Korean, Edit

Chapter 10. Mineralogy

Recommended Article : 【Earth Science】 Table of Contents for Earth Science


1. Definition

2. Structure

3. Classification

4. Properties

5. Formation



1. Definition

⑴ Basic units of matter that compose the Earth’s crust

Definition 1. Naturally or naturally occurring inorganic compounds or aggregates

① Exception: Coal

② Synthetic diamonds are not minerals

Definition 2. Solid at room temperature

① Exception: Mercury

Definition 3. Chemical composition remains constant or varies within a specific range

① Solid solutions vary within a limited range

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

Definition 5. Inorganic substances

① Exception: Petroleum, coral

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)

Law 1. Euler’s Law: F + S = E + 2

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

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