RBSE SS Geology flashcards

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

Bowen's reaction series

Order of crystallization from cooling magma: olivine, pyroxene, amphibole, biotite (discontinuous) and Ca-plagioclase to Na-plagioclase (continuous), then K-feldspar, muscovite, quartz.

Airy isostasy

Model in which topographic loads are compensated by a low-density crustal root of variable thickness; thicker crust under mountains provides buoyancy.

Barchan dune

Crescent-shaped sand dune with horns pointing downwind, formed where sand supply is limited and wind direction is constant.

Milky quartz hardness

Quartz has Mohs hardness 7 and no cleavage; it scratches glass and steel and is the reference mineral for hardness 7.

Miller indices

Reciprocals of the intercepts a crystal face makes on the crystallographic axes, cleared of fractions; written (hkl) for a face and {hkl} for a form.

Bragg's law

nλ = 2d sinθ, relating X-ray wavelength, lattice d-spacing, and diffraction angle; the basis of X-ray diffraction mineral identification.

Silicate tetrahedron

Fundamental SiO4 unit; silicates are classified by polymerization degree into nesosilicates, sorosilicates, cyclosilicates, inosilicates, phyllosilicates, and tectosilicates.

Felsic magma

Magma with more than 63% SiO2, high viscosity, low temperature, and explosive eruption style; produces rhyolite and granite.

Porphyritic texture

Igneous texture with large crystals (phenocrysts) in a finer groundmass, indicating two-stage cooling: slow at depth then faster near the surface.

Graded bedding

Sedimentary structure in which grain size decreases upward within a bed, typically deposited by a waning turbidity current.

Barrovian zones

Metamorphic zones in pelitic rocks defined by index minerals: chlorite, biotite, garnet, staurolite, kyanite, sillimanite with increasing temperature.

Blueschist facies

High-pressure, low-temperature metamorphic facies formed in subduction zones; characterized by glaucophane, lawsonite, and jadeite.

Normal fault

Dip-slip fault where the hanging wall moves down relative to the footwall, formed by extension; typical of rift zones.

Anticline

Fold with strata arching upward so that older rocks occupy the core; limbs dip away from the axial plane.

Angular unconformity

Erosion surface where tilted or folded strata are overlain by flat-lying younger beds, indicating a period of deformation followed by erosion and deposition.

Seafloor magnetic striping

Symmetrical bands of alternating magnetic polarity on the ocean floor, recording geomagnetic reversals during seafloor spreading.

Principle of superposition

In an undisturbed sequence of sedimentary rocks, the oldest layer is at the bottom and the youngest at the top.

Deccan Traps

Late Cretaceous to Palaeocene flood basalt province of peninsular India, about 65 million years old, linked to the Réunion hotspot.

Gondwana coal measures

Permian continental sequences of peninsular India containing Glossopteris flora and major coal seams, such as the Barakar Formation.

Main Boundary Thrust

Major Himalayan thrust separating the Lesser Himalaya from the Siwalik range to the south, accommodating ongoing collision.

Index fossil

Fossil with wide geographic range, short stratigraphic duration, and abundance, used to correlate and date rock units.

Ammonite

Extinct coiled cephalopod with chambered shell and sutures; an excellent index fossil for the Mesozoic, especially Jurassic and Cretaceous.

End-Permian extinction

The largest mass extinction, about 252 million years ago, eliminating roughly 90% of marine species; linked to Siberian Traps volcanism.

Trace fossil

Ichnofossil recording organism behaviour such as burrows, tracks, or trails; indicates environment and activity rather than the species.

Porphyry copper deposit

Large low-grade copper deposit in felsic intrusive rocks, formed by hydrothermal fluids around a crystallizing magma chamber; often with gold and molybdenum.

Banded iron formation

Precambrian sedimentary rock with alternating iron-rich and silica-rich layers, the main source of iron ore; formed in an oxygen-poor ocean.

Coal rank

Progressive change from peat to lignite, bituminous, and anthracite with increasing burial temperature and pressure, raising carbon content and calorific value.

Petroleum trap

Geological configuration, structural or stratigraphic, that prevents oil and gas from escaping a reservoir; requires seal, reservoir, and closure.

Darcy's law

Groundwater discharge equals hydraulic conductivity times cross-sectional area times hydraulic gradient: Q = K·A·(dh/dL).

Confined aquifer

Aquifer bounded above and below by impermeable layers, so water is under pressure and may rise above the aquifer top in a well.

Seismic zone V

Highest seismic hazard zone of India, covering the Himalayan belt, northeast India, and Kutch; requires the strongest earthquake-resistant design.

Strike and dip

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

Rock quality designation

RQD is the percentage of intact core pieces longer than 10 cm in a drill run, used to classify rock mass quality for engineering.