is present in solution.
○ Na+ and Ca2+ can substitute for each other.
○ Composition of Ca feldspar and Na feldspar according to temperature: Ca feldspar precipitates first in initial high-temperature state.
Figure. 4. Composition of Ca feldspar and Na feldspar based on temperature
○ Andalusite is also a solid solution mineral.
⑤ Low-temperature metamorphic minerals
○ Principle
○ High-temperature minerals form faster than low-temperature minerals.
○ React vigorously with large amounts of oxygen at high temperatures.
○ Low-temperature minerals conserve oxygen and maximize sharing to form complex structures called polysomatic structures.
○ Type 1: Orthoclase - K2O·Al2O3·6SiO2
○ Also known as K feldspar.
○ Low-temperature metamorphic mineral with low cation content.
○ Unlike plagioclase, there are no metal cations substituting in low-temperature conditions, so no solid solution exists.
○ Comprises around 12% of igneous minerals.
○ Transforms into kaolinite through chemical weathering.
○ Type 2: Mica Group - Muscovite (Refer above)
○ Type 3: Quartz - SiO2, crystalline structure (framework structure)
○ Almost devoid of cations.
○ Has more covalent bonds compared to ionic bonds in other minerals.
○ Increased resistance to weathering.
○ High Mohs hardness: 7
○ Abundance of quartz in beach sand due to its resistance to weathering.
○ Tip: Minerals become more resistant to weathering as they undergo later stages.
○ Reason 1: Greater number of covalent bonds.
○ Reason 2: Decreased ionic character.
⑥ (Reference) Clay Minerals
○ Layered silicate minerals with a flaky structure.
○ Kaolinite is a clay mineral.
○ Plasticity: Absorbs water to become malleable, hardens upon drying.
⑶ Non-silicate Minerals
① Constitute about 10% of Earth’s crust.
② Classification
○ Oxides: Magnetite (Fe3O4), etc.
○ Sulfides
○ Sulfates
○ Carbonates
○ Native elements
③ Examples: Pyrite (FeS), Galena (PbS), Barite, Copper (Cu), Halite (NaCl), Gypsum, etc.
○ Barite: Most common carbonate mineral.
4. Properties
⑴ Physical Properties
① Streak: Color of the mineral when scratched or rubbed against a surface.
○ # : Surface Color - Streak Color
○ Gold: Yellow - Yellow
○ Hematite (Fe2O2): Red - Red
○ Pyrite (FeS2): Yellow - Black
○ Magnetite (Fe3O4): Black - Black
○ Quartz: Colorless - White
○ Chalcopyrite (CuFeS2): Yellow - Bluish Black
○ Goethite (Fe2O3·nH2O): Dark brown - Ocher
○ Streak color of Ca feldspar, Na feldspar, and K feldspar is the same.
② Hardness and Mohs Scale represent the relative hardness of minerals.
Table. 1. Hardness and Mohs Scale
○ Mnemonic Tip: A lively bow and a shield that’s not in good condition made a strong gold bow.
○ No. 1: Talc - Very weak due to weak van der Waals bonding.
○ Structure: Layers connected by covalent or ionic bonds within the layer.
○ Substructure 1: T-layer - Layer composed of Si-O tetrahedra, covalently bonded.
○ Substructure 2: O-layer - Layer composed of Mg-O(OH) octahedra, ionically bonded.
○ Substructure 3: Si-O-Mg bonds between T-layer and O-layer, covalently bonded.
○ Substructure 4: T-O-T layers connect through van der Waals forces.
○ Talc’s name signifies its slipperiness.
○ No. 2: Gypsum
○ It’s evident in daily life that gypsum is very soft.
○ No. 3: Calcite (carbonates)
○ Reacts with hydrochloric acid to release CO2, creating bubbles.
○ Often forms from shell material, very soft.
○ Displays double refraction.
○ Colorless, transparent, glassy luster remains.
○ Main component of limestone and dolomite.
○ No. 7: Quartz
○ Main component of sand. Low-temperature metamorphic mineral.
○ Silicon and oxygen are only connected by covalent bonds, making it very hard.
○ No. 10: Diamond
○ One type of allotrope of carbon consisting solely of carbon.
○ Forms strong covalent bonds - C-C bonds stronger than Si-O bonds.
○ Others
○ Andalusite: 6.8
③ Cleavage: Property where a mineral splits along planes.
○ Types: Gypsum, anhydrite / talc, biotite / muscovite, halite / barite / fluorite, calcite, aragonite / dolomite, feldspar
○ Memory Aid 1: Biotite has one direction of cleavage. Barite has three directions of cleavage.
○ Memory Aid 2: Biotite, muscovite, feldspar: Two directions of cleavage.
○ Graphite
○ Bonding within one plane makes it flaky.
○ Weaker van der Waals forces between layers make it split easily.
○ Layers separate easily, leading to low hardness.
④ Fracture: Property where minerals break without preferred direction.
○ Examples: Andalusite, quartz, hornblende
⑤ Specific Gravity
⑥ Optical Properties
⑵ Chemical Properties
① Reaction with Hydrochloric Acid: Rocks with -CO3 group (e.g., calcite) release CO2 when reacting with hydrochloric acid.
⑶ Optical Properties
① Color
○ Elements that impart color: Ti, V, Cr, Mn, Fe, Co, Ni, Cu
○ Violet minerals: When a colorant is the primary component.
○ Colored minerals: When a colorant is a secondary component.
○ Impurities can also impart unique colors.
○ Example: Quartz turns amethyst with added impurities.
② Streak
○ Produced from the reflection of light off a mineral’s powdered structure.
○ Example 1: Streak of hematite: Red
○ Example 2: Streak of pyrite: Black
③ Transparency
○ Transparent minerals: Light passes through when mineral is thin.
○ Opaque minerals: Even thin sections of the mineral block light. Metallic minerals, etc.
④ Luster: Differentiated into metallic luster, non-metallic luster, sub-metallic luster.
⑤ Polarization: Unique pattern seen when light passing through a mineral displays distinctive patterns.
○ Principle of Polarization
○ 1st. Minerals that are anisotropic have varying internal cohesion.
○ 2nd. Light speed varies within the mineral.
○ 3rd. Light passing through the mineral creates unique patterns.
○ 4th. Observed using polarizing microscopes.
○ Uniaxial Optics (Optical Isotropic)
○ Definition: Minerals where light speed remains constant regardless of direction.
○ Examples: Diamond, halite, spinel, garnet
○ Biaxial Optics (Optical Anisotropic)
○ Definition: Minerals where light speed varies with direction.
○ Examples: Most minerals
Figure. 5. Significance of Biaxial Optics
○ Polarizing Microscope
Figure. 6. Structure of Polarizing Microscope
○ Upper polarizer is insertable, lower analyzer is fixed.
○ Polarizer direction of upper and lower components is orthogonal.
○ N conoscopic interference figure : Upper polarizer absent. Generally, minerals appear bright.
○ Pleochroism : Observing pleochroic minerals under N conoscopic, colors and brightness change.
○ Minerals showing birefringence can appear light under crossed Nicols.
○ C conoscopic interference figure : Upper polarizer present. Generally, minerals appear dark.
○ Interference colors : Viewing optically anisotropic minerals under C conoscopic, interference patterns form due to birefringent rays.
○ Extinction : Minerals appear black under C conoscopic.
○ Complete Extinction : Under crossed Nicols, only minerals undergoing birefringence appear dark. Optical isotropic minerals exhibit complete extinction.
○ 4-fold extinction : When mineral section is rotated 360° under crossed Nicols, 4 extinction positions can be observed.
○ Reason : Related to the fact that rotating ‘+’ by 90° makes it ‘+’ again (to be updated later).
5. Formation
⑴ From Melt
⑵ From Solution
⑶ From Vapor
⑷ From Metamorphism
Input : 2016.6.22 20:54