Kerala Plus Two Geology key terms

The principle that the same physical, chemical and biological processes operating today also operated in the geological past, so present-day observations can be used to interpret ancient rocks and structures.

The state of gravitational balance in which the lithosphere floats on the denser asthenosphere, so that thicker or lighter crust rides higher and thinner or denser crust sits lower.

The boundary surface separating the crust from the mantle, marked by an abrupt increase in seismic wave velocity at roughly 5 to 10 km depth beneath oceans and 30 to 70 km beneath continents.

The bending of earthquake waves as they pass from one rock layer into another of different density or elasticity, used to map subsurface boundaries such as the crust-mantle transition.

The in-place breakdown of rocks and minerals by physical, chemical or biological agencies, producing regolith and dissolved ions without transporting the material away.

The removal and transport of weathered rock debris or dissolved load by running water, wind, ice or gravity, a process distinct from the breakdown that produces the debris.

The tendency of a mineral to break along specific planar directions determined by weaker atomic bonding, producing smooth repeated surfaces such as the basal sheets of mica.

A relative ten-point scale ranking minerals from talc (1) to diamond (10) by resistance to scratching, used for quick field identification of unknown specimens.

The ratio of a mineral's mass to the mass of an equal volume of water, a diagnostic property that separates light silicates such as quartz from dense oxides and sulphides.

The fundamental building unit of silicate minerals, a silicon atom surrounded by four oxygen atoms, which links into chains, sheets or frameworks and controls most crustal mineral properties.

The experimentally observed order in which silicate minerals crystallise from a cooling melt, from olivine and calcium-rich plagioclase first to quartz and potassium feldspar last.

The process in which early-formed crystals are separated from the remaining melt, so that the residual liquid becomes progressively enriched in silica and incompatible elements.

Any process that changes a magma's composition after generation, including crystal settling, assimilation of wall rock, magma mixing and volatile loss, producing a range of igneous rock types.

The set of processes, chiefly compaction and cementation, that convert loose sediment into a coherent sedimentary rock after deposition and burial.

A body of rock or sediment distinguished by a particular set of characteristics reflecting its depositional environment, used to reconstruct past settings and lateral changes in strata.

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

The intensity of metamorphism a rock has experienced, expressed by index minerals and mineral assemblages that record increasing temperature and pressure conditions.

A line on a geological map joining points where the first appearance of a particular index mineral marks the same metamorphic grade or reaction boundary.

The two measurements describing an inclined planar surface: strike is the compass direction of its horizontal line, dip is the steepest angle and direction of descent.

Folds in which strata arch upward, with oldest beds in the core, or sag downward, with youngest beds in the core, respectively; both are diagnosed from map patterns and dip directions.

A fracture along which rocks on opposite sides have been displaced, classified as normal, reverse or strike-slip according to the sense of relative movement.

A tabular belt of rock in which strain is concentrated and rocks are deformed by ductile shearing, commonly producing mylonite, foliation and rotated porphyroblasts.

The theory that the lithosphere is divided into rigid plates that move over the asthenosphere, generating earthquakes, volcanoes, mountain belts and ocean basins at their boundaries.

A distinctive assemblage of mafic and ultramafic rocks, including serpentinite, gabbro, sheeted dykes and pillow lavas, interpreted as a fragment of oceanic lithosphere emplaced onto a continent.

A fossil species with wide geographical range and short geological duration, used to correlate strata and assign relative ages across distant sections.

The succession of Late Palaeozoic to Early Mesozoic Gondwana sedimentary rocks of peninsular India, carrying distinctive Glossopteris flora and coal seams, important in Kerala and Indian stratigraphy.

Miocene to Pliocene sedimentary beds of coastal Kerala and southern Tamil Nadu, composed of sandstones, clays and lignite with plant fossils, overlying the Quilon Beds.

A residual weathering product rich in iron and aluminium oxides, formed under intense tropical leaching; it caps many upland surfaces in Kerala and is quarried as building material.

A coarse-grained, orthopyroxene-bearing quartz-feldspar metamorphic or igneous rock forming large parts of the Southern Granulite Terrain, including the Kerala Khondalite Belt margins.

A garnet- and sillimanite-bearing quartz-feldspar granulite, typically graphitic, characteristic of the Kerala Khondalite Belt and indicating high-grade metamorphism of alumina-rich sediments.

A concentration of heavy, durable minerals such as ilmenite, monazite or gold formed by the sorting action of water or wind during sediment transport.

The heavy mineral suite, notably ilmenite, rutile, zircon, monazite and sillimanite, concentrated in the beach placers of the Kerala coast and mined for titanium and rare earths.

A geological formation or body of rock that is sufficiently porous and permeable to store and transmit groundwater in usable quantities through wells and springs.

Porosity is the proportion of void space in a rock; permeability is its capacity to transmit fluid. An aquifer needs both, and high porosity alone does not guarantee yield.

The upper surface of the saturated zone in an unconfined aquifer, fluctuating seasonally with recharge and discharge and controlling the depth required for successful wells.

The skill of reading outcrop patterns, contours, strike and dip symbols and cross-sections to infer the three-dimensional arrangement of rock units beneath the surface.

A vertical record of the rock types, depths and water levels encountered in a drilled hole, used to correlate subsurface units and design wells or foundations.