Earth Science: Classification of Rocks

ROCKS AND MINERALS

• Rocks are natural, solid, nonliving materials composed of one or more minerals.
• Minerals are the building blocks of rocks.

TYPES OF ROCKS

• Rocks are classified into three major types: igneous, sedimentary, and metamorphic.

IGNEOUS ROCK

• Derived from the Latin word for "fire."
• Formed from the cooling and solidification of magma.
• Crystal size depends on cooling time: slow cooling produces large crystals, rapid cooling creates small crystals.

Main Categories

• Extrusive Igneous Rocks (Volcanic)

  • Form on the Earth's surface from lava.
  • Generally have small crystals due to rapid cooling, known as aphanitic texture.

• Intrusive Igneous Rocks (Plutonic)

  • Form below the Earth's surface from magma that cools slowly.
  • Characterized by large, visible crystals, known as phaneritic texture.

TEXTURE OF IGNEOUS ROCKS

• Coarse Grained (Phaneritic)

  • Large, visible crystals; examples include granite, gabbro, and diorite.

• Fine-Grained (Aphanitic)

  • Small, invisible crystals; example includes basalt.

• Porphyritic Texture

  • Contains two different crystal sizes, with phenocrysts (larger) in a finer groundmass.

• Glassy Texture (Vitreous)

  • Non-crystalline rocks with no mineral grains, such as obsidian.

• Vesicular Texture

  • Formed by gas bubbles from rising magma, resulting in a porous appearance.

CHEMICAL COMPOSITION OF IGNEOUS ROCKS

• Felsic Rocks

  • Light-colored, high in feldspar and quartz.

• Mafic Rocks

  • Dark-colored, rich in magnesium and iron; example includes basalt.

• Andesitic (Intermediate) Rocks

  • Contain a mix of light and dark minerals like amphibole and plagioclase feldspar.

• Ultramafic Rocks

  • Composed mainly of dark minerals such as olivine.

BOWEN’S REACTION SERIES

• Describes the crystallization process of magma.
• Discontinuous Series: Minerals crystallize in steps (e.g., olivine, pyroxene).
• Continuous Series: Plagioclase minerals range from calcium-rich at high temperatures to sodium-rich at low temperatures.

SEDIMENTARY ROCKS

• Formed from the accumulation of sediments or pre-existing rocks.
• Commonly develop at or near the Earth's surface through sedimentary processes.

SEDIMENTARY PROCESSES

• Weathering: Breakdown of rocks into smaller fragments.
• Erosion: Movement of weathered materials.
• Transportation: Sediment movement via wind, water, or gravity.
• Deposition: Occurs when energy decreases, allowing sediments to settle.
• Lithification: Converts sediment into rock, primarily through compaction.

COMMON SEDIMENTARY FEATURES

• Stratification and Bedding: Layers of sediment.
• Cross Bedding: Inclined layers formed by water or wind movement.
• Graded Bedding: Layering characterized by decreasing grain size.
• Ripple Marks: Formed by flowing water over sediments.
• Mudcracks: Result from drying sediments.
• Fossils: Indicators of past life and depositional environments.

TYPES OF SEDIMENTARY ROCKS

• Clastic: Composed of grains, classified by particle size (e.g., sandstone, shale, conglomerate).
• Non-Clastic: Formed by evaporation/precipitation of minerals or lithification of organic matter (e.g., limestone, coal).

METAMORPHIC ROCKS

• Formed from existing rocks due to pressure and temperature changes during metamorphism.

Types of Metamorphism

• Contact Metamorphism

  • Involves heat and reactive fluids from nearby magma, creating non-foliated rocks.

• Regional Metamorphism

  • Occurs under high pressure and extensive deformation, typically during mountain-building events.

This quiz covers the classification of rocks, focusing on igneous rocks and their formation from magma. Learn about the characteristics and processes involved in rock formation. Ideal for Earth Science students looking to deepen their understanding of geology.