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Engineering significance of rock-forming minerals

Short answer

Quartz imparts hardness and durability but is abrasive and reactive forms can cause concrete expansion. Calcite dissolves in acidic water, creating solution cavities that threaten foundations and dams. Feldspar weathers to weak, swelling clay, reducing rock strength and causing slope failures. Mica's perfect cleavage makes rocks weak along foliation, leading to instability and poor aggregate.

Describe the engineering significance of rock-forming minerals (quartz, calcite, feldspar and mica).

The properties of rock-forming minerals decide the strength, durability and behaviour of rocks used in foundations, tunnels and construction materials.

  • Quartz (SiO₂): very hard (7), chemically stable, no cleavage. Rocks rich in quartz (granite, quartzite, sandstone) are strong, durable and resistant to weathering, so good for aggregate, foundations and building stone. Its abrasive nature wears drilling tools and crushers. Reactive (amorphous) silica can cause alkali-aggregate reaction in concrete.
  • Calcite (CaCO₃): soft (3), perfect cleavage, dissolves in acidic water. Limestone and marble make cement, lime and building stone. Solution cavities in limestone cause reservoir leakage and foundation settlement, a risk for dams.
  • Feldspar: hardness 6, two cleavages; weathers to clay minerals, so feldspar-rich rocks lose strength with weathering. The clay formed is weak, swells and is slippery, and can cause slope failure.
  • Mica: very perfect cleavage, soft, flaky. Rocks rich in mica (schist, phyllite) split easily, are weak along foliation, and cause slope and tunnel instability. Mica in aggregate reduces concrete strength.

✓ Answer checked by Claude Opus 5.5 (high effort)

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