Mineralogy and Rocks: Comprehensive Study Notes (Bullet-Point Format)

LEARNING COMPETENCIES

• Identify common rock-forming minerals using their physical and chemical properties.
• Classify rocks into igneous, sedimentary, and metamorphic.
• Identify the minerals important to society.
• Describe how ore minerals are found, mined, and processed for human use.

MINERALS: DEFINITION AND CORE IDEAS

• Mineral: a natural inorganic solid with a definite chemical composition and a specific crystal structure; found in the Earth’s crust; not derived from living things; minerals are the building blocks of rocks.
• Mineralogy: the study of minerals, their structure, characteristics, and uses; an earth science focused on chemistry, crystal structure, and physical properties; includes how minerals are formed and destroyed.

CHARACTERISTICS OF MINERALS

A mineral must have all of these five characteristics:

• 1) Naturally-occurring
• 2) Inorganic processes
• 3) Solid
• 4) Definite chemical composition
• 5) Ordered internal structure (crystal structure)

1) Naturally-occurring

• Minerals are formed by natural processes; materials formed in laboratories are not minerals.
• In some cases, fossils are replaced by inorganic materials through mineralization, making them mineral-like in composition.

2) Inorganic Processes

• Minerals do not contain organic compounds produced by life processes.
• Bones, shells, teeth, etc., are not minerals because they are formed by living processes.
• Fossils, if fully mineralized, can be considered minerals due to inorganic replacement of tissues.

3) Solid

• A mineral has a definite shape and volume; it does not flow like a liquid or spread like a gas.
• A mineral should be stable at room temperature (i.e., solid under standard conditions).

4) Definite Chemical Composition

• Most minerals are chemical compounds of two or more elements.
• Examples:
  • Halite: $ext{NaCl}$
  • Graphite (an element form of carbon): $ext{C}$

5) Ordered Internal Structure

• Minerals have a regular, repeating arrangement of atoms called the crystal structure.
• Determining crystallinity can require methods such as X-ray diffraction.

Mineraloids

• Mineraloids pass most criteria but lack a crystalline internal structure.
• Examples: volcanic glass, opal.
• They are typically naturally-occurring, inorganic, solid with definite composition but without ordered internal structure.

PHYSICAL PROPERTIES OF MINERALS

• 1) Luster
• 2) Hardness
• 3) Streak
• 4) Cleavage
• 5) Specific gravity
• 6) Color
• 7) Crystal Form
• 8) Transparency (Diaphaneity)

1) Luster

• The appearance of light reflected from a mineral’s surface.
• Indicates whether a mineral looks shiny or dull; metal-like or glass-like.
• Major types: Metallic Luster and Non-metallic Luster.
• Metallic luster resembles polished metal and can tarnish (e.g., pyrite may look like metal).

2) Hardness

• A measure of a mineral’s resistance to scratching.
• Mohs scale of hardness is a relative scale from 1 to 10, using common materials and standard minerals as references.
• Mohs hardness values:
  • 10: Diamond
  • 9: Corundum
  • 8: Topaz
  • 7: Quartz
  • 6: Orthoclase
  • 5: Apatite
  • 4: Fluorite
  • 3: Calcite
  • 2: Gypsum
  • 1: Talc
• Demonstrated with common objects (e.g., fingernail ~2.5, copper penny ~3.5, steel nail ~6.5, glass plate ~5.5, masonry drill bit ~8.5).
• Temperature notes: not required here, but hardness is an intrinsic property used for identification and classification.

3) Streak

• The color of the mineral in its powdered form.
• Useful for identifying minerals, especially when surface color is unreliable.
• Testing uses a streak plate (unpolished white porcelain tile).

4) Cleavage

• The tendency of a mineral to break along definite smooth planes.
• Cleavage occurs along planes of weakness in the crystal structure.
• Some minerals have cleavage in one, two, or three directions; others show poor or no cleavage.
• Examples:
  • One direction: Muscovite
  • Two directions: Feldspar
  • Three directions: Halite
  • Two directions: Calcite (in two directions but not orthogonal)

5) Specific Gravity

• The ratio of a mineral’s weight to the weight of an equal volume of water.
• Heavier minerals have higher specific gravity.
• Typical average SG for minerals is around $SG \,\approx\, 2.7$.

6) Color

• The color is the most obvious feature but often the least reliable for identification because minerals occur in multiple colors due to impurities or trace elements.
• Examples: quartz appears colorless or various colored varieties (milky, smoky, amethyst, citrine, rose quartz).

7) Crystal Form

• External shape of a mineral reflecting its internal atomic arrangement.
• Crystals are solid, homogeneous, and can form in various sizes.
• In nature, well-formed crystals with perfect faces are rare due to space and rate of growth.
• Crystals form from cooling molten material or precipitation from solutions.

8) Transparency (Diaphaneity)

• Diaphaneity describes a mineral’s ability to transmit light.
• Crystals may be transparent, translucent, or opaque depending on thickness and composition.
• Gemstones are often valued for clarity and transparency.

OTHERS: IMPORTANT INTERPRETATIONS

• Quartz and other minerals may occur in several forms or varieties (e.g., Quartz varieties: colorless, milky, smoky, amethyst, citrine, rose).
• Color alone is not a reliable diagnostic property due to impurities and lighting effects.

PETROLOGY: STUDY OF ROCKS

• PetroLOGY: study of rocks, their composition, distribution, and structure.
• It is a branch of geology focusing on occurrence, origin, physiochemical conditions, and geologic processes that form and modify rocks.

ROCKS: DEFINITIONS AND TYPES

• Rocks: naturally-occurring aggregates of minerals and mineraloids (e.g., fossils, glass).
• Role: essential in understanding the Earth's structure and history.
• Three main rock types:
  • Igneous Rocks
  • Sedimentary Rocks
  • Metamorphic Rocks

IGNEOUS ROCKS

• Formation: produced by cooling of magma or lava.
• Etymology: Igneous derives from the Latin word ignis meaning fire.

Magma vs Lava

• Magma: molten rock beneath the surface; contains molten rock, suspended crystals, and gas bubbles; temperature range $600^{\circ}\mathrm{C} \le T \le 1300^{\circ}\mathrm{C}$
• Lava: molten rock on the surface; contains molten rock and suspended solids; temperature range $700^{\circ}\mathrm{C} \le T \le 1200^{\circ}\mathrm{C}$

How igneous rocks solidify

• Solidified in three primary ways:
  • 1) Below the surface from slow-cooling magma (intrusive/plutonic rocks).
  • 2) On the surface from fast-c cooling lava (extrusive/volcanic rocks).
  • 3) On the surface from the consolidation of particles erupted by explosive volcanic activity (pyroclastic deposits).

Igneous Rock Examples

• Basalt, Pumice, Obsidian, Rhyolite, Scoria, Dacite, Granite, Gabbro, Diabase, Diorite, Pegmatite, Peridotite

SEDIMENTARY ROCKS

• Formation: accumulated on the Earth's surface through deposition from weathering and erosion and from organic materials.
• Key processes: weathering, erosion, transport, deposition, burial, compaction, cementation.

Types of Sedimentary Rocks

• Clastic (detrital): formed from accumulation of clasts (broken rocks and shells); examples include Breccia, Sandstone, Shale; coarse-grained clasts are typically > $2 \mathrm{mm}$ in diameter; clasts can be rounded (Conglomerate) or angular (Breccia).
• Chemical: formed when dissolved minerals precipitate from a solution; example: Halite (NaCl).
• Organic: formed from accumulation of plant or animal debris; example: Coal; Coal formation stages:
  • Peat
  • Lignite (soft brown coal)
  • Bituminous coal
  • Anthracite (hard coal)
  • These stages reflect increasing burial and metamorphic intensity in swamp environments with compaction and time.

Sedimentary Rock Examples (comprehensive list)

• Breccia, Caliche, Chalk, Chert, Coal, Conglomerate, Diatomite, Limestone, Sandstone, Shale, Dolomite, Siltstone, Rock Salt, Gypsum, Ironstone, Coquina

METAMORPHIC ROCKS

• Definition: rocks formed from the exposure of existing sedimentary or igneous rocks to high pressure, high temperature, or both, deep within the Earth's surface.
• Metamorphism results in changes in mineralogy, texture, and sometimes chemical composition without melting.

Metamorphic Grade and Examples

• Progressive metamorphism can be seen in rock transformations:
  • Limestone → Marble
  • Shale → Slate
  • Granite → Gneiss
• Common metamorphic rocks/examples: Marble, Anthracite (also considered a metamorphic product of coal), Gneiss, Hornfels, Mariposite, Novaculite, Quartzite, Phyllite

Types of Metamorphism

• Regional metamorphism: involves metamorphism over large geographic areas; the most widespread and common type; associated with mountain-building and large-scale tectonic processes.
• Contact metamorphism: localized metamorphism caused by heat from nearby magma; changes are driven primarily by heat with relatively limited pressure changes.
• Zones and indicators mentioned:
  • Zone of burial metamorphism
  • Blueschist and eclogite metamorphism
  • Contact metamorphism near magma chambers
  • Temperature around roughly a few hundred degrees Celsius (e.g., 400–600+ °C in illustrative diagrams)

THE ROCK CYCLE

• Concept: rocks are constantly transformed, generated, and destroyed through a continuous cycle called the rock cycle.
• Major transitions:
  • Weathering of existing rocks produces sediments.
  • Sedimentary rocks can be buried and subjected to heat and pressure to become metamorphic rocks.
  • Metamorphic rocks can melt to form magma, which can rise and crystallize to form igneous rocks.
  • Igneous rocks can also be broken down by weathering, re-entering the cycle as sediments.
• Diagrammatic sequence (as described): Weathering → Igneous Rocks → Sedimentary Rocks → Metamorphic Rocks → Heat and Pressure → Melting to form Lava/Magma → New Igneous Rocks

CONNECTIONS AND REAL-WORLD RELEVANCE

• Mineralogy is foundational for identifying minerals using physical and chemical properties, which is critical in mining, material science, and geology.
• Understanding rock types helps interpret Earth history, resource distribution (ores, fuel, building materials), and environmental impacts of mining and construction.
• The concept of ore minerals and their processing ties directly to how raw materials for electronics (e.g., cellphones) are located, extracted, and refined.
• The rock cycle explains why certain rocks are more common in specific landscapes and how tectonics, climate, and biology influence the Earth's surface over geologic time.

SUMMARY OF KEY NUMBERS AND DEFINITIONS (Quick Reference)

• Chemical formula examples: $ext{NaCl}$ for Halite; $ext{SiO}_2$ for Quartz; graphitic carbon is simply $ext{C}$.
• Mohs hardness scale: from 1 (Talc) to 10 (Diamond):
  • 10: Diamond; 9: Corundum; 8: Topaz; 7: Quartz; 6: Orthoclase; 5: Apatite; 4: Fluorite; 3: Calcite; 2: Gypsum; 1: Talc
• Specific gravity typical range for common minerals is around $SG \approx 2.7$ (dimensionless).
• Temperature ranges for magma vs lava solidification: magma cooling at depth: $600^{\circ}\mathrm{C} \le T \le 1300^{\circ}\mathrm{C}$; lava cooling at surface: $700^{\circ}\mathrm{C} \le T \le 1200^{\circ}\mathrm{C}$
• Clastic sediment grain size threshold: coarse grains generally > $2 \mathrm{mm}$ in diameter.