Earth and Life Science Lesson 2

Earth’s Crust Composition

• The Earth’s crust consists of minerals and rocks.
• Minerals are individual crystals, while rocks are combinations of various minerals.

Rocks Overview

• Rocks are naturally occurring materials made up of minerals.
• Classified into three main types: Igneous, Metamorphic, and Sedimentary.
• The rock cycle illustrates how different types of rocks transform through geological processes.

Igneous Rocks

• Formed from solidified magma or lava; the term originates from the Latin “ignis,” meaning fire.
• Result from volcanic activity, with magma cooling and solidifying over time.
• Major elements in igneous rocks include Si (Silicon), O (Oxygen), Al (Aluminum), Ca (Calcium), Na (Sodium), K (Potassium), Mg (Magnesium), and Fe (Iron).

Crystallization

• Defined as the formation and growth of a crystalline solid from molten rock.
• Can occur underground or on the surface following a volcanic eruption.

Types of Igneous Rocks by Origin

• Extrusive Igneous Rocks (Volcanic Rocks): Formed when molten rocks solidify at the Earth's surface.
• Intrusive Igneous Rocks (Plutonic Rocks): Formed from magma cooling at greater depths within the Earth.

Types of Igneous Rocks by Texture

• Coarse-Grained: Crystals are visible to the naked eye, typically intrusive igneous rocks.
• Medium-Grained: Crystals can only be seen with a hand lens.
• Fine-Grained: Crystals are microscopic; requires a microscope for observation.