CHSE Odisha Elective Geology flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Mohs hardness scale

A relative ten-point scale from talc (1) to diamond (10) in which each mineral scratches those below it; used for rapid field identification of unknown minerals.

Cleavage in minerals

The tendency of a mineral to break along planes of weak atomic bonding, producing flat shiny surfaces; described by number of directions and angle, as in mica (one) or calcite (three).

Bowen's reaction series

An experimental sequence showing that mafic minerals such as olivine crystallize at high temperature and felsic minerals such as quartz at low temperature, explaining igneous mineral assemblages.

Tectosilicate structure

A silicate framework in which every SiO4 tetrahedron shares all four oxygens, giving a three-dimensional network; quartz and feldspar are the common examples.

Phyllosilicate structure

A sheet silicate in which tetrahedra share three oxygens, forming layers with perfect basal cleavage; micas, chlorite, and clay minerals belong here.

Plutonic versus volcanic texture

Plutonic rocks cool slowly at depth and are coarse-grained (phaneritic); volcanic rocks cool quickly at the surface and are fine-grained (aphanitic) or glassy.

Granite composition

A coarse-grained felsic plutonic rock of quartz, alkali feldspar, and plagioclase with biotite or muscovite; silica content is high and colour index low.

Basalt composition

A fine-grained mafic volcanic rock dominated by calcic plagioclase and pyroxene with some olivine; it is dark, dense, silica-poor, and forms most oceanic crust.

Clastic grain-size classes

Rudite exceeds 2 mm, arenite (sand) is 0.0625 to 2 mm, and lutite (silt and clay) is below 0.0625 mm; these classes name clastic sedimentary rocks.

Metamorphic facies

A set of mineral assemblages that form under a defined pressure-temperature range; the sequence zeolite, greenschist, amphibolite, and granulite records increasing grade.

Index minerals and isograds

Index minerals such as chlorite, biotite, garnet, staurolite, kyanite, and sillimanite mark progressive metamorphism; an isograd is the map line of their first appearance.

Foliation

A planar fabric in metamorphic rock produced by aligned platy or elongate minerals under directed stress; slate, schist, and gneiss are named from its development.

Law of superposition

In an undisturbed sequence of layered sedimentary rocks, each layer is younger than the one below it and older than the one above it.

Angular unconformity

An erosion surface on which tilted or folded older strata are overlain by younger, nearly horizontal layers, recording deformation followed by erosion and renewed deposition.

Anticline versus syncline

An anticline is an upward-arching fold with the oldest beds in its core; a syncline is a downward-trough fold with the youngest beds in its core.

Normal fault

A dip-slip fault where the hanging wall moves down relative to the footwall, produced by crustal extension; it commonly forms horst-and-graben terrain.

Reverse and thrust faults

Dip-slip faults where the hanging wall moves up, caused by compression; a thrust is a low-angle reverse fault and shortens the crust in fold-thrust belts.

Strike and dip

Strike is the compass direction of a horizontal line on a bedding plane; dip is the angle of steepest descent measured perpendicular to strike.

Plate boundary types

Divergent boundaries create new crust, convergent boundaries destroy or collide crust, and transform boundaries slide laterally; each produces a characteristic earthquake and volcano style.

Seafloor magnetic striping

Symmetrical bands of normal and reversed magnetization on either side of mid-ocean ridges record alternating reversals of Earth's field and support seafloor spreading.

Seismic wave arrival order

P waves arrive first, S waves second, and surface waves last; S waves cannot pass through liquids, which revealed Earth's liquid outer core.

Moment magnitude

A magnitude scale based on seismic moment, combining fault area, slip, and rock rigidity; unlike older scales it does not saturate for very large earthquakes.

Earthquake focus and epicentre

The focus is the point within the Earth where rupture begins; the epicentre is the point on the surface directly above it, where damage is often greatest.

Chemical weathering processes

Hydrolysis alters feldspar to clay, oxidation rusts iron minerals, and carbonation dissolves limestone; warm, wet climates accelerate all three reactions.

Laterite and bauxite

Intense tropical leaching removes silica and alkalis, leaving residual iron and aluminium oxides; bauxite, the aluminium ore, forms this way.

Hydrothermal ore deposits

Metal-bearing hot fluids precipitate sulphides and native metals in fractures and veins as they cool or react with wall rock; gold and base-metal veins are typical.

Placer deposits

Dense, resistant minerals such as gold, cassiterite, diamond, and monazite are concentrated by flowing water in stream and beach gravels.

Coal rank series

Peat, lignite, sub-bituminous, bituminous, and anthracite record increasing maturity; carbon and calorific value rise while moisture and volatile matter fall.

Petroleum trap elements

A working petroleum system needs a mature source rock, a porous reservoir, an impermeable seal, a trap geometry, and favourable migration timing.

Porosity versus permeability

Porosity is the fraction of void space in rock; permeability is the ability of a fluid to flow through it, so clay may be porous but nearly impermeable.

Drainage patterns

Dendritic patterns develop on uniform rock, trellis patterns on folded strata, radial patterns around domes or volcanoes, and rectangular patterns on jointed rock.

Metamorphic grade indicators

Grade is estimated from mineral assemblage, texture, and foliation intensity; slate, phyllite, schist, and gneiss record progressively higher temperature and pressure.