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Metamorphic rock, cleavage; igneous rock significance

Short answer

Metamorphic rock forms from pre-existing rocks changed by heat, pressure, and fluids, classified as contact, regional, or dynamic, and as foliated or non-foliated. Its structures include foliated (slaty cleavage, schistosity) and non-foliated (massive, granulose). Igneous rocks like granite are strong and durable, used for foundations and aggregate, but joints and weathering must be assessed.

Define metamorphic rock and its types. Explain the structure of metamorphic rock. Give the significance of igneous rocks in civil engineering activities.

Metamorphic rock and its types

Metamorphic rock is a rock formed from pre-existing igneous, sedimentary or metamorphic rock by change in texture, structure and mineral composition in the solid state under high temperature, pressure and chemically active fluids. Metamorphism is this process.

Types by cause:

  1. Contact (thermal) metamorphic rocks - heat from nearby magma (hornfels, marble, quartzite).
  2. Regional (dynamothermal) metamorphic rocks - heat and pressure over a wide area during mountain building (slate, phyllite, schist, gneiss).
  3. Dynamic (cataclastic) metamorphic rocks - mainly pressure along faults (mylonite, fault breccia).

By texture: foliated (slate, schist, gneiss) and non-foliated (marble, quartzite).

Structure of metamorphic rocks

  • Foliated: slaty cleavage (slate), phyllitic (phyllite), schistose (schist), gneissose banding (gneiss).
  • Non-foliated: massive, granulose structure (marble, quartzite), hornfels.
  • Cataclastic and augen structures near shear zones.

Significance of igneous rocks in civil engineering

  • Strong and durable: granite, basalt and gabbro are used for foundations, piers, dams and retaining walls.
  • Crushed igneous rock is a main source of concrete aggregate, road metal and railway ballast.
  • Dimension stones: polished granite for flooring, facing and kerbs.
  • Being massive, non-porous and without bedding, they are suitable sites for dams and tunnels, but joints, weathering and sheeting must be examined.
  • Dykes and sills may form weak zones or barriers to water movement.

✓ Answer checked by Claude Opus 5.5 (high effort)

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