CHSE Odisha Elective Geology key terms

A naturally occurring, inorganic solid with a definite chemical composition and an ordered internal atomic arrangement, giving it characteristic physical properties such as hardness, cleavage and crystal form.

A coherent aggregate of one or more minerals, or of glassy or organic material, forming a significant part of the Earth's crust and classified as igneous, sedimentary or metamorphic by origin.

A relative scale from 1 (talc) to 10 (diamond) ranking minerals by their resistance to scratching; a mineral scratches those below its number and is scratched by those above.

The tendency of a mineral to break along flat planes determined by weak bonding directions in its atomic structure, described by the number of planes and their angles.

The way a mineral breaks when it does not split along regular cleavage planes, producing surfaces that may be conchoidal, uneven, hackly or splintery.

One of seven geometric classes (cubic, tetragonal, orthorhombic, monoclinic, triclinic, hexagonal and trigonal) defined by the lengths and mutual angles of the unit-cell axes of a mineral.

The arrangement of silicon-oxygen tetrahedra (SiO4) in a mineral, ranging from isolated tetrahedra through chains, sheets and frameworks; it controls most rock-forming mineral properties.

The sequence in which silicate minerals crystallise from a cooling magma, from olivine and calcium-rich plagioclase at high temperature to quartz, muscovite and potassium feldspar at low temperature.

A rock formed by the cooling and solidification of magma or lava, classified by silica content, mineral composition and grain size as intrusive (coarse) or extrusive (fine).

The process by which a single parent magma produces melts of different composition through crystal settling, partial melting, assimilation of wall rock or mixing with other magmas.

Rock formed at or near the Earth's surface from compacted and cemented sediment, or by chemical precipitation or organic accumulation, typically showing layers called beds.

The in-place breakdown of rocks and minerals by physical processes such as freeze-thaw and by chemical processes such as hydrolysis and oxidation, producing regolith and dissolved ions.

The removal and transport of weathered material by agents such as running water, wind, ice and gravity, which together with weathering supplies sediment to depositional basins.

The low-temperature changes that convert loose sediment into sedimentary rock after deposition, including compaction, cementation, recrystallisation and replacement of grains.

A feature preserved in sedimentary rock, such as bedding, cross-bedding, graded bedding, ripple marks or mud cracks, that records conditions during deposition and helps interpret the environment.

A specific setting where sediment accumulates, such as a river channel, delta, beach, reef, deep sea or glacial margin, recognised from its characteristic sediments and structures.

Rock whose mineral composition or texture has been changed in the solid state by heat, pressure or chemically active fluids, commonly developing foliation or porphyroblastic textures.

The solid-state recrystallisation of a rock in response to changed temperature, pressure or fluid composition, ranging from low-grade burial changes to high-grade regional metamorphism.

A planar fabric in metamorphic rock produced by the parallel alignment of platy or elongate minerals under directed stress, seen as slaty cleavage, schistosity or gneissic banding.

A set of mineral assemblages that form under a restricted range of pressure and temperature, used to map metamorphic grade and tectonic setting.

The continuous set of processes by which igneous, sedimentary and metamorphic rocks are transformed into one another through melting, weathering, burial and uplift.

The theory that the lithosphere is divided into rigid plates that move over the asthenosphere, interacting at divergent, convergent and transform boundaries to produce most major geological features.

The process at mid-ocean ridges where new oceanic lithosphere forms from upwelling magma and moves away on either side, recorded by symmetrical magnetic anomaly stripes.

A convergent boundary where one lithospheric plate descends beneath another, generating deep ocean trenches, volcanic arcs, earthquakes and regional metamorphism.

The record of the Earth's past magnetic field preserved in magnetic minerals in rocks, used to document apparent polar wandering, seafloor spreading and reversals of polarity.

A fracture in rock along which displacement has occurred, classified as normal, reverse, strike-slip or oblique according to the sense of relative movement.

A bend in layered rock produced by compressional deformation, described as anticline, syncline or monocline and characterised by its axis, limbs and axial plane.

Two measurements defining the orientation of a planar geological surface: strike is the compass direction of its horizontal line, and dip is its angle of steepest descent.

The shaking of the ground caused by sudden release of stored elastic strain along a fault or by volcanic activity, recorded by seismographs and located from seismic wave arrivals.

Elastic energy travelling through the Earth as body waves (P and S) or surface waves; their arrival times and paths reveal the Earth's internal layering.

The layered arrangement of the Earth into crust, mantle, outer core and inner core, distinguished by composition and by the mechanical boundaries of lithosphere and asthenosphere.

A vent or fissure where magma, ash and gases reach the surface, forming cones, lava plateaus or calderas whose eruption style depends on magma viscosity and gas content.

A vertical section through soil showing horizons O, A, E, B and C, each differing in organic content, colour, texture and degree of weathering of the parent material.

Water held in the pore spaces and fractures of rock and sediment below the water table, moving slowly under gravity and supplying wells and springs.

A body of rock or sediment that stores and transmits groundwater in usable quantities, requiring both porosity to hold water and permeability to allow it to flow.

Porosity is the proportion of void space in a material; permeability is its ability to transmit fluid through connected pores. Both govern how rock holds and yields groundwater.

Any preserved trace of past life, such as skeletal remains, impressions, moulds or tracks, usually found in sedimentary rock and used to date and correlate strata.

A fossil species with a wide geographic range and short geological time span, used to identify and correlate rock strata of the same age across distant regions.

The study of the order, age and correlation of layered rocks, based on superposition, fossil content and lithology, and formalised into groups, formations and members.

The standard division of Earth history into eons, eras, periods and epochs, calibrated by radiometric dating and defined by major changes in fossils and rock records.

Determining the age of rocks or minerals from the measured ratio of a radioactive parent isotope to its stable daughter product, using a known decay constant.