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Aragón PAU Geology and Environmental Sciences study materials
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Aragón PAU Geology and Environmental Sciences practice questions

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Question 1Geology, Earth systems, resources, hazards and environmental evidence

Which type of tectonic plate boundary is characterized by plates moving away from each other, leading to upwelling mantle magmatism and the generation of new oceanic lithosphere?

  1. Convergent boundary
  2. Divergent boundary Correct answer.
  3. Transform fault boundary
  4. Passive continental margin

Explanation

Divergent plate boundaries occur where tectonic plates move apart. As plates separate, depressurization in the underlying asthenosphere causes partial melting, generating basaltic magma that cools to form new oceanic lithosphere at mid-ocean ridges.

Question 2Geology, Earth systems, resources, hazards and environmental evidence

In the mechanical (rheological) layering of the Earth's interior, which layer is characterized as a rigid, brittle outer shell comprising the entire crust and uppermost solid mantle?

  1. Asthenosphere
  2. Lithosphere Correct answer.
  3. Mesosphere
  4. Outer core

Explanation

The lithosphere is defined rheologically as the rigid, brittle outer layer of Earth, averaging 100 km in thickness, encompassing both the crust and the uppermost brittle portion of the mantle. It breaks into tectonic plates that float over the ductiles asthenosphere.

Question 3Geology, Earth systems, resources, hazards and environmental evidence

What is the primary difference in propagation mechanism between primary (P) seismic waves and secondary (S) seismic waves?

  1. P-waves are transverse shear waves that travel only through solids, while S-waves are longitudinal compressional waves that travel through all media
  2. P-waves are longitudinal compressional waves that travel through solids, liquids, and gases, while S-waves are transverse shear waves that propagate only through solids Correct answer.
  3. P-waves travel exclusively along the Earth's surface, while S-waves penetrate deep into the body of the Earth
  4. P-waves travel slower than S-waves in all earth materials

Explanation

P-waves (primary waves) are longitudinal compressional waves where particle vibration is parallel to propagation; they are the fastest body waves and propagate through solids, liquids, and gases. S-waves (secondary waves) are transverse shear waves with particle motion perpendicular to propagation, and because liquids have zero shear strength, S-waves cannot transmit through liquid media.

Question 4Geology, Earth systems, resources, hazards and environmental evidence

Which seismic evaluation scale measures the quantitative energy released at an earthquake's focus based on logarithmic instrumental wave amplitude, as opposed to qualitative surface damage observations?

  1. Modified Mercalli Scale
  2. Richter Magnitude Scale Correct answer.
  3. MSK Intensity Scale
  4. Saffir-Simpson Scale

Explanation

The Richter scale (and modern Moment Magnitude scale) measures earthquake magnitude, which is a quantitative logarithmic measurement of total energy released at the hypocenter. Intensity scales like the Modified Mercalli and MSK measure qualitative observed destruction and shaking effects on humans and structures at specific surface locations.

Question 5Geology, Earth systems, resources, hazards and environmental evidence

What type of geological fault is produced when tensional stress causes the hanging wall block to move downward relative to the footwall block?

  1. Reverse fault
  2. Normal fault Correct answer.
  3. Strike-slip fault
  4. Thrust fault

Explanation

A normal fault results from tensional tectonic stress (crustal extension), where gravity causes the hanging wall block to slip down relative to the footwall block.

Question 6Geology, Earth systems, resources, hazards and environmental evidence

In structural geology, what folded rock structure dips away from the axial plane and contains the stratigraphically oldest rock layers along its central core?

  1. Syncline
  2. Anticline Correct answer.
  3. Monocline
  4. Structural basin

Explanation

An anticline is an arch-like convex-upward fold where rock strata dip away from the central axial crest. According to the law of superposition, unless overturned, the oldest strata are exposed in the core of an anticline.

Question 7Geology, Earth systems, resources, hazards and environmental evidence

Which driving force of plate tectonics is generated when cold, dense oceanic lithosphere sinks into the less dense asthenosphere under the influence of gravity at subduction zones?

  1. Ridge push
  2. Slab pull Correct answer.
  3. Basal drag
  4. Tidal force

Explanation

Slab pull is considered the dominant mechanism driving plate motion. As an oceanic lithospheric plate cools and thickens away from a ridge, it becomes denser than the underlying asthenosphere. At subduction zones, the cold, heavy leading edge sinks, pulling the rest of the plate behind it.

Question 8Geology, Earth systems, resources, hazards and environmental evidence

When an oceanic plate collides with a continental plate at a convergent margin, why does the oceanic plate selectively undergo subduction into the mantle?

  1. The oceanic crust is thicker and richer in silica than continental crust
  2. The oceanic lithosphere is denser and thinner than continental lithosphere, consisting primarily of mafic basalt and gabbro Correct answer.
  3. Continental crust experiences higher thermal expansion, making it heavier than oceanic crust
  4. Subduction is determined solely by the direction of Earth's rotational Coriolis effect

Explanation

Oceanic lithosphere is composed of mafic igneous rocks (basalt and gabbro) rich in iron and magnesium (density ~3.0 g/cm³), making it significantly denser than granitic continental crust (density ~2.7 g/cm³). Thus, the denser oceanic plate subducts beneath the buoyant continental plate.

Question 9Geology, Earth systems, resources, hazards and environmental evidence

How does an Andean-type (thermal/subduction) orogeny differ fundamentally from a Himalayan-type (alpine/collisional) orogeny?

  1. Andean orogeny involves oceanic-continental subduction with intense calc-alkaline magmatism, whereas Himalayan orogeny involves continent-continent collision without subduction of continental crust Correct answer.
  2. Andean orogeny is formed by rifting and extension, while Himalayan orogeny is formed by strike-slip shearing
  3. Himalayan orogeny produces active volcanic arcs, while Andean orogeny lacks volcanic activity completely
  4. Andean orogeny occurs along passive margins, while Himalayan orogeny occurs at divergent oceanic ridges

Explanation

Andean-type orogeny occurs where an oceanic plate subducts beneath a continental margin, producing subduction-related magmatism, volcanic arcs, and accretionary prisms. Himalayan-type orogeny occurs after intervening ocean basins close, resulting in collision between two thick, buoyant continental blocks (e.g., India and Eurasia) leading to massive crustal thickening and thrusting without subduction of continental crust.

Question 10Geology, Earth systems, resources, hazards and environmental evidence

What magma generation mechanism occurs at subduction zones when volatile fluids (predominantly water) released from dehydrating subducted sediment lower the solidus melting point of the overlying mantle wedge?

  1. Decompression melting
  2. Flux melting (hydration melting) Correct answer.
  3. Thermal conduction melting
  4. Impact shock melting

Explanation

At subduction zones, hydrated minerals in the subducting oceanic slab undergo metamorphism and release water. This addition of volatiles into the overlying asthenospheric mantle wedge lowers the melting temperature (solidus) of peridotite, inducing flux melting.

Question 11Geology, Earth systems, resources, hazards and environmental evidence

According to Bowen's Reaction Series, which silicate mineral crystallizes at the highest temperatures from a cooling basaltic melt in the discontinuous reaction series?

  1. Quartz
  2. Olivine Correct answer.
  3. Biotite mica
  4. Sodium-rich plagioclase

Explanation

In Bowen's discontinuous reaction series, olivine (an isolated tetrahedra nesosilicate) is the first mineral to crystallize at high temperatures (~1200°C) from a mafic magma, followed by pyroxene, amphibole, and biotite as temperature decreases.

Question 12Geology, Earth systems, resources, hazards and environmental evidence

Why do felsic (granitic/rhyolitic) magmas trigger violently explosive volcanic eruptions compared to effusive Hawaiian-style eruptions of mafic (basaltic) magmas?

  1. Felsic magmas have lower silica content and lower viscosity, allowing trapped gases to escape easily
  2. Felsic magmas have high silica content, lower temperatures, and high viscosity, which traps expanding gases under extreme pressure until violent fragmentation occurs Correct answer.
  3. Mafic magmas contain significantly higher dissolved water and gas content than felsic magmas
  4. Felsic eruptive vents are located exclusively deep underwater where hydrostatic pressure amplifies explosions

Explanation

Felsic magmas are rich in SiO2 (>65%), forming complex polymerized silicate chains that give them high viscosity. Combined with lower eruption temperatures and high volatile content, expanding gas bubbles cannot escape smoothly, leading to extreme pressure build-up and explosive pyroclastic eruptions.

Question 13Geology, Earth systems, resources, hazards and environmental evidence

What type of metamorphism is primarily driven by high thermal gradients adjacent to intrusive igneous bodies, producing non-foliated rocks such as hornfels?

  1. Regional metamorphism
  2. Contact (thermal) metamorphism Correct answer.
  3. Cataclastic (dynamic) metamorphism
  4. Hydrothermal metamorphism

Explanation

Contact (thermal) metamorphism occurs when host rocks are heated by proximity to hot igneous intrusions. Because directional differential stress is minimal, contact metamorphism recrystallizes minerals into fine-grained, tough, non-foliated rocks known as hornfels within a metamorphic aureole.

Question 14Geology, Earth systems, resources, hazards and environmental evidence

Which structural feature differentiates a thrust fault from a standard reverse fault?

  1. A thrust fault is a high-angle reverse fault dipping at greater than 60°
  2. A thrust fault is a low-angle reverse fault with a fault plane dip of less than 45° (typically < 30°), transporting older rocks over younger strata across large lateral distances Correct answer.
  3. A thrust fault is produced by tensional stress, while a reverse fault is produced by shear stress
  4. A thrust fault exhibits vertical movement exclusively along strike-slip faults

Explanation

Both thrust faults and reverse faults are compressional dip-slip structures where the hanging wall moves up relative to the footwall. A thrust fault is specifically distinguished by a low dip angle (<45°, often <30°), allowing large-scale horizontal displacement of nappes.

Question 15Geology, Earth systems, resources, hazards and environmental evidence

What seismic discovery provided definitive evidence for the existence of Earth's liquid outer core?

  1. The complete absence of S-wave arrivals (S-wave shadow zone) on seismograms at epicentral distances greater than 103° Correct answer.
  2. The sudden acceleration of P-waves at the Mohorovičić discontinuity
  3. The observation that surface waves travel faster through continental crust than ocean crust
  4. The reflection of P-waves at the lithosphere-asthenosphere boundary

Explanation

Because transverse S-waves cannot travel through liquid media, seismic waves penetrating deep enough to hit the outer core are stopped. This creates a global S-wave shadow zone beyond 103° epicentral distance, proving the outer core is liquid.

Question 16Geology, Earth systems, resources, hazards and environmental evidence

Which metamorphic facies assemblage develops under conditions of high pressure but relatively low temperature, typically diagnostic of deep subduction zone metamorphism?

  1. Greenschist facies
  2. Blueschist facies (glaucophane-bearing) Correct answer.
  3. Granulite facies
  4. Pyroxene-hornfels facies

Explanation

Blueschist facies forms under high pressure and low temperature conditions characteristic of rapid subduction of cold oceanic lithosphere into the mantle. The distinctive blue color comes from the sodic amphibole glaucophane.

Question 17Geology, Earth systems, resources, hazards and environmental evidence

Under experimental rock mechanics, how do increasing confining pressure and ambient temperature affect the strain behavior of crustal rocks?

  1. They cause rocks to transition from ductile plastic deformation to brittle fracturing
  2. They increase rock strength, making all materials undergo elastic rebound exclusively
  3. They raise the yield point and expand the ductile deformation field, allowing rocks to fold without fracturing Correct answer.
  4. They eliminate strain entirely by suppressing tectonic stress

Explanation

High confining pressure and elevated temperature deep in the crust suppress brittle fracture and increase the range of ductile (plastic) deformation. Consequently, rocks deep in the crust fold smoothly under stress, whereas cold, low-pressure shallow rocks fracture brittly into faults.

Question 18Geology, Earth systems, resources, hazards and environmental evidence

A paleomagnetic survey across a symmetrical mid-ocean ridge identifies a normal magnetic anomaly stripe 40 km wide located 120 km from the ridge crest. Radiometric dating of basalt samples in this anomaly yields an age of 4.0 million years. What is the full spreading rate of the ocean basin?

  1. 30 km / million years (3.0 cm/year)
  2. 60 km / million years (6.0 cm/year) Correct answer.
  3. 15 km / million years (1.5 cm/year)
  4. 120 km / million years (12.0 cm/year)

Explanation

Half-spreading rate = Distance to ridge / Age = 120 km / 4.0 Ma = 30 km/Ma (or 3.0 cm/year on one side). Since mid-ocean ridges spread symmetrically on both sides, the full ocean basin spreading rate is twice the half-rate: 2 × 30 km/Ma = 60 km/Ma (6.0 cm/year).

Question 19Geology, Earth systems, resources, hazards and environmental evidence

Which of the following processes is classified as a mechanical (physical) weathering mechanism?

  1. Hydrolysis of potassium feldspar into kaolinite clay
  2. Frost wedging (gelifraction) caused by freeze-thaw water expansion Correct answer.
  3. Dissolution of limestone by carbonic acid
  4. Oxidation of iron-rich minerals into hematite

Explanation

Frost wedging (gelifraction) is a mechanical weathering process where water enters rock fractures, freezes, expands by ~9% in volume, and mechanically breaks the rock apart without altering its chemical composition.

Question 20Geology, Earth systems, resources, hazards and environmental evidence

What cross-sectional shape is characteristic of a valley eroded primarily by alpine glacial activity, as compared to a V-shaped valley formed by river erosion?

  1. Flat-bottomed rectangular valley
  2. U-shaped valley (trough) Correct answer.
  3. Steep vertical slot canyon
  4. Asymmetrical W-shaped valley

Explanation

Glaciers fill the entire width of mountain valleys and erode both the floor and walls through plucking and abrasion, carving out a broad, steep-sided U-shaped glacial trough. Rivers cut downward, creating V-shaped valleys.

Question 21Geology, Earth systems, resources, hazards and environmental evidence

In karst geomorphology, what closed, bowl-shaped surface depression is formed by the solution of surface limestone or the collapse of an underlying cave roof?

  1. Doline (sinkhole) Correct answer.
  2. Polje
  3. Lapiaz (karren)
  4. Stalagmite

Explanation

A doline (or sinkhole) is a classic surface karst landform consisting of a circular or oval depression created either by chemical dissolution of bedrock at the surface or by collapse of subterranean cave voids.

Question 22Geology, Earth systems, resources, hazards and environmental evidence

Along a meandering river channel, where do maximum flow velocity and active bank erosion occur?

  1. On the inner bank (point bar)
  2. On the outer bank (cut bank) Correct answer.
  3. Directly along the streambed center regardless of curvature
  4. Uniformly across the entire channel cross-section

Explanation

Centrifugal force and momentum push the thalweg (fastest flow current) toward the outer bank of a meander curve. High kinetic energy causes active undercut erosion along the cut bank, while slower water on the inner bend deposits sediment to form a point bar.

Question 23Geology, Earth systems, resources, hazards and environmental evidence

What coastal landform is created when wave refraction concentrates erosion on a protruding headland, cutting a passage completely through the rock promontory?

  1. Sea arch Correct answer.
  2. Sea stack
  3. Spit
  4. Tombolo

Explanation

When waves attack both sides of a narrow headland, sea caves erode inward until they merge, forming a sea arch. When the arch roof eventually collapses, the isolated rock pillar left standing offshore becomes a sea stack.

Question 24Geology, Earth systems, resources, hazards and environmental evidence

In a well-developed soil profile, which horizon is known as the zone of accumulation (illuviation) where clay minerals, iron oxides, and soluble salts leached from upper layers concentrate?

  1. O horizon
  2. A horizon
  3. B horizon Correct answer.
  4. C horizon

Explanation

The B horizon (subsoil) is the zone of illuviation, where fine clays, iron, aluminum oxides, and carbonates washed down from the overlying A and E horizons accumulate.

Question 25Geology, Earth systems, resources, hazards and environmental evidence

Chemical weathering of limestone (calcium carbonate, CaCO3) proceeds primarily through carbonation. Which chemical equation correctly represents this reversible weathering reaction?

  1. CaCO3 + H2O + CO2 ⇌ Ca(HCO3)2 Correct answer.
  2. 2FeS2 + 7O2 + 2H2O → 2FeSO4 + 2H2SO4
  3. 2KAlSi3O8 + 2H2CO3 + 9H2O → Al2Si2O5(OH)4 + 4H4SiO4 + 2K+ + 2HCO3-
  4. CaSO4 + 2H2O ⇌ CaSO4·2H2O

Explanation

Limestone carbonation occurs when rainwater absorbs atmospheric and soil CO2 to form carbonic acid (H2CO3), which reacts with insoluble calcium carbonate (CaCO3) to form soluble calcium bicarbonate [Ca(HCO3)2]. Reversing this reaction precipitates CaCO3 speleothems in caves.

Question 26Geology, Earth systems, resources, hazards and environmental evidence

According to the Hjulström diagram governing stream transport, why does fine-grained clay require higher current velocity to erode from a streambed than medium-grained sand?

  1. Clay particles have higher particle mass than sand grains
  2. Cohesive electrostatic attraction and flat molecular geometry between fine clay particles create strong inter-particle bonding Correct answer.
  3. Sand grains absorb water and expand, anchoring themselves to the channel bottom
  4. Clay particles reside exclusively in high-velocity turbulent eddies

Explanation

Although individual clay particles are extremely tiny (<0.002 mm), their flat phyllosilicate structure and electrochemically charged surfaces cause them to stick together cohesively. Overcoming this inter-particle cohesion to initiate erosion requires higher stream power than eroding non-cohesive sand grains (~0.5 mm).

Question 27Geology, Earth systems, resources, hazards and environmental evidence

Under what hydrochemical conditions inside a limestone cave system does degassing of CO2 trigger the formation of stalactites and stalagmites?

  1. Dripping water loses CO2 to the cave atmosphere, decreasing acidity and driving calcium carbonate precipitation Correct answer.
  2. Dripping water absorbs CO2 from the cave air, increasing acidity and dissolving existing speleothems
  3. Cave temperatures drop below freezing, forcing mechanical ice precipitation
  4. Sulfide oxidation converts cave water into sulfuric acid

Explanation

Seep water under high soil CO2 pressure enters a cave where partial pressure of CO2 is lower. The water degasses (loses CO2), which lowers carbonic acid concentration, raises pH, and shifts the carbonate equilibrium Ca(HCO3)2 ⇌ CaCO3↓ + H2O + CO2↑ to precipitate solid calcite.

Question 28Geology, Earth systems, resources, hazards and environmental evidence

What unsorted, unstratified sediment mixture is deposited directly by melting glacial ice without water sorting?

  1. Outwash (tillite)
  2. Glacial till (drift) Correct answer.
  3. Varves
  4. Loess

Explanation

Glacial till is sediment deposited directly by melting ice. Because solid ice drops its load indiscriminately, till is characteristically unsorted (ranging from fine clay to giant boulders) and unstratified.

Question 29Geology, Earth systems, resources, hazards and environmental evidence

How does longshore drift redistribute beach sediment along a coastline?

  1. Waves approaching the shore at an oblique angle move sand up the beach face via swash, while backwash pulls sand straight down the slope under gravity Correct answer.
  2. Deep ocean currents push sand parallel to the coast outside the breaker zone
  3. Tidal bores lift sand vertically and transport it exclusively offshore into submarine canyons
  4. Wind blows sand dunes sideways into deep coastal estuaries

Explanation

Waves breaking obliquely push sand up the beach slope at an angle (swash). The returning backwash pulls sand straight down perpendicular to the shoreline under gravity. This zig-zag movement transports sand continuously parallel to the coast as longshore drift.

Question 30Geology, Earth systems, resources, hazards and environmental evidence

Which dune type is crescent-shaped with its horns pointing downwind, formed in arid regions with limited sand supply and a constant unidirectional wind direction?

  1. Barchan dune Correct answer.
  2. Parabolic dune
  3. Transverse dune
  4. Star dune

Explanation

Barchan dunes are solitary crescent-shaped dunes formed where sand supply is limited and wind blows from one dominant direction. The crescent tips (horns) point downwind because the outer edges move faster than the thick center.

Question 31Geology, Earth systems, resources, hazards and environmental evidence

What type of mass movement involves extremely slow, imperceptible downhill movement of soil and regolith under repeated freeze-thaw or wet-dry cycles, evidenced by tilted fence posts and curved tree trunks?

  1. Rockfall
  2. Debris flow
  3. Soil creep Correct answer.
  4. Slump (rotational slide)

Explanation

Soil creep is the slowest form of mass wasting (mm/year). Expansion (freezing/wetting) lifts soil particles perpendicular to the slope, and contraction (thawing/drying) drops them straight down under gravity, producing slow net downhill transport.

Question 32Geology, Earth systems, resources, hazards and environmental evidence

The famous Torcal de Antequera and Pyrenean karst formations in Spain demonstrate advanced dissolution landscape development. What hydrogeological risk is uniquely associated with subterranean karst aquifers?

  1. High vulnerability to rapid groundwater contamination due to fast conduit flow without natural filtration Correct answer.
  2. Complete absence of groundwater recharge due to impermeable limestone bedrock
  3. Excessive natural fluoride enrichment preventing human agricultural use
  4. Permanent liquefaction of surface topsoils under seismic shaking

Explanation

Karst aquifers contain open dissolution conduits and caves where groundwater flows rapidly (meters to kilometers per day). Because water bypasses granular soil filtration, surface pollutants (pesticides, sewage, nitrates) enter underground streams rapidly without natural purification.

Question 33Geology, Earth systems, resources, hazards and environmental evidence

What is the primary geomorphic function of a river's base level?

  1. It represents the highest elevation where a river initiates headward erosion
  2. It is the lowest elevation to which a stream can erode its channel, ultimate base level being sea level Correct answer.
  3. It marks the transition between turbulent and laminar water flow
  4. It is the maximum water depth achieved during 100-year flood events

Explanation

Base level is the lower limit of stream erosion. Sea level is the ultimate base level; lakes or resistant bedrock ledges act as local or temporary base levels. Below base level, a stream cannot cut down vertically and will deposit its sediment load.

Question 34Geology, Earth systems, resources, hazards and environmental evidence

In salt weathering (haloclasty), by what specific physical process do salt crystals disrupt rock structure in arid or coastal environments?

  1. Salt crystals dissolve rock minerals through acid hydrolysis
  2. Evaporation precipitates salt crystals within rock pores; subsequent thermal expansion or hydration causes high pressure against pore walls, fracturing the rock Correct answer.
  3. Salt ions replace silica tetrahedra in quartz crystals, turning them into soft gypsum
  4. Salt crusts absorb solar radiation, causing internal nuclear fission

Explanation

Haloclasty occurs when saline water enters rock pore spaces and evaporates. Growing salt crystals exert mechanical growth pressure against pore walls. Upon re-wetting or temperature changes, hydrated salts expand further, forcing rock grains apart (honeycomb weathering).

Question 35Geology, Earth systems, resources, hazards and environmental evidence

How do river terraces form along a valley cross-section over geological time?

  1. By continuous lateral sediment deposition during prolonged high-stand sea levels
  2. Through alternating periods of floodplain aggradation followed by renewed vertical channel incision caused by base level drop or tectonic uplift Correct answer.
  3. From volcanic basalt flows capping active river channels
  4. Through glacial ice carving step-like benches along valley sides

Explanation

River terraces are abandoned former floodplains left perched above the active river channel. They form when a river first deposits a flat alluvial valley floor (aggradation) and then undergoes renewed vertical downcutting (incision) due to tectonic uplift or sea level fall.

Question 36Geology, Earth systems, resources, hazards and environmental evidence

In periglacial environments, what process causes solifluction lobes to form on gentle slopes underlain by permafrost?

  1. The summer thaw melts the active surface layer, which becomes water-saturated and flows plastically over the impermeable frozen permafrost sublayer Correct answer.
  2. Subterranean ice caves collapse under glacial loading
  3. Wind transport deposits thick loess blankets that slump under gravity
  4. Bedrock undergoes rapid thermal expansion under intense solar radiation

Explanation

Solifluction occurs in periglacial regions where permafrost forms an impermeable barrier to water drainage. In summer, the upper active layer thaws, becoming saturated with water. Reduced internal friction causes this slurry layer to flow slowly downslope over the frozen substrate.

Question 37Geology, Earth systems, resources, hazards and environmental evidence

Which of the following physical criteria is part of the strict scientific definition of a mineral?

  1. Synthetic laboratory synthesis
  2. Ordered internal atomic (crystalline) structure Correct answer.
  3. Liquid state at room temperature
  4. Variable organic hydrocarbon composition

Explanation

A mineral is defined as a naturally occurring, inorganic solid with a definite chemical composition and an ordered internal atomic arrangement (crystalline structure).

Question 38Geology, Earth systems, resources, hazards and environmental evidence

On the Mohs Hardness Scale, which mineral serves as the reference standard for hardness rank 10?

  1. Talc
  2. Quartz
  3. Corundum
  4. Diamond Correct answer.

Explanation

Diamond is the hardest known natural mineral, occupying position 10 on Mohs scale. Talc is rank 1, Quartz is rank 7, and Corundum is rank 9.

Question 39Geology, Earth systems, resources, hazards and environmental evidence

What texture characterizes an igneous rock that cooled slowly deep within the Earth's crust, allowing large, visible mineral crystals to grow?

  1. Aphanitic (fine-grained)
  2. Phaneritic (coarse-grained) Correct answer.
  3. Glassy
  4. Vesicular

Explanation

Phaneritic texture consists of coarse mineral grains large enough to be identified with the naked eye, typical of plutonic intrusive rocks (e.g., granite, diorite, gabbro) formed by slow underground cooling.

Question 40Geology, Earth systems, resources, hazards and environmental evidence

Which of the following sedimentary rocks is classified as a clastic (detrital) sedimentary rock formed from cemented rock fragments and mineral grains?

  1. Sandstone Correct answer.
  2. Rock salt (Halite)
  3. Chalk
  4. Bituminous coal

Explanation

Sandstone is a detrital/clastic sedimentary rock composed of sand-sized mineral grains or rock fragments (0.0625 to 2 mm) cemented together.

Question 41Geology, Earth systems, resources, hazards and environmental evidence

What metamorphic texture exhibits a planar, layered alignment of platy minerals (such as micas) produced by directed differential stress?

  1. Porphyroblastic
  2. Foliation Correct answer.
  3. Granoblastic
  4. Crystalline

Explanation

Foliation refers to the parallel planar alignment of platy or elongate minerals (like micas and amphiboles) under directional pressure, characteristic of slate, schist, and gneiss.

Question 42Geology, Earth systems, resources, hazards and environmental evidence

In the Rock Cycle, by what process do existing igneous, sedimentary, or metamorphic rocks transform into magma?

  1. Lithification
  2. Melting Correct answer.
  3. Crystallization
  4. Metamorphism

Explanation

Melting occurs when elevated temperature, reduced pressure, or addition of flux volatiles transforms solid rock into liquid magma within the mantle or lower crust.

Question 43Geology, Earth systems, resources, hazards and environmental evidence

What structural feature forms the basic fundamental building block of all silicate minerals?

  1. Silicon-oxygen tetrahedron (SiO4^4-) Correct answer.
  2. Carbonate ion (CO3^2-)
  3. Sulfate ion (SO4^2-)
  4. Sodium chloride cubic lattice (NaCl)

Explanation

The silica tetrahedron consists of one central silicon ion (Si4+) surrounded by four oxygen ions (O2-) arranged in a pyramid shape [SiO4]^4-. Silicate minerals are classified based on how these tetrahedra share oxygen corner atoms (isolated, chains, sheets, 3D frameworks).

Question 44Geology, Earth systems, resources, hazards and environmental evidence

How does the continuous branch of Bowen's Reaction Series change mineral composition during progressive magma cooling?

  1. It transforms olivine step-by-step into pyroxene, amphibole, and biotite
  2. Calcium-rich plagioclase (anorthite) continuously exchanges calcium and aluminum for sodium and silicon to become sodium-rich plagioclase (albite) Correct answer.
  3. Quartz breaks down into iron oxides and magnesium silicates
  4. Magma separates into immiscible sulfide and silicate liquid phases

Explanation

The continuous branch involves plagioclase feldspar. At high temperatures, calcium-rich plagioclase (anorthite) crystallizes. As cooling proceeds, Na+ and Si4+ continually replace Ca2+ and Al3+ in the crystal lattice without changing the crystal structure, yielding sodium-rich plagioclase (albite).

Question 45Geology, Earth systems, resources, hazards and environmental evidence

Which intrusive-extrusive rock pair is commonly treated as a felsic compositional counterpart, while differing in cooling history and texture?

  1. Gabbro and Basalt
  2. Diorite and Andesite
  3. Granite and Rhyolite Correct answer.
  4. Peridotite and Komatiite

Explanation

Granite (intrusive) and Rhyolite (extrusive) are compositional equivalents rich in quartz, potassium feldspar, and sodium plagioclase (felsic composition).

Question 46Geology, Earth systems, resources, hazards and environmental evidence

What textural distinction separates a conglomerate from a sedimentary breccia?

  1. Conglomerate consists of rounded clasts indicating long-distance transport, whereas breccia consists of angular clasts indicating minimal transport Correct answer.
  2. Conglomerate is formed by chemical precipitation, whereas breccia is formed by organic accumulation
  3. Breccia has sand-sized grains, while conglomerate has clay-sized grains
  4. Conglomerate contains quartz exclusively, while breccia contains calcite exclusively

Explanation

Both rocks contain gravel-sized clasts (>2 mm). In a conglomerate, clasts are well-rounded due to abrasion during long transport (e.g., rivers or beaches). In a breccia, clasts remain sharp and angular, indicating short transport near the source (e.g., alluvial fans or fault zones).

Question 47Geology, Earth systems, resources, hazards and environmental evidence

In what depositional sequence do evaporite minerals precipitate from a body of evaporating seawater as concentration increases?

  1. Halite first, followed by gypsum/anhydrite, and finally potassium salts (sylvite)
  2. Calcium carbonate (calcite/aragonite) first, followed by gypsum, halite, and lastly potassium/magnesium salts Correct answer.
  3. Sylvite first, followed by halite, gypsum, and calcite
  4. Quartz first, followed by feldspar, olivine, and biotite

Explanation

As seawater evaporates, minerals precipitate in order of solubility: Calcium carbonate (calcite) precipitates when 50% of water volume remains; Gypsum (CaSO4·2H2O) at 80% volume loss (~19% volume remaining); Halite (NaCl) at 90% volume loss (~10% volume remaining); and highly soluble potassium salts (sylvite, carnallite) at >95% volume loss.

Question 48Geology, Earth systems, resources, hazards and environmental evidence

What is the correct sequence of progressive regional metamorphic grade elevation starting from a mudstone/shale protolith?

  1. Gneiss → Schist → Phyllite → Slate
  2. Slate → Phyllite → Schist → Gneiss → Migmatite Correct answer.
  3. Hornfels → Marble → Quartzite → Migmatite
  4. Greenstone → Amphibolite → Blueschist → Eclogite

Explanation

Low-to-high regional metamorphism of pelitic shale proceeds: Slate (low grade, slaty cleavage) → Phyllite (sheen from microscopic mica) → Schist (coarse visible micas) → Gneiss (banded light/dark minerals) → Migmatite (partial melting bridge to igneous).

Question 49Geology, Earth systems, resources, hazards and environmental evidence

How does dolostone (dolomite rock) form from pre-existing calcite limestone during diagenesis (dolomitization)?

  1. Magnesium ions (Mg2+) in circulating pore fluids replace half of the calcium ions (Ca2+) in calcite to form CaMg(CO3)2 Correct answer.
  2. Silica replaces carbonate ions to convert calcite into quartz
  3. Limestone reacts with sulfuric acid to produce gypsum
  4. Calcite undergoes thermal melting to produce ultramafic carbonatite

Explanation

Dolomitization occurs when Mg-rich groundwater or brine circulates through porous calcite (CaCO3) limestone. Mg2+ ions substitute for Ca2+ ions in the crystal lattice: 2CaCO3 + Mg2+ → CaMg(CO3)2 + Ca2+.

Question 50Geology, Earth systems, resources, hazards and environmental evidence

The minerals kyanite, andalusite, and sillimanite are polymorphs sharing the chemical formula Al2SiO5. How are these minerals utilized as index minerals in metamorphic petrology?

  1. They define exact pressure-temperature (P-T) stability fields, allowing petrologists to determine the precise metamorphic P-T path of metamorphic rocks Correct answer.
  2. They indicate the degree of chemical weathering experienced by surface soils
  3. They measure the exact radiometric age of granitic intrusions
  4. They mark the transition between marine and terrestrial sedimentary environments

Explanation

Because kyanite (high P, low/mod T), andalusite (low P, high T), and sillimanite (high P, high T) share identical composition Al2SiO5 but distinct crystal structures, their phase boundaries in P-T space establish specific metamorphic zones (index minerals) and geothermobarometric paths.