CHSE Odisha Elective Geology cheat sheet

Mohs hardness scale (1–10): talc, gypsum, calcite, fluorite, apatite, orthoclase, quartz, topaz, corundum, diamond; a mineral scratches any mineral of lower number.

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.

Silicate classification by SiO4 polymerization: nesosilicate (isolated, e.g. olivine) → sorosilicate → cyclosilicate → inosilicate single chain (pyroxene) and double chain (amphibole) → phyllosilicate (mica, clay) → tectosilicate (quartz, feldspar).

Igneous rock naming: plutonic vs volcanic texture plus mineralogy; granite = quartz + alkali feldspar + plagioclase + mica; basalt = calcic plagioclase + pyroxene + olivine; grain size reflects cooling rate, not composition alone.

Magma series: tholeiitic (low K, ocean floor), calc-alkaline (subduction arcs), alkaline (within-plate); SiO2 increase raises viscosity and lowers melting temperature.

Sedimentary rock classification: clastic by grain size (rudite >2 mm, arenite 0.0625–2 mm, lutite <0.0625 mm); chemical/biochemical by composition (limestone, dolomite, chert, evaporite); maturity = textural plus mineralogical.

Metamorphic facies sequence with rising grade: zeolite → greenschist → amphibolite → granulite; blueschist marks high-P low-T subduction; eclogite marks very high P; index minerals (chlorite, biotite, garnet, staurolite, kyanite, sillimanite) map isograds.

Stratigraphic principles: superposition, original horizontality, lateral continuity, cross-cutting relationships, inclusions, and faunal succession; unconformities are angular, nonconformity, or disconformity.

Structural geology: strike and dip describe planar orientation; anticline (oldest core) vs syncline (youngest core); normal fault = extension, reverse/thrust = compression, strike-slip = lateral shear; fold axis, axial plane, and plunge complete the description.

Plate tectonics: divergent boundary → new oceanic crust and normal faults; convergent ocean–ocean → island arc; ocean–continent → Andean arc; continent–continent → collision and thrust belts; transform → strike-slip.

Earthquake magnitude scales: Richter is local magnitude (logarithmic amplitude); moment magnitude Mw uses seismic moment and does not saturate for great earthquakes; intensity (Mercalli) measures observed damage.

Seismic wave order of arrival: P (compressional, fastest, travels through solids and fluids) → S (shear, solids only) → surface waves (Love, Rayleigh; slowest, most damaging).

Wegener's continental drift evidence: fit of coastlines, matching fossils (Glossopteris), glacial striations, and paleoclimatic belts; seafloor spreading and magnetic striping later supplied the mechanism.

Weathering and soils: physical (frost, exfoliation, salt) vs chemical (hydrolysis, oxidation, carbonation); laterite forms in tropical high-rainfall leaching; bauxite is a residual lateritic ore of aluminium.

Ore genesis classes: magmatic segregation (chromite, magnetite), hydrothermal veins (gold, base metals), porphyry copper, skarn, sedimentary (banded iron formation, phosphorite), placer (gold, diamond, monazite), residual (bauxite).

Coal rank series with increasing maturity: peat → lignite → sub-bituminous → bituminous → anthracite; rank rises with carbon content and calorific value while volatile matter and moisture fall.

Hydrocarbon trap elements: source rock (organic-rich, mature), reservoir (porous, permeable), seal (impermeable cap), trap (structural or stratigraphic), and timing of migration; anticlinal trap is the classic structural type.

Groundwater and geomorphology: porosity vs permeability; water table, aquifer, aquiclude; drainage patterns - dendritic (uniform rock), trellis (folded strata), radial (dome/volcano), rectangular (jointed rock).