Rocks and Igneous Rocks Summary

Definition of Rocks

• Naturally-occurring solid aggregates of minerals or non-mineral solid matter.
• Formation processes: cooling and crystallization, cementation, heating and squeezing.

Identification of Rock Types

• Composition:
  • Types of minerals present.
  • Proportions of minerals.
  • Overall bulk composition (e.g., felsic vs. mafic).
• Texture:
  • Size and shape of mineral crystals.
  • Patterns of mineral grains (rock fabric).
• Determined by origin (formation process).

Types of Igneous Rocks

• Intrusive Igneous Rocks:
  • Formed from magma cooling beneath Earth's surface.
  • Exhibit slow cooling, resulting in larger crystals.
  • Examples: granite (felsic), diorite (intermediate), gabbro (mafic).
• Extrusive Igneous Rocks:
  • Formed from magma (lava) that erupts at the surface.
  • Cool rapidly, resulting in smaller crystals.
  • Examples: rhyolite (felsic), andesite (intermediate), basalt (mafic).

Types of Intrusions

• Pluton: General term for an intrusive body of varying size.
• Batholith: Large intrusive body (>100 km²), typically deeper in crust.
• Dike (Dyke): Sheet of rock formed in a fracture within existing rock; varies in thickness and length.

Classification of Igneous Rocks

• Based on:
  • Origin: intrusive vs. extrusive.
  • Composition: mineralogy and the proportion of minerals.
  • Texture: size, shape, and arrangement of minerals.

Characteristics of Textures

• Coarse-Grained: Large crystals, indicative of slow cooling (e.g., granite).
• Fine-Grained: Small crystals or glassy texture, indicative of rapid cooling (e.g., basalt).

Summary of Igneous Rocks

• Three major types of rocks: igneous, sedimentary, metamorphic.
• Igneous rocks classified by origin (intrusive or extrusive), as well as composition and texture.