🧭 Introduction

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Rocks form the solid foundation of the Earth’s crust and are the primary host of mineral deposits.

For DGMS examinations, understanding rock formation, classification, and transformations is essential to predict strata behavior, slope stability, and mine safety.
All rocks are classified into three main types — Igneous, Sedimentary, and Metamorphic — based on their origin and mode of formation.

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🔥 Igneous Rocks

• Formed by the solidification of molten magma.
• Classified as:
1. Intrusive (Plutonic) – Formed deep below Earth’s surface (e.g., Granite, Diorite).
2. Extrusive (Volcanic) – Formed on surface after volcanic eruption (e.g., Basalt, Rhyolite).
• Texture: Coarse in intrusive, fine in extrusive.
• Characteristics:

• Crystalline, hard, and massive.
• Contain minerals like quartz, feldspar, mica.
• Important for underground support assessment.

📘 Example for DGMS exams:
“Basalt” forms the Deccan Trap region — major overburden rock in Western Coalfields.

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🌊  Sedimentary Rocks

• Formed by deposition, compaction, and cementation of sediments.
• Often layered (stratified) and may contain fossils.
• Formed from pre-existing rocks through weathering, erosion, and transportation.
• Classified as:
• Clastic: Sandstone, shale, conglomerate.
• Chemical: Limestone, dolomite.
• Organic: Coal, chalk.
• Significance in Mining:
• Most coal and petroleum deposits occur in sedimentary basins.
• Bedding planes and joints are critical for slope stability.

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⚙️  Metamorphic Rocks

• Formed by alteration of existing rocks (igneous or sedimentary) under heat, pressure, or chemical activity.
• Process called Metamorphism.
• Classified as:
• Thermal (contact) metamorphism – due to heat.
• Regional metamorphism – due to pressure.
• Examples:
• Limestone → Marble
• Shale → Slate
• Sandstone → Quartzite
• Granite → Gneiss
• DGMS Tip: Metamorphic rocks often occur near faults and mineralized zones.

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🔄 The Rock Cycle

The rock cycle represents the continuous transformation between igneous, sedimentary, and metamorphic rocks. Example Cycle:
Magma → Igneous → Weathering → Sediments → Sedimentary → Heat/Pressure → Metamorphic → Melting → Magma again. This cycle ensures recycling of Earth’s materials, influencing mine geology and ore deposition.

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⚡ Quick One-Liners

• Igneous = formed by magma solidification.
• Sedimentary = layered, fossil-bearing.
• Metamorphic = transformed by heat/pressure.
• Deccan Trap = basaltic plateau (igneous).
• Coal = organic sedimentary rock.
• Gneiss = metamorphosed granite.
• Rock cycle = Earth’s natural recycling process.

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🖊️ Descriptive Model Answer

Q: Explain types of rocks and their significance in mining. 

Answer:
Rocks are classified into igneous, sedimentary, and metamorphic based on origin.

• Igneous rocks form the base and are massive (e.g., basalt).
• Sedimentary rocks contain coal and oil and show stratification (e.g., sandstone).
• Metamorphic rocks arise from transformation under heat/pressure (e.g., marble).
  The rock cycle connects all three through erosion, melting, and metamorphism.
  Knowledge of rock type helps assess ground control, slope design, and hazard prediction in mines.

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🎯 25 DGMS-Pattern MCQs 

Q1. Rocks formed from molten magma are called:
A. Sedimentary
B. Igneous
C. Metamorphic
D. Organic
E. Chemical
Answer: B.
Solution: Igneous rocks originate from cooling magma.

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Q2. The Deccan Trap mainly consists of:
A. Granite
B. Basalt
C. Shale
D. Limestone
E. Sandstone
Answer: B.
Solution: Deccan Trap = basaltic lava flow.

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Q3. The process of changing one rock type into another is:
A. Sedimentation
B. Erosion
C. Rock Cycle
D. Lithification
E. Cementation
Answer: C.
Solution: Rock cycle explains transformation among rock types.

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Q4. The metamorphism caused by high temperature is called:
A. Dynamic
B. Contact
C. Regional
D. Hydrothermal
E. Plutonic
Answer: B.
Solution: Contact metamorphism = heat from magma.

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Q5. Shale changes into:
A. Limestone
B. Slate
C. Marble
D. Quartzite
E. Sandstone
Answer: B.
Solution: Shale → Slate under low-grade metamorphism.

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Q6. Which of the following is a clastic sedimentary rock?
A. Shale
B. Marble
C. Basalt
D. Gneiss
E. Granite
Answer: A.
Solution: Clastic = composed of fragments (shale).

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Q7. The rock containing fossils is usually:
A. Igneous
B. Sedimentary
C. Metamorphic
D. Volcanic
E. Plutonic
Answer: B.
Solution: Fossils occur in sedimentary rocks.

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Q8. Granite is an example of:
A. Extrusive igneous rock
B. Intrusive igneous rock
C. Sedimentary rock
D. Metamorphic rock
E. None
Answer: B.
Solution: Granite forms deep underground.

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Q9. Sandstone under heat and pressure becomes:
A. Slate
B. Marble
C. Quartzite
D. Gneiss
E. Schist
Answer: C.
Solution: Sandstone → Quartzite.

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Q10. Coal is:
A. Organic sedimentary rock
B. Igneous rock
C. Metamorphic rock
D. Chemical sedimentary
E. Plutonic rock
Answer: A.
Solution: Formed from plant matter – organic sedimentary.

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Q11. The layering in sedimentary rocks is called:
A. Stratification
B. Foliation
C. Lamination
D. Banding
E. Grading
Answer: A.
Solution: Sedimentary rocks show distinct strata.

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Q12. Gneiss is derived from:
A. Granite
B. Limestone
C. Shale
D. Sandstone
E. Basalt
Answer: A.
Solution: Granite → Gneiss (high-grade metamorphism).

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Q13. Which rock type covers most of the Earth’s crust volume?
A. Sedimentary
B. Igneous
C. Metamorphic
D. Volcanic
E. Organic
Answer: B.
Solution: Igneous rocks dominate crust volume.

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Q14. The process of binding sediments into rock is called:
A. Cementation
B. Erosion
C. Crystallization
D. Melting
E. Faulting
Answer: A.
Solution: Cementation + compaction → lithification.

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Q15. Slate shows:
A. Stratification
B. Foliation
C. Bedding
D. Banding
E. Joints
Answer: B.
Solution: Foliation is common in metamorphic rocks.

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Q16. Which of the following is NOT a sedimentary rock?
A. Sandstone
B. Shale
C. Granite
D. Limestone
E. Coal
Answer: C.
Solution: Granite = igneous.

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Q17. The hardest among following is:
A. Slate
B. Limestone
C. Marble
D. Quartzite
E. Shale
Answer: D.
Solution: Quartzite is very hard and compact.

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Q18. Rock formed by deposition from solution is:
A. Chemical sedimentary
B. Organic sedimentary
C. Clastic sedimentary
D. Igneous
E. Metamorphic
Answer: A.
Solution: Precipitation of minerals = chemical.

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Q19. Which rock is mainly calcium carbonate?
A. Basalt
B. Granite
C. Limestone
D. Shale
E. Gneiss
Answer: C.
Solution: Limestone = CaCO₃.

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Q20. The term lithification means:
A. Rock breaking
B. Rock formation from sediments
C. Rock melting
D. Magma cooling
E. Soil erosion
Answer: B.
Solution: Lithification = process turning sediments to rock. 

Q21. The continuous process through which rocks are broken down, transported, and redeposited is called:
A. Rock deformation cycle
B. Erosion cycle
C. Metamorphism
D. Diagenesis
E. Crystallization
Answer: B.
Solution: The erosion cycle describes weathering, transport, and deposition, key to sedimentary rock formation in mining regions.

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Q22. In mining geology, erosion significantly affects:
A. Rock density
B. Ore grade
C. Overburden thickness and slope stability
D. Seismic activity
E. Magnetic anomalies
Answer: C.
Solution: Erosion alters topography, exposing ore zones or destabilizing benches in opencast mines.

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Q23. Metamorphism in mining regions can result in:
A. Reduction in mineral hardness
B. Formation of valuable metamorphic minerals like garnet, schist, or marble
C. Loss of metal content
D. Sedimentation of new coal seams
E. Formation of volcanic rocks
Answer: B.
Solution: Heat and pressure transform rocks, producing new minerals significant for metalliferous mining.

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Q24. Sedimentation in mining basins is crucial for the formation of:
A. Igneous intrusions
B. Plutonic deposits
C. Coal, limestone, and shale layers
D. Gneissic bands
E. Magnetic ores
Answer: C.
Solution: Sedimentary processes lead to accumulation of coal and limestone — key economic minerals in mining.

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Q25. DGMS emphasizes knowledge of erosion, metamorphism, and sedimentation because:
A. They determine rock color
B. They control ore distribution, slope design, and mine drainage planning
C. They are unrelated to mining
D. They affect plant growth only
E. They occur only in igneous terrains
Answer: B.
Solution: Understanding these processes helps in safe mine design, preventing slope failure and ensuring effective water management.

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                       🏁 Conclusion

Understanding rock types and their transformation is crucial for mine design, drilling, and hazard control. DGMS exams frequently test classification, examples, and metamorphic transformations.
Mastering this topic ensures conceptual clarity for Mining Geology & General Safety papers. 

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