Maharashtra HSC Geology (MSBSHSE) cheat sheet

Nebular hypothesis (Kant-Laplace, refined by Chamberlin-Moulton planetesimal and Safronov accretion models): solar nebula condenses, planetesimals accrete, differentiation by density follows.

Earth's layered interior by composition: crust (oceanic ~5-10 km basaltic, continental ~30-70 km granitic), mantle (to ~2900 km, peridotitic), core (Fe-Ni, outer liquid, inner solid).

Seismic discontinuities: Mohorovičić (crust-mantle), Gutenberg (mantle-outer core, ~2900 km), Lehmann (outer-inner core, ~5150 km); Low-velocity zone in upper mantle = asthenosphere.

P and S wave behaviour: P (compressional) travel through solids, liquids, gases; S (shear) cannot pass liquids, which proves a liquid outer core and the S-wave shadow beyond 103°.

Isostasy: Airy model = variable crustal root, Pratt model = variable density; continental crust floats higher because of lower density, not greater thickness alone.

Geological time scale order: Hadean, Archaean, Proterozoic (together Precambrian), then Palaeozoic (Cambrian to Permian), Mesozoic (Triassic, Jurassic, Cretaceous), Cenozoic (Palaeogene, Neogene, Quaternary).

Radiometric dating: decay constant λ, N = N0e^(-λt); half-life t½ = 0.693/λ. Suitable pairs: U-Pb zircon, K-Ar and Ar-Ar, Rb-Sr, Sm-Nd, C-14 (short range, ~5730 yr half-life).

Relative age principles: superposition, original horizontality, lateral continuity, cross-cutting relationships, inclusions, faunal succession; unconformities are angular, non-conformity, or disconformity.

Earth's origin of life and atmosphere: earliest life ~3.5 Ga (stromatolites), banded iron formations mark Great Oxidation Event ~2.4 Ga; Precambrian shields of India (Dharwar, Singhbhum, Aravalli, Bundelkhand) are Archaean nuclei.

Six crystal systems and minimum symmetry: isometric (4 threefold axes), tetragonal (one fourfold), hexagonal (one sixfold or threefold), orthorhombic (three twofold), monoclinic (one twofold), triclinic (only centre).

Crystallographic axes: isometric a1=a2=a3 at 90°; tetragonal a1=a2≠c at 90°; hexagonal four axes (a1=a2=a3 at 120°, c at 90°); orthorhombic a≠b≠c at 90°; monoclinic a≠b≠c with β≠90°; triclinic all unequal and oblique.

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.

Cleavage is controlled by weakest atomic planes and repeated; fracture is irregular (conchoidal in quartz, hackly in metals). Specific gravity, streak, lustre, colour, and magnetism complete identification.

Silicate building block: SiO4 tetrahedron; Si-O bond is ~50% ionic, so tetrahedra polymerise by sharing oxygens. Pauling's rules govern cation coordination and charge balance.

Silicate classes by polymerisation: nesosilicates (isolated, olivine, garnet), sorosilicates (double tetrahedra, epidote), cyclosilicates (rings, beryl, tourmaline), inosilicates (single chain pyroxene, double chain amphibole), phyllosilicates (sheets, mica, clay), tectosilicates (framework, quartz, feldspar).

Si:O ratios fall with polymerisation: olivine 1:4, pyroxene 1:3, amphibole 4:11, mica 2:5, quartz 1:2; higher polymerisation gives lower density and higher viscosity of melts.

Bowen's reaction series: discontinuous branch olivine → pyroxene → amphibole → biotite; continuous branch Ca-plagioclase → Na-plagioclase; both converge on orthoclase then muscovite then quartz at lowest temperature.

Polymorphism and isomorphism: same composition different structure (calcite-aragonite, quartz-tridymite-cristobalite, diamond-graphite); isomorphic minerals share structure with substituting ions (olivine series forsterite-fayalite).

Magma generation settings: decompression melting at mid-ocean ridges and rifts, flux melting by water release above subduction zones, and heat addition at hotspots and continental collision; geothermal gradient and solidus intersect.

Magma types and silica: ultramafic (komatiite, <45% SiO2), mafic (basalt/gabbro, 45-52%), intermediate (andesite/diorite, 52-63%), felsic (rhyolite/granite, >63%); silica increase raises viscosity and lowers temperature.

Classification by mineralogy and mode: QAPF (Streckeisen) for plutonic rocks using quartz, alkali feldspar, plagioclase, feldspathoid; TAS diagram for volcanic rocks using total alkalis versus silica.

Colour index (mafic mineral percentage): leucocratic <35, mesocratic 35-65, melanocratic >65; ultramafic rocks >90% mafic minerals.

Texture = grain size, shape, and arrangement: phaneritic (coarse, plutonic), aphanitic (fine, volcanic), porphyritic (two-stage cooling), glassy (obsidian), vesicular (pumice, scoria), pyroclastic (tuff, agglomerate).

Special textures: ophitic (plagioclase laths enclosed by pyroxene, dolerite), poikilitic, intergrowth (graphic granite, granophyric), reaction rims and corona, pegmatitic (>3 cm grains), amygdaloidal (filled vesicles).

Crystallisation sequence follows Bowen's series; fractional crystallisation enriches residual melt in silica, alkalis, and incompatible elements; assimilation and magma mixing modify composition.

Volcanic landforms and products: shield (basaltic, low viscosity), composite/strato-volcano (andesitic, explosive), cinder cone, lava plateau (Deccan Traps flood basalt), caldera; pyroclastic fall, flow, and surge deposits.

Deccan Traps of Maharashtra: ~66 Ma, linked to Réunion hotspot, three lava formations (Jawhar, Lonavala, Poladpur) and Wai Subgroup, mostly tholeiitic basalt with intertrappean beds.

Weathering and transport produce sediment; deposition by water, wind, ice, or gravity; diagenesis (compaction, cementation, recrystallisation) converts sediment to rock.

Clastic grain-size scale: gravel >2 mm, sand 2-0.0625 mm, silt 0.0625-0.004 mm, clay <0.004 mm; sorting and roundness record transport distance and energy.

Maturity: textural maturity = low clay, good sorting, rounded grains; mineralogical maturity = high quartz, low feldspar and unstable minerals.

Sedimentary structures as palaeoenvironment indicators: cross-bedding (current direction), graded bedding (turbidites), ripple marks (wave vs current), mud cracks (desiccation), bioturbation, sole marks.

Carbonate classification: Folk (allochemical vs orthochemical components) and Dunham (mudstone, wackestone, packstone, grainstone, boundstone, crystalline); limestone, dolomite, chert, evaporites are chemical/biochemical.

Metamorphism types: contact/thermal (around intrusions, hornfels, non-foliated), regional/dynamothermal (orogenic belts, foliated), dynamic/cataclastic (fault zones), burial, and hydrothermal/metasomatic.

Metamorphic grades and index minerals: chlorite → biotite → garnet → staurolite → kyanite → sillimanite; zones mapped by isograds, facies include greenschist, amphibolite, granulite, eclogite.

Foliated rocks by increasing grade: slate → phyllite → schist → gneiss; non-foliated: quartzite (from sandstone), marble (limestone), hornfels, amphibolite.

Metamorphic textures and concepts: porphyroblast, poikiloblast, augen, mylonite, schistosity, gneissose banding; protolith, metasomatism, and P-T-t paths; anatexis produces migmatite.

Strike is the compass direction of a horizontal line on a bedding plane; dip is the angle of steepest descent measured perpendicular to strike, with dip direction = strike + 90°.

Folds: anticline (older rocks in core), syncline (younger in core), monocline; elements are limb, hinge line, axial plane, crest, and trough; plunging folds give V-shaped outcrop patterns.

Fold classification: symmetrical, asymmetrical, overturned, recumbent, isoclinal; parallel/concentric vs similar folds; drag folds and minor structures indicate vergence.

Faults by movement: normal (hanging wall down, extension), reverse/thrust (hanging wall up, compression), strike-slip (dextral/sinistral); oblique-slip combines both.

Fault recognition: displaced beds, slickensides, drag folds, gouge and breccia, mylonite, fault scarps, springs and offset streams; hanging wall and footwall defined on the inclined fault plane.

Joints are fractures with no visible displacement; systematic vs nonsystematic, columnar, sheet, and shear joints; they control groundwater flow, quarrying, and slope stability.

Plate tectonics: lithospheric plates move over the asthenosphere; divergent (ridges, rifts), convergent (subduction, collision), and transform boundaries; Wilson cycle describes ocean opening and closing.

Evidence for plate tectonics: sea-floor magnetic stripes, palaeomagnetic polar wander, matching continental margins and fossils (Gondwana), earthquake and volcano belts, age of ocean floor, and hotspot tracks.

Indian plate setting: northward convergence with Eurasia at ~5 cm/yr, Himalayan collision and Main Boundary/Main Central/Main Frontal Thrusts, Narmada-Son and Tapti lineaments, Koyna-Warna seismic zone in Maharashtra.

Fossil preservation types: petrifaction, mould and cast, impression, carbonisation, amber, permineralisation, trace fossils (ichnofossils), and coprolites; index fossils are short-ranging and wide-spread.

Key invertebrate groups: trilobites (Cambrian), graptolites (Ordovician-Silurian), brachiopods, ammonites (Jurassic-Cretaceous), corals, echinoids, and bivalves; each has a stratigraphic range.

Vertebrate and plant fossils: dinosaurs (Mesozoic), Siwalik mammals (Miocene-Pliocene), Glossopteris and Gangamopteris flora of Gondwana coal measures, and marine reptiles.

Geological Survey of India stratigraphic succession: Archaean Dharwar and Singhbhum, Proterozoic Cuddapah and Vindhyan supergroups, Palaeozoic Gondwana, Mesozoic Deccan Traps and Bagh beds, Cenozoic Siwalik and Assam.

Gondwana Supergroup: Talchir (tillite, glacial), Barakar (coal), Kamthi, and Maleri; plant fossils and coal seams; Damodar, Godavari, and Satpura basins.

Deccan Traps stratigraphy: three formations (Jawhar, Lonavala, Poladpur) with intertrappean beds yielding dinosaur eggs (Kheda) and freshwater fossils; Cretaceous-Palaeogene boundary interval.

Siwalik Group: Lower, Middle, and Upper Siwalik; vertebrate fossils including Ramapithecus and Sivapithecus; foreland basin of the Himalayan orogen.

Cretaceous-Palaeogene (K-Pg) boundary: iridium anomaly, shocked quartz, and microtektites support the Chicxulub impact hypothesis; Deccan volcanism is an alternative or contributing cause.

Stratigraphic principles and correlation: lithostratigraphy, biostratigraphy, chronostratigraphy; unconformities and type sections; the standard geological time scale with absolute ages in Ma.

Ore genesis classes: magmatic segregation (chromite, magnetite), hydrothermal veins (gold, base metals), porphyry (copper), skarn, VMS and SEDEX (zinc-lead), laterite (bauxite), placer, and evaporite deposits.

Maharashtra manganese belt: Nagpur-Bhandara region (Balaghat belt extension), Gondite and kodurite rocks; manganese ores with pyrolusite, psilomelane, and manganite.

Bauxite in Maharashtra: laterite-capped plateaus of Ratnagiri, Sindhudurg, Raigad, and Kolhapur, derived from Deccan basalt weathering; alumina-rich laterite ore.

Coal: Wardha valley coalfield (Wardha-Godavari basin), Kamptee, Umrer, and Wani; Gondwana coal of Permian age, high ash content; Tertiary lignite in Ratnagiri and Sindhudurg.

Iron ore and other minerals: iron ore in Chandrapur and Gadchiroli (metasedimentary), limestone for cement in Yavatmal and Chandrapur, dolomite, kyanite, sillimanite, and graphite in eastern Vidarbha.

Building and decorative stones: Deccan basalt as aggregate and dimension stone, laterite blocks, and Pune-Chakan limestone; sand as a minor mineral regulated by state permits.

Mineral sands and gemstones: ilmenite, rutile, monazite, and zircon in Konkan beach sands; zeolites and agate in Deccan Traps (Nashik, Jalgaon); fluorite and barytes occurrences.

Mineral economics: ore grade, cut-off grade, reserve vs resource (UNFC), beneficiation, and mine waste; national mineral policy and state royalty/lease framework; sustainable mining and mine closure.

Petroleum and groundwater energy links: Mumbai Offshore (Bombay High) oil and gas, Krishna-Godavari basin gas; coal-bed methane and shale prospects; geothermal springs at Unhala and Ganeshpuri.

Engineering geology site investigation: geological mapping, boreholes, SPT, RQD, core logging, and geophysical methods; rock mass classification by RMR and Q-system guides support design.

Soil and rock properties: porosity, permeability, compressibility, shear strength (Mohr-Coulomb c and φ), Atterberg limits, and rock strength (UCS); weathering grade affects foundation bearing capacity.

Slope stability: factor of safety = resisting/shearing forces; landslides triggered by rainfall, undercutting, and deforestation; mitigation by drainage, benching, retaining walls, and vegetation.

Groundwater occurrence: porosity, permeability, and specific yield; aquifers unconfined and confined; water table, potentiometric surface, and perched water table; Deccan basalt aquifers in weathered and vesicular zones.

Darcy's law: Q = K i A; transmissivity T = K b; storativity; pumping test analysis by Theis and Cooper-Jacob methods; well yield, drawdown, and specific capacity.

Groundwater quality: TDS, hardness, chloride, fluoride, nitrate, and arsenic; WHO/BIS drinking water limits; contamination by seawater intrusion in coastal Konkan and by agricultural runoff.

Environmental geology issues: soil erosion, desertification, mine spoil, fly ash and industrial effluent, solid waste siting, and air pollution; environmental impact assessment and mitigation.

Natural hazards of Maharashtra: earthquakes (Koyna-Warna reservoir-triggered seismicity), floods (Krishna, Godavari), droughts, and landslides in the Western Ghats; early warning and land-use planning.

Remote sensing and GIS in applied geology: satellite imagery, DEM, and thematic maps for groundwater potential, land-use, hazard zonation, and mineral exploration targeting.