- Asked 2/29
- 2079 Bhadra · 4 marks
Texture and properties of four rocks
Short answer
Quartzite: granoblastic, massive, >90% quartz, strength 150-300 MPa, durable. Granite: holocrystalline, massive, quartz-feldspar-mica, strength 100-250 MPa, low porosity. Phyllite: lepidoblastic, foliated, mica-quartz, weak along foliation, poor for foundations. Conglomerate: rudaceous, bedded, pebbles in matrix, strength depends on cement; siliceous is strong, clayey weak.
Describe the texture, structure, mineral composition and engineering properties of quartzite, granite, phyllite and conglomerate.
| Rock | Texture | Structure | Minerals | Engineering properties |
|---|---|---|---|---|
| Quartzite (metamorphic) | Granoblastic, interlocking quartz grains | Massive, non-foliated | >90 % quartz | Very hard, strong (150 - 300 MPa), durable; good aggregate and foundation rock; hard to dress |
| Granite (igneous, plutonic) | Holocrystalline, phaneritic, granular | Massive, jointed | Quartz, feldspar, mica/hornblende | Strong (100 - 250 MPa), low porosity, durable, takes polish; foundation, dam, building and aggregate use |
| Phyllite (metamorphic) | Very fine grained, lepidoblastic, silky sheen | Foliated; phyllitic cleavage, often crinkled | Mica (sericite), chlorite, quartz | Weak along foliation, splits easily, weathers to clay; poor for foundations, tunnels and slopes |
| Conglomerate (sedimentary, clastic) | Rudaceous: rounded pebbles/gravel in finer matrix | Bedded, massive, poorly sorted | Pebbles of quartz, quartzite, etc.; cement of silica, calcite or iron oxide | Strength depends on the cement; siliceous cement is strong, clayey is weak; porous, leaks; used as aggregate and for rough walls |
✓ Answer checked by Claude Opus 5.5 (high effort)
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