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Difficulty: MediumRock Types, Formation, and Economic Importance

Rocks are classified based on their origin, physical characteristics, and economic utility. Which option correctly matches each rock type with its formation process and primary application?

  • BasaltFine-grained extrusive igneous rock formed by the rapid cooling of basic lava on the Earth's surface, widely crushed for road construction.
  • ChalkSoft, porous calcareous organic sedimentary rock composed of microscopic marine organisms, used in manufacturing agricultural lime and cement.
  • GneissHigh-grade foliated metamorphic rock formed under intense regional heat and pressure, exhibiting distinct light and dark mineral bands.
  • Rock SaltEvaporite chemical sedimentary rock formed by the precipitation of dissolved minerals in drying lakes or seas, utilized heavily in chemical industries.

Answer

Basalt matches fine-grained extrusive igneous rock used in road aggregate; Chalk matches soft calcareous organic sedimentary rock used for agricultural lime; Gneiss matches high-grade foliated metamorphic rock with distinct mineral bands; Rock Salt matches evaporite chemical sedimentary rock used in chemical industries.
Each rock is matched correctly to its fundamental genetic class: Basalt is an extrusive igneous rock used as road aggregate, Chalk is an organic sedimentary rock used for agricultural lime, Gneiss is a foliated metamorphic rock displaying banded minerals, and Rock Salt is a chemical evaporite sedimentary rock used in industry.

Step-by-Step Solution

1
Identify the origin and characteristics of Basalt.
Basalt is formed from rapid surface cooling of basic molten lava (extrusive igneous) and is economically valuable as road aggregate.
Extrusive volcanic rocks cool quickly, creating fine-grained crystalline textures suited for heavy construction.
2
Identify the origin and characteristics of Chalk.
Chalk forms from compressed calcium carbonate micro-organisms in shallow seas (organic sedimentary) and serves in lime/cement making.
Organically derived rocks consist of accumulated biological remains.
3
Identify the origin and characteristics of Gneiss.
Gneiss forms from intense heat and pressure altering protoliths into banded structures (foliated metamorphic).
High-grade regional metamorphism causes mineral segregation into distinct light and dark layers.
4
Identify the origin and characteristics of Rock Salt.
Rock salt forms through evaporation of saline water bodies (chemical sedimentary evaporite) and is used in industrial chemical processes.
Chemical sedimentary rocks precipitate directly out of saturated aqueous solutions.

Key Concept

Rock Classification by Formation Mode and Economic Importance
Estimated Time:1m 30s
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Topics

Rock Types, Formation, and Economic Importance

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