Sedimentary Rocks Quiz

Formation and Types of Sedimentary Rocks

• Sedimentary rocks form through the packing together of sediments.
• Pre-existing rocks must first be transformed into sediment to become sedimentary rocks.
• Sediments are generated through weathering (breaking down rock and soil) and erosion (movement of particles by wind or water).

Classification of Sedimentary Rocks

• Sedimentary rocks are classified based on rock type, texture, and structure.
• Three primary types of sedimentary rocks are:
  • Clastic: Formed from pre-existing rocks pressed together.
  • Chemical: Result from dissolution and precipitation of minerals, often involving evaporated solutions.
  • Organic: Composed of compacted organic matter like decomposed plants.

Characteristics of Sediments

• Clastic sedimentary rocks can be categorized by the size of their sediment:
  • Boulder size (e.g., conglomerate)
  • Cobble, pebble, or granule size (e.g., breccia)
  • Sand size (e.g., sandstone, graywacke)
  • Finer sizes (e.g., siltstone, clay)

Texture and Structure of Rocks

• Coarse texture indicates large, visible particles in the rock.
• Fine texture suggests the absence of visible sediments.
• Crystalline rocks have a defined crystal structure, whereas resinous rocks resemble resin.
• A glassy structure appears shiny and smooth.

Formation of Metamorphic Rocks

• Metamorphic rocks develop from existing rocks subjected to high temperatures and pressures deep within the Earth.
• Foliation refers to the layering seen in some metamorphic rocks; they cleave along these layers.
• Parent rocks are the original rocks before metamorphism occurs, such as:
  • Schist: Parent rock is phyllite.
  • Slate: Parent rocks include shale and mudstone.
  • Quartzite: Parent rock is sandstone.

Basic Concepts of Rocks and the Rock Cycle

• Rocks are aggregates of mineral crystals and can consist of rock fragments, volcanic glass, and organic materials.
• The continental crust is primarily granite, composed of quartz, biotite, and feldspar.
• The oceanic crust consists mainly of basalt, composed of pyroxene and olivine.
• Most rocks are made up of common minerals such as quartz, feldspar, mica, or calcite.

Rock Cycle Overview

• The rock cycle illustrates the slow transformation of rocks over time through various geological processes.
• Igneous rocks form from the cooling of magma or lava.
• Metamorphic rocks are altered by heat and pressure.
• Sedimentary rocks form from cemented sediments.

Identification and Composition

• Rocks can be identified based on grain size, shape, chemical composition, and texture.
• Grains are fragments that compose the rock.
• Igneous rocks can be classified as:
  • Mafic (Basaltic): Dense, dark, high in iron and magnesium.
  • Felsic: Less dense, lighter in color, high in aluminum and silicon.
  • Andesitic: Intermediate composition between basaltic and granitic rocks.

Rock Examples and Classifications

• Common examples:
  • Igneous Rocks: Basalt, obsidian.
  • Metamorphic Rocks: Gneiss, marble.
  • Sedimentary Rocks: Conglomerate, limestone.
• Foliated rocks show curvy, thin crystal lines, while non-foliated rocks lack such lines.

Geological Processes

• Compaction: Pressure from overlaying sediments compresses grains and expels pore water.
• Cementation: Pore spaces are filled with ions that precipitate from water, forming solid bonds.

Additional Key Facts

• Approximately 75% of rocks on the Earth's surface are sedimentary.
• Organic sedimentary rocks are formed from once-living materials.