Which of the following rock contain coal and petroleum?
- (a)Granite
- (b)Igneous rocks (generally)
- (c)Metamorphic (or transformed) rocks
- (d)Layered or sedimentary rocks
Correct — D, Layered or sedimentary rocks. Coal and petroleum both form from the burial and compaction of ancient organic matter — plant material for coal, marine organisms for petroleum — within layered sedimentary strata over geological time; sedimentary rocks such as sandstone, shale and limestone act as the source and reservoir rocks for these fossil fuels.
- (a)Granite — Granite is a coarse-grained igneous rock that crystallises from cooling magma; it contains no organic matter and cannot host coal or petroleum.
- (b)Igneous rocks (generally) — Igneous rocks form from solidifying molten magma or lava at high temperature, a process that destroys organic material rather than preserving it as fossil fuel.
- (c)Metamorphic (or transformed) rocks — Metamorphic rocks form when existing rocks recrystallise under intense heat and pressure — conditions that typically destroy fossil fuel deposits rather than create them (extreme metamorphism turns coal into graphite).
Coal and petroleum are fossil fuels that form only in sedimentary settings. Coal forms from thick accumulations of buried plant matter compressed over millions of years; petroleum forms from marine microorganisms buried in sediment and subjected to moderate heat and pressure. Both processes need the layered, low-temperature depositional environment unique to sedimentary rocks — igneous and metamorphic rocks form under conditions that destroy organic matter instead.
MPPSC/UPSC often test rock-type identification through a 'which rock hosts resource X' framing. The trap is picking a specific igneous rock like granite because it sounds familiar, or choosing metamorphic rocks by confusing their formation 'under pressure' with the very different, milder burial conditions that actually preserve fossil fuels.
- Sedimentary rocks form in layers from deposited sediment and organic matter
- Coal is compressed, carbonised plant matter found in sedimentary strata
- Petroleum is decomposed marine organic matter trapped in porous sedimentary rock
- Extreme metamorphism converts coal into graphite, destroying it as a fuel
- Picking a specific igneous rock (granite) instead of recognising the correct rock class (sedimentary)
- Confusing metamorphic 'pressure' with the low-heat burial conditions that actually preserve fossil fuels
Usually phrased as 'which type of rock contains coal/petroleum/fossils' — the answer is consistently sedimentary/layered/stratified rocks.
Consider the following statements made about the sedimentary rocks: I. Sedimentary rocks are formed at Earth's surface by the hydrological system. II. The formation of sedimentary rocks involves the weathering of pre-existing rocks. III. Sedimentary rocks contain fossils. IV. Sedimentary rocks typically occur in layers. Which of these statements are correct?
- (a) I and II
- (b) I and IV
- (c) II, III and IV
- (d) I, II, III and IV
Answer(d) I, II, III and IV — sedimentary rocks form at the surface via weathering and the hydrological cycle, occur in layers, and preserve fossils.
Same core idea — identifying the defining characteristics of sedimentary rocks (surface-formed, layered, weathering-derived, fossil-bearing), the rock class that also hosts coal and petroleum.
- practice — not a real PYQ
The four stages in the formation of coal, in order of increasing carbon content, are:
- (a)Peat → Lignite → Bituminous → Anthracite
- (b)Lignite → Peat → Anthracite → Bituminous
- (c)Anthracite → Bituminous → Lignite → Peat
- (d)Peat → Bituminous → Lignite → Anthracite
Answer(a) Peat → Lignite → Bituminous → Anthracite — the standard coalification sequence.
- practice — not a real PYQ
Fossils, used to date rock strata and identify past life forms, are typically preserved in which type of rock?
- (a)Igneous
- (b)Metamorphic
- (c)Sedimentary
- (d)Plutonic
Answer(c) Sedimentary — layered deposition preserves organisms before they decay.