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Rock forming minerals and significance
Short answer
Rock-forming minerals like quartz, feldspar, mica, calcite, clay minerals determine rock strength, durability, and behavior. Quartz gives strength but is abrasive; feldspar weathers to clay; mica causes low shear strength in schists; calcite dissolves forming cavities; clay minerals cause swelling and landslides.
What are rock forming minerals? Describe their engineering significance.
Rock-forming minerals are the common minerals that make up most of the rocks of the earth's crust. About a dozen groups form over 90% of rocks: quartz, feldspars, micas, amphiboles, pyroxenes, olivine, calcite, dolomite, clay minerals and garnet.
Important minerals and engineering significance
| Mineral | Properties | Engineering significance |
|---|---|---|
| Quartz | Hardness 7, chemically stable | Gives strength and durability to aggregates and concrete; abrasive, so it wears drill bits, tools and hydropower turbines; its content in river sediment is a key result of sediment analysis for hydropower |
| Feldspar | Hardness 6, weathers to clay | Rocks rich in feldspar (granite) are strong, but weathering produces clay and weakens the rock |
| Mica | Perfect cleavage, soft | Mica-rich schist/phyllite has low shear strength and fails along foliation; poor for aggregate |
| Calcite | Hardness 3, dissolves in acid water | Limestone is useful for cement, but dissolution forms cavities and solution channels, giving leakage at reservoirs |
| Clay minerals | Plastic, swelling (montmorillonite) | Cause swelling, low shear strength and landslides; being nearly impervious, clay soils are used for the impervious core of earth dams |
| Gypsum | Soluble, soft | Dissolves, causes settlement and attacks concrete |
| Pyroxene, amphibole, olivine | Dense, dark | Strong rocks (basalt, gabbro) good for aggregate, but alter easily |
| Pyrite | Oxidises to sulphuric acid | Attacks concrete and steel |
Thus, minerals decide the strength, hardness, solubility, weathering behaviour and suitability of rocks as foundation and construction material.
✓ Answer checked by Claude Opus 5.5 (high effort)
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