Minerals and Rocks: Properties, Types, and Uses

Posted on Feb 1, 2025 in Geology

Minerals: Definition and Properties

Minerals are defined by four characteristics:

  • Solid – You cannot pass through them.
  • Composition – Each mineral has a specific chemical composition.
  • Natural Origin – They occur naturally.
  • Crystal Structure – Atoms are arranged regularly in three dimensions.

Formation of Minerals

  • Precipitation: Substances are sedimented.
  • Solidification of Magma
  • Recrystallization: Existing minerals re-crystallize when cooled.
  • Sublimation: Gas transitions directly to solid (e.g., sulfur).

Each mineral has a series of physical properties that depend on its chemical composition and structure.

Properties of Minerals

  1. Density: Mass/Volume
  2. Hardness: Resistance to being scratched (low, medium, high)
  3. Color: The wavelength of light that a mineral reflects.
  4. Luster: The reflection of light on the mineral.
  5. Cleavage: A mineral’s tendency to break along certain planes.
  6. Diaphaneity: Ability to transmit light (opaque, translucent, transparent).
  7. Fluorescence: Ability to emit light when exposed to certain wavelengths.

Uses of Minerals

  • Mining: Deposits are areas of high mineral concentration.
  • Mineral Ores: Valuable minerals found within gangue, forming veins.
  • Industrial Uses: Metals and nonmetals.
  • Jewelry: Based on color, luster, hardness, and transparency.
  • Gemstones: Ruby, sapphire, emerald, and diamond.
  • Semiprecious Stones: Other valuable minerals.
  • Native Minerals: Composed of a single element.

Coal, anthracite, lignite, graphite, peat, and coal are not named after an element.

Rocks: Types and Formation

Rocks are solid materials composed of several naturally occurring minerals.

Classification by Origin

  • Exogenous: Formed outside the Earth’s crust (sedimentary).
  • Endogenous: Formed within the Earth’s crust (magmatic/igneous and metamorphic).

Sedimentary Rocks

Formed through erosion, transportation, and sedimentation by external geological agents.

Diagenesis: The process of forming sedimentary rocks from sediments.

  • Compaction: Sediments are compressed.
  • Cementation: Dissolved substances (silica and CO3) act as natural cement.

Types of Sedimentary Rocks

  • Detrital: Formed from fragments of other rocks (e.g., clays).
  • Non-Detrital: Formed from the precipitation of dissolved minerals (e.g., limestone).

Materials dissolved in water form salts. Fossilized remains of living organisms can also be found in sedimentary rocks.

Igneous Rocks

Formed by the cooling and solidification of magma.

  • Volcanic: Magma cools and solidifies on the surface.
  • Plutonic: Magma cools and solidifies slowly within the Earth’s crust.

Metamorphic Rocks

Formed by a change in the structure of pre-existing rocks due to metamorphism.

Types of Metamorphism

  • Thermal: Caused by a decrease in temperature near magma.
  • Dynamothermal (Regional): Caused by increased temperature and pressure, often at tectonic plate edges.

Types of Metamorphic Rocks

  1. Slate: Formed from clay, with a layered structure.
  2. Marble: Formed from limestone, very resistant, and used in construction.

Uses of Rocks

  1. Construction: Brick, tile, clay, marble.
  2. Decoration: Marble, plaster.

Exploitation of Mineral Resources: Risks

  • Health: Exposure to toxins can endanger miners’ lives.
  • Environment: Extraction, transportation, processing, and use of minerals have environmental impacts.