RBSE SS Geology cheat sheet

Bowen's reaction series order (discontinuous branch): olivine → pyroxene → amphibole → biotite; continuous branch: Ca-rich plagioclase → Na-rich plagioclase; quartz and K-feldspar crystallize last from residual melt.

Mohs hardness: talc 1, gypsum 2, calcite 3, fluorite 4, apatite 5, orthoclase 6, quartz 7, topaz 8, corundum 9, diamond 10; fingernail ≈2.5, copper coin ≈3.5, steel knife ≈5.5, glass ≈5.5.

Isostasy: Airy model compensates by root thickness (thicker crust under mountains); Pratt model compensates by lateral density variation at a constant depth of compensation.

Fluvial transport thresholds: entrainment depends on grain size, velocity and depth; clay resists erosion by cohesion, sand is easiest to move, pebbles require highest velocity (Hjulström-type curve).

Glacial landforms: erosional - cirque, arête, horn, U-shaped valley, roche moutonnée; depositional - moraine (terminal/lateral/ground), drumlin, esker, kame, outwash plain.

Karst features form by carbonic-acid dissolution of limestone: sinkholes, dolines, poljes, lapies, stalactites (ceiling), stalagmites (floor), columns where they join.

Wind action: deflation produces blowouts and desert pavement; abrasion produces ventifacts and yardangs; deposition produces barchan (horns downwind), transverse, longitudinal and parabolic dunes.

Mass wasting classification by material and motion: fall, slide (rotational/translational), flow (debris flow, mudflow, creep); water content and slope angle are the main controls.

Crystal systems (7) with axial constraints: cubic a=b=c, α=β=γ=90°; tetragonal a=b≠c; orthorhombic a≠b≠c, all 90°; monoclinic α=γ=90°, β≠90°; triclinic all unequal; hexagonal/trigonal a=b≠c with γ=120°.

Symmetry elements: 32 crystal classes (point groups), 14 Bravais lattices, 230 space groups; 7 crystal systems derived from 6 (or 7) axial relationships.

Miller indices (hkl) are reciprocals of axial intercepts, cleared of fractions; (hkl) denotes a face, {hkl} a form; d-spacing from Bragg: nλ = 2d sinθ.

Silicate classification by SiO4 polymerization: nesosilicate (isolated, olivine), sorosilicate (double tetrahedra, epidote), cyclosilicate (rings, beryl, tourmaline), inosilicate (single chain pyroxene, double chain amphibole), phyllosilicate (sheets, mica, clay), tectosilicate (framework, quartz, feldspar).

Pleochroism and birefringence are optical properties observed under the petrographic microscope with crossed polars; isotropic minerals (cubic, amorphous) remain dark through a full 360° rotation.

Polymorphism examples: diamond–graphite (C), calcite–aragonite (CaCO3), kyanite–andalusite–sillimanite (Al2SiO5), quartz–tridymite–cristobalite.

Mineral identification in hand specimen: lustre, colour, streak, cleavage (number and angle), fracture, hardness, specific gravity, and special properties such as magnetism (magnetite) or effervescence with dilute HCl (calcite).

Common rock-forming minerals: quartz, feldspars (orthoclase, plagioclase), micas (biotite, muscovite), amphibole (hornblende), pyroxene (augite), olivine, calcite, dolomite, clay minerals.

Igneous classification by SiO2: ultramafic <45%, mafic 45–52%, intermediate 52–63%, felsic >63%; plutonic equivalents: peridotite, gabbro, diorite, granite; volcanic: komatiite, basalt, andesite, rhyolite.

Magma series: tholeiitic (low K, iron-enrichment trend), calc-alkaline (subduction, andesite–dacite–rhyolite), alkaline (high Na+K, e.g. nephelinite, phonolite).

Igneous textures record cooling history: phaneritic (slow, plutonic), aphanitic (fast, volcanic), porphyritic (two-stage), glassy (obsidian), vesicular (pumice, scoria), pyroclastic.

Sedimentary rock classification: clastic by grain size (rudaceous, arenaceous, argillaceous); chemical/biochemical (limestone, dolomite, chert, evaporites); organic (coal).

Sedimentary structures: cross-bedding (current direction), graded bedding (fining upward, turbidites), ripple marks, mudcracks (desiccation), bioturbation, sole marks.

Metamorphic grade indicators: chlorite → biotite → garnet → staurolite → kyanite → sillimanite in pelitic rocks (Barrovian zones); index minerals map metamorphic grade.

Metamorphic rock types: slate (low-grade shale), phyllite, schist, gneiss (high-grade banding), marble (from limestone), quartzite (from sandstone), hornfels (contact metamorphism), eclogite (high P).

Metamorphic facies: zeolite, greenschist, amphibolite, granulite (increasing T), blueschist (high P, low T, subduction), eclogite (very high P); facies reflect P-T conditions.

Fault classification by slip: normal (extension, hanging wall down), reverse/thrust (compression, hanging wall up), strike-slip (lateral, dextral/sinistral); dip-slip vs oblique.

Fold geometry: anticline (older rocks in core), syncline (younger in core); plunging folds, recumbent folds, isoclinal folds; axial plane, hinge line, limb, and fold axis are key terms.

Stress and strain: principal stresses σ1>σ2>σ3; normal faults form with vertical σ1, thrust faults with horizontal σ1, strike-slip with horizontal σ1 and σ3.

Plate tectonics: divergent boundaries (mid-ocean ridges, rift valleys), convergent (subduction zones, island arcs, collision orogens), transform (strike-slip, e.g. San Andreas).

Seafloor spreading: new oceanic crust forms at ridges, magnetic striping records reversals, ages increase away from ridge; Vine–Matthews hypothesis.

Unconformities: angular (tilted beds overlain by flat-lying), nonconformity (sedimentary over igneous/metamorphic), disconformity (erosion surface between parallel beds).

Structural measurement conventions: strike (compass direction of horizontal line on bedding plane), dip (angle and direction of steepest descent), use of Brunton compass and stereonet.

Fold and fault recognition in the field: repetition or omission of strata, drag folds, slickensides, fault breccia, gouge, and offset of marker beds.

Stratigraphic principles: superposition, original horizontality, lateral continuity, cross-cutting relationships, inclusions, faunal succession - used to establish relative ages.

Geological time scale eras: Archaean, Proterozoic (Precambrian), Palaeozoic, Mesozoic, Cenozoic; periods and epochs dated by radiometric methods (U-Pb, K-Ar, Rb-Sr).

Indian stratigraphy: Archaean gneisses and greenstone belts (Dharwar), Proterozoic Cuddapah and Vindhyan supergroups, Gondwana coal measures, Deccan Traps, Siwalik molasse.

Gondwana sequence: Talchir (tillite), Barakar (coal), Kamthi, and plant fossils (Glossopteris); represents Permian–Triassic continental basins.

Deccan Traps: Late Cretaceous–Palaeocene flood basalts, ~65 Ma, related to Réunion hotspot; intertrappean beds yield dinosaur and plant fossils.

Himalayan stratigraphy: Outer (Siwalik), Lesser, Higher Himalaya; Tethyan sequence; Main Boundary Thrust (MBT) and Main Central Thrust (MCT) separate tectonic zones.

Vindhyan Supergroup: largely undeformed Proterozoic sandstone, shale, limestone; famous for diamond-bearing conglomerates (Panna) and stromatolites.

Cuddapah Supergroup: Proterozoic quartzite, shale, limestone, with unconformable relationship over Archaean basement; important for base-metal and uranium deposits.

Fossil preservation types: permineralization, replacement, mould and cast, carbonization, amber entrapment, trace fossils (ichnofossils), and unaltered hard parts.

Index fossils are geographically widespread, short-lived, and abundant: graptolites, trilobites, ammonites, conodonts, foraminifera - used for biostratigraphic correlation.

Major invertebrate groups: brachiopods, bivalves, gastropods, cephalopods (ammonites, belemnites), corals, echinoderms (crinoids), trilobites, graptolites.

Vertebrate evolution: fishes → amphibians → reptiles → dinosaurs → birds and mammals; therapsid reptiles are ancestral to mammals; Archaeopteryx links reptiles and birds.

Mass extinctions: end-Ordovician, Late Devonian, end-Permian (largest, ~90% species), end-Triassic, end-Cretaceous (K-Pg, asteroid impact, dinosaurs).

Geological time divisions: Hadean, Archaean, Proterozoic (Precambrian ~88% of Earth history), then Palaeozoic, Mesozoic, Cenozoic eras; epochs of Cenozoic: Palaeocene to Holocene.

Stromatolites are layered structures built by cyanobacteria, abundant in Precambrian; they record early life and are used for palaeoenvironmental interpretation.

Trace fossils (e.g. Cruziana, Skolithos, Ophiomorpha) indicate behaviour and environment, not the organism itself; useful where body fossils are absent.

Ore deposit types: magmatic (chromite, Ni-Cu sulphide), hydrothermal (veins, porphyry Cu), sedimentary (banded iron formation, phosphorite), placer (gold, diamond), residual (bauxite, laterite).

India's major mineral belts: Jharia and Raniganj coalfields, Bailadila and Kudremukh iron ore, Kolar gold field, Panna diamonds, Rajasthan zinc-lead (Zawar), Khetri copper.

Bauxite forms by lateritic weathering of aluminous rocks; India's deposits in Odisha, Jharkhand, Gujarat; aluminium ore processed to alumina then aluminium.

Manganese, chromite, and mica: India is a leading producer; mica (muscovite) from Jharkhand/Bihar; chromite from Sukinda (Odisha).

Petroleum system elements: source rock (organic-rich shale), reservoir (porous sandstone/carbonate), seal (impermeable shale/evaporite), trap (structural/stratigraphic), and migration pathway.

Coal rank increases with burial: peat → lignite → sub-bituminous → bituminous → anthracite; rank reflects increasing carbon and calorific value.

Mineral exploration methods: geological mapping, geochemical sampling (soil, stream sediment), geophysical surveys (gravity, magnetic, seismic, resistivity), and drilling.

Ore reserve estimation uses grade–tonnage relationships, cut-off grade, and resource classification (measured, indicated, inferred).

Groundwater occurrence: zone of aeration, capillary fringe, zone of saturation; water table is the upper surface of saturation; aquifer types: unconfined, confined, perched.

Darcy's law: Q = K·A·(dh/dL), where Q is discharge, K hydraulic conductivity, A cross-sectional area, dh/dL hydraulic gradient; flow is proportional to gradient.

Porosity and permeability: porosity is void fraction; permeability is ability to transmit fluid; well-sorted sand has high porosity and permeability, clay high porosity but low permeability.

Engineering geology: rock mass classification (RMR, Q-system), slope stability (factor of safety), bearing capacity, and foundation problems in expansive clay or karst terrain.

Landslide controls: slope angle, rock/soil strength, water content, vegetation, and undercutting; mitigation includes drainage, retaining structures, and slope reduction.

Seismic hazard: earthquake magnitude (Richter, moment magnitude) vs intensity (Mercalli); seismic zonation of India (Zones II–V) guides building codes.

Environmental geology: contamination pathways in groundwater, leachate from landfills, acid mine drainage, and remediation by pump-and-treat or permeable reactive barriers.

Tunnelling and excavation: rock quality designation (RQD) from drill core, stand-up time, and support systems depend on jointing and weathering.

Field mapping: use topographic base maps, compass-clinometer (Brunton), GPS, hand lens (10x), hardness kit, dilute HCl, and field notebook with sketches and measurements.

Strike and dip measurement: strike is the compass direction of the horizontal line on the bedding plane; dip is the angle and direction of maximum inclination, measured perpendicular to strike.

Geological map interpretation: outcrop pattern depends on dip and topography - V-shape points upstream for beds dipping upstream; contour and bed intersections reveal attitude.

Stereographic projection (equal-area net): plotting planes as great circles and lines as points; used to analyse fold axes, fault planes, and joint sets.

Rock description in the field: colour, grain size, texture, mineralogy, weathering, and structure; record contacts, bedding, and structural measurements systematically.

Sampling: representative, uncontaminated, labelled with location and orientation; oriented samples for palaeomagnetic or structural analysis.

Cross-section construction: project surface geology to depth using dip angles; honour stratigraphic thickness and structural continuity; check with borehole data.

Practical identification: use streak plate, acid test, hardness, cleavage, and cleavage angle to distinguish calcite (3 cleavages, effervesces) from dolomite (weak effervescence in dilute acid).