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Difficulty: MediumRock Types, Formation, and Economic Importance

A geologist examines a dense, crystalline rock specimen composed of recrystallized calcite grains formed when pre-existing limestone was subjected to high temperatures from a nearby magmatic intrusion. Which geological process formed this rock, and what is its major economic application?

  1. Thermal metamorphism forming marble, which is widely utilized as a decorative architectural and sculpting stone.Answer
  2. B
    Chemical weathering forming chalk, which is extracted primarily for agricultural lime production.
  3. C
    Mass movement down a slope forming scree, which is harvested for railway ballast construction.
  4. D
    Rapid extrusive cooling forming basalt, which is crushed for road construction aggregates.

Answer

Thermal metamorphism forming marble, which is widely utilized as a decorative architectural and sculpting stone.
When limestone is subjected to severe heat from nearby magma, thermal (contact) metamorphism occurs, causing calcite crystals to grow and interlock into dense marble. Economically, marble is prized for decorative building facades, flooring, and sculpture.

Step-by-Step Solution

1
Identify the parent rock and geological environment described.
Limestone (calcite-rich) exposed to intense heat from nearby magma bodies undergoes thermal (contact) metamorphism.
Magmatic heat drives mineral recrystallization without strong directional pressure.
2
Determine the resulting metamorphic rock type.
Recrystallization of calcite minerals converts limestone into non-foliated marble.
Calcite grains interlocking during thermal alteration create marble's characteristic compact texture.
3
Identify the primary economic importance of the resulting rock.
Marble takes a high polish and possesses great aesthetic value, making it ideal for monument sculpting and decorative building facades.
Physical strength, polishability, and visual appeal drive commercial quarrying for construction and art.

Key Concept

Thermal metamorphism of limestone to marble and its economic applications
Estimated Time:1m 15s
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Topics

Rock Types, Formation, and Economic Importance

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