← Geology syllabus

EnglandGeology

Rock-forming processes

6 dot points across 6 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

What shapes do igneous bodies take underground and at the surface, and how do we use them to read relative age?

Igneous intrusions and volcanic forms: concordant intrusions (sills and laccoliths) versus discordant intrusions (dykes, batholiths and stocks); chilled margins, and baked margins and contact aureoles around intrusions, as way-up and relative-age evidence; cross-cutting relationships; and volcanic forms (shield volcanoes, stratovolcanoes or composite cones, cinder cones, calderas and lava plateaux).
A focused answer to the Eduqas Geology statement on igneous bodies. Covers concordant sills and laccoliths versus discordant dykes, batholiths and stocks, chilled and baked margins and aureoles as way-up and relative-age evidence, cross-cutting relationships, and the main volcanic forms (shield, stratovolcano, cinder cone, caldera, lava plateau).
14 min answer →

How are igneous rocks classified by composition and texture, and what does texture tell us about how a magma cooled?

Igneous rock classification and textures: the classification of igneous rocks by silica content and composition (ultramafic peridotite, mafic basalt and gabbro, intermediate andesite and diorite, felsic rhyolite and granite) and by grain size and cooling rate (glassy, aphanitic, phaneritic, porphyritic, vesicular and pyroclastic textures); and the relationship between cooling rate and crystal size.
A focused answer to the Eduqas Geology statement on igneous rock classification. Covers the compositional series from ultramafic peridotite through mafic basalt and gabbro and intermediate andesite and diorite to felsic rhyolite and granite, the link between cooling rate and crystal size, and the named textures (glassy, aphanitic, phaneritic, porphyritic, vesicular and pyroclastic).
13 min answer →

Why do minerals crystallise from a magma in a fixed order, and how does that evolve the magma from mafic to felsic?

Magma differentiation and Bowen's reaction series: the order of crystallisation of silicate minerals from a cooling magma (the discontinuous ferromagnesian branch olivine to pyroxene to amphibole to biotite, and the continuous plagioclase branch from calcium-rich to sodium-rich, then potassium feldspar, muscovite and quartz); fractional crystallisation and partial melting; and how differentiation evolves a magma from mafic to felsic.
A focused answer to the Eduqas Geology statement on magma differentiation. Covers Bowen's reaction series (the discontinuous ferromagnesian branch and the continuous plagioclase branch), fractional crystallisation and partial melting, the order of crystallisation, and how differentiation evolves a magma from mafic to felsic compositions.
14 min answer →

How do heat and pressure transform existing rocks, and how do we read metamorphic grade and facies?

Metamorphism, grade and facies: contact (thermal) metamorphism producing hornfels within an aureole versus regional metamorphism producing foliated rocks; the agents of metamorphism (heat, pressure and chemically active fluids); metamorphic grade and the prograde sequence from mudstone (slate, phyllite, schist, gneiss) with index minerals (chlorite, biotite, garnet, kyanite, sillimanite); foliated rocks (slate, schist, gneiss) versus non-foliated rocks (marble from limestone, quartzite from sandstone); protoliths; and metamorphic facies in outline.
A focused answer to the Eduqas Geology statement on metamorphism. Covers contact versus regional metamorphism, the agents (heat, pressure, fluids), metamorphic grade and the mudstone prograde sequence (slate, phyllite, schist, gneiss) with index minerals, foliated versus non-foliated rocks (marble, quartzite), protoliths, and metamorphic facies in outline.
14 min answer →

How are sedimentary rocks classified, and what do their structures reveal about where they formed?

Sedimentary rocks and depositional environments: the classification of clastic rocks by grain size (conglomerate and breccia, sandstone including arkose, greywacke and orthoquartzite, siltstone, mudstone and shale) and of chemical and biogenic rocks (limestone including oolitic, micritic and fossiliferous, chalk, the evaporites rock salt and gypsum, and coal); sedimentary structures (cross-bedding, graded bedding, ripple marks, desiccation cracks) as way-up and environment indicators; depositional environments (fluvial, deltaic, shallow marine, deep marine, desert); and diagenesis and lithification.
A focused answer to the Eduqas Geology statement on sedimentary rocks. Covers clastic classification (conglomerate to mudstone, with arkose, greywacke and orthoquartzite), chemical and biogenic rocks (limestones, chalk, evaporites, coal), sedimentary structures as way-up and environment indicators, depositional environments, and diagenesis and lithification.
15 min answer →

How do rocks break down at the surface, and how does transport sort and shape the sediment that results?

Weathering, erosion and sediment transport: physical weathering (freeze-thaw and exfoliation), chemical weathering (hydrolysis of feldspar to clay, carbonation of limestone, oxidation) and biological weathering; the distinction between weathering and erosion; transport by traction, saltation, suspension and solution, and how transport rounds and sorts grains to determine the maturity of a sediment.
A focused answer to the Eduqas Geology statement on surface processes. Covers physical weathering (freeze-thaw, exfoliation), chemical weathering (hydrolysis of feldspar to clay, carbonation, oxidation), biological weathering, the weathering versus erosion distinction, and transport (traction, saltation, suspension, solution) with rounding, sorting and maturity.
14 min answer →