Understanding Sedimentary and Metamorphic Rocks: Formation, Uses, and Processes

Posted on Sep 20, 2025 in Geology

Sedimentary Rocks: Formation and Composition

Detrital Sedimentary Rocks:

  • Conglomerates: Composed of various sized rock fragments.
  • Sandstones: Primarily composed of sand-sized grains.
  • Clays: Fine-grained sediments.

Organogenic Detrital Sedimentary Rocks:

  • Carbon-Rich: Formed from vegetable matter.
  • Oil Shale: Contains a mixture of hydrocarbons and organic remains.
  • Planktonic: Diatomite, phosphorite.

Chemical Sedimentary Rocks:

  • Phosphate Rocks: Formed by phosphate precipitation.
  • Siliceous Rocks: Quartz, silex.
  • Carbonate Rocks: Magnesium and carbon-rich.
  • Ferruginous Rocks: Iron and aluminum-rich (bauxite).
  • Evaporitic Rocks: Steaming and gypsum precipitation, silvina.

Uses of Rocks

Industrial Uses:

  • Aluminum industry.
  • Cement production (using clay).
  • Concrete construction.
  • Energy production (coal and oil).

Sedimentary Rock Features

  • Stratification: Layers (strata) with a roof and wall.
  • Structure: Geometric arrangement of the rock.
  • Texture: Internal system of components.
  • Composition: Rock composition based on formation conditions.

Diagenesis: Transformation of Sediments

Diagenesis is the set of physical, chemical, and biological changes that sedimentary deposits undergo.

  • Compaction: Pressure increases, volume decreases.
  • Cementation: Union of particles through a cement.
  • Chemical Changes: Dissolution, ion exchange, oxidation, reduction, recrystallization, and replacement.

Soil Profile Horizons

  • Horizon A: Washing of salts into lower horizons.
  • Horizon B: Precipitation of salts from upper horizons.
  • Horizon C: Weathering of bedrock.

Edafogenesis: Soil Formation

Edafogenesis is influenced by:

  • Bedrock.
  • Weather.
  • Climate.
  • Living organisms.
  • Topography.
  • Human action.

Sedimentation, Transport, and Erosion

  • Sedimentation: Settlement of materials through deposition, decanting, and precipitation.
  • Transport: Transfer of materials from place to place by wind, rivers, sea water, ice, glaciers, and gravity.
  • Erosion: Mobilization of materials by water, ice, or air.

Metamorphic Rocks: Uses and Textures

Uses: Marble for carving and embellishing monuments; slates for roofing.

Metamorphic Rock Textures

  • Granoblastic: No leafy minerals (marble, quartzite, cornubianite).
  • Slaty: Very small minerals (slate).
  • Schistose: Larger shale.
  • Cataclastic: Irregular fragments.
  • Gneissic: Banding (gneiss).
  • Migmatite: Grainy texture, metamorphic remnants (migmatite).

Metamorphism Grades

  • Low Grade: Low pressure and temperature changes.
  • High Grade: High pressure and temperature, magmatic.

Metamorphism Factors

Metamorphism involves changes without melting, influenced by:

  • Temperature (T).
  • Pressure (P).
  • Presence of magmatic fluids.

Magmatic Rocks

  • Plutonic: Orthoclase syenite, granite, granodiorite, quartz diorite, diorite, gabbro (plagioclase peridotites, olivines).
  • Volcanic: Rhyolite, trauita, basalts (basalt = gabbro, diorite, andesite).
  • Filonian: Diabase (basalts).

Magma: Molten rock. Types: basalt, andesite, and granite.

Magmatic Processes

  • Gravitational Differentiation: Solid and liquid phases separate.
  • Magmatic Assimilation: Magma melts and assimilates surrounding parts.
  • Mixing: Original magma rock.

Weathering: Rock Breakdown

Weathering is the set of changes that materials undergo in contact with the atmosphere.

  • Physical Weathering: Tectonic forces, gelifraction, bioclastia, termoclastia.
  • Chemical Weathering: Dissolution, oxidation-reduction, carbonation, hydrolysis, hydration.

Sedimentary Environments

  • Delta: Sedimentary environment formed by materials deposited in rivers and estuaries.
  • Seafloor: Small quantities of marine sediment.
  • Estuaries: Produced by rivers entering seas, eroding glaciers.
  • River: Detrital sediments forming terraces.

Oilfield Alteration

Alteration due to water infiltration and surface weathering.

Deposition Factors

  • Mechanical: Wind, water.
  • Chemical: Salinity, temperature.
  • Biochemical: Action of organisms.

Magmatic Rock Structures

  • Batholith: Large mass of plutonic rock, magma chamber.
  • Sill: Mass of magma injection.
  • Dike: Tabular masses of magma injection.
  • Pipe Structure: Magma conduit feeding a volcano.