UPSC Geology 2026 — Paper II

(a) Two linked demands: (i) 'Describe' the classification of crystals into crystal systems, i.e. set out the systems with their axial lengths and interaxial angles and the symmetry basis of the scheme; (ii) 'add a note on' the types of symmetry elements crystals show. Both parts must appear or the answer is incomplete. (b) 'Discuss' the structural classification of silicates, i.e. explain that the classes are defined by the degree of polymerisation of SiO4 tetrahedra, and set out each class with its anion group, Si:O ratio and representative minerals with formulae. (c) Define granitization and then 'explain' it as a rock-forming process - the mechanism (solid-state metasomatism, ionic diffusion, migrating fronts), the field and petrographic evidence, and its standing in the granite controversy relative to the magmatic hypothesis. (d) Two parts: (i) how granulites are identified on textural (and associated mineralogical) grounds, especially in thin section; (ii) a named list of the granulite-bearing metamorphic terrains of India. Both must be answered; the Indian localities carry real marks. (e) 'Outline' the petrographic criteria observed in thin section that are used both to identify sedimentary rocks and to classify them - i.e. textural parameters, framework/matrix/cement composition, the standard classification schemes for sandstones and carbonates, and diagenetic/porosity features.

• Seven systems with axial relations and angles: cubic, tetragonal, hexagonal (with trigonal), orthorhombic, monoclinic, triclinic
• Basis of classification: symmetry, in particular the characteristic axes
• Symmetry elements: plane, axes (2, 3, 4, 6-fold), centre
• 32 crystal classes
• Basis: linkage and polymerisation of SiO₄ tetrahedra
• Six classes: nesosilicates, sorosilicates, cyclosilicates, inosilicates (single and double chain), phyllosilicates, tectosilicates
• Si:O ratio or anion group for each class
• Mineral example for each class
• Definition: transformation of solid rock into granite without melting, by metasomatism
• Mechanism: ionic diffusion, migrating fronts, basic front and granite front
• Evidence: relict structures, gradational contacts, no chilled margins, room problem
• Magmatic versus granitization debate (Bowen)
• Granulite facies, high temperature, dry
• Granoblastic texture with polygonal grain boundaries at about 120°
• Diagnostic assemblage: orthopyroxene with clinopyroxene, plagioclase and garnet
• Indian terrains: Southern Granulite Terrane, Eastern Ghats, Central Indian Tectonic Zone, Chotanagpur
• Textural features: grain size, sorting, rounding, packing
• Composition: framework grains, matrix and cement
• Classification: QFL scheme for sandstones and Folk or Dunham for carbonates
• Diagenetic and porosity features

(a) 'Describe' the common rock-forming minerals of igneous rocks and of metamorphic rocks, and for each give its diagnostic (identifying) features - composition/formula, habit, cleavage, colour, and the optical criteria by which it is told apart from look-alikes. Both rock classes must be covered. (b) 'Give an account' of the optical properties of common rock-forming minerals and then explain 'how' those properties are applied at the petrological microscope - i.e. the systematic plane-polarised, crossed-polars and conoscopic routine that leads to identification. (c) Two parts: (i) define twinning and its elements and kinds; (ii) 'discuss' the specific twin laws found in the feldspar group - Carlsbad, Baveno, Manebach, albite, pericline and the combined cross-hatched twinning of microcline - with their twin planes/axes and petrographic significance.

• Igneous minerals: quartz, feldspars, micas, hornblende, augite, olivine, each with diagnostic properties
• Metamorphic minerals: garnet, staurolite, kyanite, sillimanite, andalusite, chlorite and others
• Diagnostic features such as colour, relief, cleavage, twinning, extinction and birefringence
• Both rock classes covered
• Plane-polarised properties: colour, pleochroism, relief, cleavage, habit
• Crossed-polar properties: birefringence and interference colour, extinction angle, twinning
• Conoscopic figure: uniaxial or biaxial, optic sign, 2V
• Stepwise identification routine
• Definition of twinning and the twin elements: plane, axis, composition plane
• Kinds of twins: contact, penetration, simple, polysynthetic, cyclic; and their origin
• Feldspar laws: Carlsbad, Baveno, Manebach, albite, pericline
• Combined albite and pericline (tartan) twinning in microcline, with the petrographic significance

(a) 'Discuss' how carbonatite magmas originate and evolve: define and classify carbonatites, set out and weigh the three competing petrogenetic models (primary mantle melt, liquid immiscibility, extreme fractionation), cite the geochemical and isotopic evidence, and note their tectonic setting and associations. (b) Two linked demands: define metasomatic replacement and give the criteria by which it is recognised; then analyse specifically how the chemical composition of the host (wall) rock governs where and what mineralisation is deposited - the reactive-carbonate, reductant and inert-host cases. (c) 'Discuss the evolution' of the Deccan Volcanic Province - its extent, volume and age, the plume and rift mechanism that produced it, its stratigraphy and petrology, its eruptive style and sub-provinces, and its environmental and landscape consequences.

• Definition and classification: over 50% carbonate; calcio-, magnesio-, ferro- and natrocarbonatite
• Three models: primary mantle melt, liquid immiscibility, fractional crystallisation
• Isotopic and geochemical evidence, such as mantle-like Sr, Nd and C–O isotopes and enrichment in Nb and REE
• Tectonic setting and association with alkaline silicate rocks and fenites
• Definition: volume-for-volume replacement by fluids with change in chemistry and preservation of texture
• Recognition criteria: pseudomorphs, relict structures, irregular fronts, no open-space filling
• Reactive carbonate hosts giving replacement ore and skarn
• Reducing hosts and inert hosts, the latter giving vein-type deposits
• Extent, volume and age: about 500,000 km² now, about 1 million km³, about 66 Ma near the K–Pg boundary
• Origin: Réunion plume and rifting, fissure eruptions and dyke swarms
• Stratigraphy and petrology: Kalsubai, Lonavala, Wai and Salsette subgroups, tholeiitic basalt, pahoehoe and aa flows, red boles, intertrappean beds
• Consequences: climate and extinction debate, regur and laterite, Western Ghats

(a) 'Discuss' the whole chain of primary processes that makes a sedimentary rock - weathering, erosion, transport, deposition - but with the explicit 'emphasis' demanded on diagenesis and lithification, i.e. compaction, cementation and the associated post-depositional changes. (b) 'Explain how' - a causal question. Trace the chain by which provenance, weathering, transport, sorting and depositional energy determine (i) the mineralogical composition and (ii) the porosity of the resulting sedimentary rock, using maturity concepts and packing relationships. (c) Two parts: (i) name and classify the major depositional environments of sedimentary rocks; (ii) 'discuss' the characteristic lithological, textural, structural and palaeontological features by which rocks of each environment are recognised.

• Chain of weathering, erosion, transport and deposition, each briefly explained
• Diagenesis defined, with its stages: eodiagenesis, mesodiagenesis, telodiagenesis
• Compaction, cementation, recrystallisation, replacement, dissolution and authigenesis with examples
• Lithification as compaction plus cementation, with its control on porosity
• Provenance, climate and relief control on the mineral supply
• Transport and sorting, giving compositional and textural maturity
• Porosity controlled by packing, sorting, rounding and matrix, with cubic 47.6% and rhombohedral 26%
• High-energy against low-energy deposits, and later compaction and cementation
• Classification into continental, transitional and marine environments
• Continental features: fluvial, alluvial fan, lacustrine, aeolian, glacial
• Transitional and marine features: deltaic, beach, tidal flat, reef, shelf, deep-sea turbidites
• Diagnostic lithology, structure and fossils for each

(a) Explain the relevance of the Law of the Sea (UNCLOS, 1982) to the management of marine mineral resources: the maritime zones and who owns the resources in each, the regime of the Area and the International Seabed Authority, and the Indian application. (b) 'Explain' both halves: the causes of sea-level rise (climatic - thermal expansion and land-ice melt - and non-climatic/local causes of relative rise) and its physical, ecological and socio-economic impacts, ideally with rates and examples. (c) 'Discuss the different types' of prospecting methods for metallic mineral deposits - i.e. classify them into direct/geological, geochemical, geophysical and physical/subsurface methods, and state what each detects and when it is used. (d) 'Explain' the causes of pollution of BOTH groundwater and surface water separately: point and diffuse anthropogenic sources for each, and, for groundwater, the geogenic causes (fluoride, arsenic) that dominate the Indian problem. (e) Two parts: 'discuss' the environmental costs imposed by growing urbanisation - on land, air, water, geology and waste - and then explain 'how' sustainability can be ensured, through planning, resource management and governance measures.

• UNCLOS 1982 zones: territorial sea 12 nm, contiguous zone 24 nm, EEZ 200 nm, continental shelf
• Sovereign rights over seabed minerals in the EEZ and shelf
• The Area as common heritage of mankind under the International Seabed Authority
• Indian application: ratification, nodule and sulphide contracts
• Global causes: thermal expansion and melting of glaciers and ice sheets
• Local causes of relative rise: subsidence, groundwater withdrawal, tectonics
• Physical impacts: inundation, erosion, surge, saline intrusion
• Ecological and socio-economic impacts with examples
• Geological methods: mapping, gossans, indicator minerals, pits and trenches
• Geochemical methods: soil, stream sediment and pathfinder elements
• Geophysical methods: magnetic, gravity, electrical, IP, EM, radiometric, with the ore each detects
• Drilling and sub-surface methods
• Surface water: sewage, industrial effluent, agricultural runoff, mining
• Groundwater: leachate from landfills, septic tanks and fertiliser, and over-pumping
• Geogenic fluoride and arsenic with Indian regions
• Comparison of the two
• Costs on land, air, water and geology, and waste
• Impervious surfaces, floods, subsidence and groundwater depletion
• Sustainability measures: planning, zoning, harvesting, recycling
• Governance and geoscientific input

(a) Two demands: 'explain the differences' between ore, ore mineral and gangue as distinct concepts (one economic, one mineralogical, one relational); then 'discuss their significance in mineral processing' - liberation, comminution, separation methods and the economics of concentration. (b) Two parts: 'how does tenor influence economic viability' - define tenor and link it through cut-off grade, tonnage, recovery, by-products and penalties to profitability; and 'what methods are used to determine it' - sampling, assaying and estimation. (c) A two-step reserve calculation: from a deposit volume of 2 million cubic metres and an average ore density of 2.5 tonnes per cubic metre, compute (i) the proven reserves in tonnes, and (ii) the quantity of copper contained in those reserves at an average grade of 3 per cent Cu. Both answers must be stated with units.

• Ore as an economic, profitable-to-extract aggregate; ore minerals as the valuable metal-bearing minerals; gangue as the valueless minerals
• Examples of each, such as chalcopyrite and galena as ore minerals and quartz and calcite as gangue
• Liberation by comminution and separation by gravity, magnetic and froth flotation
• Concentrate, tailings and slag, and the economics of concentration
• Tenor defined as average grade of the metal in the ore
• Link to viability through cut-off grade, tonnage, recovery, by-products and penalties
• Sampling methods: channel, chip, grab, core
• Assaying and estimation: chemical and instrumental assay, weighted average, geostatistics
• Tonnage = 2 × 10⁶ × 2.5 = 5 × 10⁶ tonnes
• Copper = 5 × 10⁶ × 0.03 = 1.5 × 10⁵ tonnes
• Both answers with units
• Steps of the working shown

(a) Two parts: 'describe' sampling - what it is, why representativeness governs it, and the theory behind sample size; and 'add a note on' the common geological sampling methods, i.e. grab, chip, channel, bulk, core and sludge sampling, with their reliability. (b) Two parts: 'explain the procedure' of ore reserve estimation as a sequence from data collection to classification; and state 'how tonnage and grade are calculated' - the actual formulae and the estimation methods, classical and geostatistical. (c) 'Explain' the beneficiation processes used to enrich sulphide ore minerals - i.e. the flowsheet from comminution and liberation through froth flotation (its principle, reagents and selective/differential circuits) to dewatering, plus the complementary gravity, magnetic and hydrometallurgical routes.

• Sampling defined, with the need for a representative sample
• Sample size: dependence on particle size, Richards–Czeczott Q = kd² or Gy's theory, and reduction by splitting
• Methods: grab, chip, channel, bulk, core, sludge
• Relative reliability of each method
• Steps: data collection, plotting, cut-off, blocking, calculation, classification
• Tonnage = volume × bulk density
• Weighted average grade, G = Σgw/Σw
• Estimation methods, classical and geostatistical (kriging)
• Comminution and liberation, with classification
• Froth flotation: principle and the roles of collector, frother, activator, depressant and pH
• Differential flotation for Cu–Pb–Zn ores and the cleaner and scavenger stages
• Dewatering; gravity, magnetic and hydrometallurgical methods

(a) Two subjects and two tasks: state the causes of earthquakes AND of volcanic activity, then 'discuss the mitigation possibilities' for both. All four elements must appear; an answer on earthquakes alone is half an answer. (b) 'What is the status' asks for an appraisal, not a list: set out the constitutional basis, the principal statutes and rules, the judicially developed principles and the institutions, and then assess how far implementation matches the legal architecture. (c) 'Explain the use' of elementary (primary) thermodynamics in understanding geological processes: the free-energy criterion, the Clausius-Clapeyron equation, the phase rule, chemical potential and the equilibrium constant, and their application to petrogenetic grids, geothermobarometry, fugacity buffers and melting - with the limits set by kinetics.

• Causes of earthquakes: tectonic elastic rebound, volcanic, induced and collapse
• Causes of volcanism: subduction, divergent boundaries, hotspots and plumes, with gas-driven eruption
• Earthquake mitigation: zoning, seismic design codes, retrofitting, early warning, preparedness
• Volcanic mitigation: monitoring, hazard maps, evacuation, lava diversion
• Constitutional basis: Articles 48A, 51A(g), 21 and 253
• Principal statutes: Water Act 1974, Air Act 1981, Environment (Protection) Act 1986, Wildlife, Forest and Biodiversity Acts, NGT Act 2010
• Judicial principles: polluter pays, precaution, absolute liability, public trust
• Institutions and an assessment of implementation gaps
• Free-energy criterion: G = H − TS, ΔG < 0 for spontaneity, ΔG = 0 at equilibrium
• Clapeyron equation dP/dT = ΔS/ΔV and slopes of reaction lines, with the Al₂SiO₅ or graphite–diamond example
• Phase rule and chemical potential
• Applications: petrogenetic grids, geothermobarometry, fugacity buffers, melting; limitation by kinetics