--- title: "Metamorphic rock, cleavage; igneous rock significance" subject: "Engineering Geology I" chapter: 4 key: "semester_3/engineering_geology_i:metamorphic-rock-cleavage-igneous-rock" source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/metamorphic-rock-cleavage-igneous-rock site: BCT Engineering --- # Metamorphic rock, cleavage; igneous rock significance Engineering Geology I · Chapter 4: Petrology - Asked in: 2065 Shrawan (old course), 2+4+2 marks - Video: [Geology Unit 5 - Notes 3: Metamorphic Rock Classification EDUCATIONAL](https://www.youtube.com/watch?v=tE4lkrTXQZA) — Eric Hultgren - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/metamorphic-rock-cleavage-igneous-rock - Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-4 ## Question Define metamorphic rock and its types. Explain the structure of metamorphic rock. Give the significance of igneous rocks in civil engineering activities. ## 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. ## Answer #### 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. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How is a metamorphic rock formed? A. Melting and cooling of magma B. Cementation of sediments C. Deposition of organic remains D. Pre-existing rock changes in the solid state by heat, pressure and fluids Answer: D. Change occurs without melting. (Key point: Metamorphic rock) 2. Which rocks are contact metamorphic? A. Hornfels, marble, quartzite B. Slate, phyllite, schist C. Mylonite, fault breccia D. Granite, basalt Answer: A. Caused by heat from nearby magma. (Key point: Contact type) 3. Regional metamorphism produces which rocks? A. Marble only B. Slate, phyllite, schist, gneiss C. Hornfels D. Mylonite Answer: B. Heat and pressure during mountain building. (Key point: Regional type) 4. Why are igneous rocks good for dam sites? A. Highly bedded and soft B. Very porous C. Massive, non-porous and unbedded, though joints and weathering must be checked D. Fissile Answer: C. Strong and durable. 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