Rocks and Minerals Overview

Rocks

• Earth’s solid rock extends to a depth of 2,900 kilometers where it transitions into the liquid outer core.
• Rocks are natural solid aggregates of one or more minerals, bonded together chemically.
• Geologists classify rocks into three categories: igneous, sedimentary, and metamorphic.
• Petrology is the scientific study of rocks.

Igneous Rocks

• Formed from the hardening and crystallization of magma deep within the Earth.
• Two types of igneous rocks:
  • Extrusive/Volcanic: Formed from lava at Earth’s surface; characterized by fine-grained crystals.
  • Intrusive/Plutonic: Formed from magma cooling slowly underground; features large, coarse-grained crystals.
• Igneous rocks are classified based on:
  • Composition:
    • Felsic: Light-colored, contains feldspar and silicates.
    • Mafic: Dark-colored, rich in magnesium and iron.
    • Intermediate: Between mafic and felsic.
    • Ultramafic: Very dark in color.
  • Texture:
    • Aphanitic: Fine-grained.
    • Phaneritic: Coarse-grained.
    • Porphyritic: Contains both large and small crystals.
    • Glassy: Non-ordered solid, formed from rapid cooling.
    • Pyroclastic: Composed of ejected volcanic fragments.

Metamorphic Rocks

• Formed from pre-existing rocks (igneous, sedimentary, or metamorphic) through metamorphism.
• Typically found deep within the Earth or at tectonic plate boundaries.
• Two types of metamorphism:
  • Regional Metamorphism: Caused by pressure and temperature changes over large crustal regions, often associated with convergent plate boundaries.
  • Contact Metamorphism: Occurs due to heat from nearby magma, not pressure-related, resulting in non-foliated rocks.

Classification of Metamorphic Rocks

• Texture: Size and arrangement of mineral grains.
• Foliation: Planar arrangement of mineral grains.
  • Foliated: Banding or layering present (e.g., mica).
  • Non-foliated: Few minerals, no banding.

Sedimentary Rocks

• Provide insights into Earth’s past surface conditions.
• Formed from the accumulation of sediments (sand, shells, pebbles) that harden over time due to compaction.
• Three types of sedimentary rocks:
  • Clastic: Formed from accumulated clasts; examples include conglomerate and sandstone.
  • Chemical: Formed from precipitated minerals from solutions; example: halite.
  • Organic: Formed from the accumulation of biological debris; example: coal.

Minerals

• Building blocks of rocks defined by specific criteria:
  • Naturally Occurring: Formed through natural processes of Earth.
  • Inorganic: Not produced by biological processes.
  • Homogeneous Solid: Has a definite volume and rigid shape.
  • Definite Chemical Composition: Can be represented by a chemical formula.
  • Orderly Crystalline Structure: Atoms arranged in a repetitive, orderly pattern.

Properties of Minerals

• Color: Can vary based on surface conditions.
• Streak: Color of the powdered form of a mineral.
• Hardness: Resistance to scratching.
• Cleavage: Ability to break along specific planes.
• Crystalline Structure: Describes the internal arrangement of atoms.