ERB222 Igneous Petrology and Geochemistry
The Complete Exam Bible · S2 2026ERB222 Overview
- Queensland University of Technology
- S2 2026
- 12 chapters
- Science
What ERB222 is about
ERB222 Igneous Petrology and Geochemistry asks how igneous rocks record the processes that made them.
- Assessed by Examination (written): Theory Exam 25% · Examination (written): Practical Exam 25% + 5 more
- Key terms Primary Magma, Primitive Magma, Solidus, Liquidus
- How to prepare Work in two tracks that mirror the two Week 13 papers.
- Most asked How are the Week 13 exams split between theory and practical?
What you get in the full ERB222 Exam Bible
- 12 chapters, 60 pages — every examinable topic, week by week
- 30 original practice questions, each with a model answer in the Examination format
- 12 worked examples, solved the way ERB222 marks
- 23 computed figures, redrawn from the course’s own numbers
- Exam-morning plan for the Examination (25%) — what to revise last, where marks are lost
Free on this page: assessment table, chapter map, one worked example, key terms, FAQ. The rest is in the full exam bible.
How ERB222 is assessed
| Component | Weight | Format |
|---|---|---|
| Examination (written): Theory Exam | 25% | Two hours in the Week 13 lecture slot; summative theory paper on igneous petrology and geochemistry |
| Examination (written): Practical Exam | 25% | Two hours in the Week 13 practical slot; describe the mineralogy and textures of unknown samples and interpret origin and rock type |
| Field Project (Applied): Field Report | 10% | Individual report of no more than 10 pages integrating field, petrographic and geochemical data; due end of Week 13 |
| Field Project (Applied): Map | 5% | Group field fact map and complete geologic map of the Noosa Headland map area |
| Problem-Solving Task 1: Partial Melting | 10% | Individual; based on Workshops 2 and 3; due 12 August 2026 |
| Problem-Solving Task 2: Fractional Crystallisation | 10% | Individual; based on Workshop 5; due 26 August 2026 on the tasks page, 1 September 2026 on the task sheet |
| Problem-Solving Task 3: Isotopes | 15% | Individual; based on Workshops 10 and 11; due 14 October 2026 |
The seven weighted rows total 100%. The examination is one 50% item split 25% theory and 25% practical, both in Week 13. The Problem-Solving Tasks page says four tasks but lists three, and those three total the published 35%. Problem-Solving Task 2 carries two due dates in the unit materials, 26 August and 1 September 2026; the Canvas assignment governs. No hurdle requirement is stated in the assessment pages available here; check the unit outline on HiQ.
What other students are asking about ERB222
- Where can I find lecture notes or study guides for ERB222 at QUT?
- The ERB222 study guide in AskSia Library covers Igneous Petrology and Geochemistry in 12 chapters, with the assessment table, a chapter-by-chapter topic map, key terms and a worked example, free to read on this page.
- Is there a final exam in ERB222, and how much is it worth?
- Yes. In the offering this AskSia Library guide is built from, Examination (written): Theory Exam carries 25% of the ERB222 mark; the full split is Examination (written): Theory Exam 25%, Examination (written): Practical Exam 25%, Field Project (Applied): Field Report 10%, Field Project (Applied): Map 5%, Problem-Solving Task 1: Partial Melting 10%, Problem-Solving .
- What does ERB222 cover on basalt petrogenesis and mantle melting?
- In AskSia Library's ERB222 guide, the Basalt Petrogenesis and Mantle Melting chapter explains week 2 · decompression melting · solidus and liquidus · binary phase diagrams · basalt tetrahedron · alkali basalt versus tholeiite · primary and primitive magmas.
- What does ERB222 cover on partial melting and trace element behaviour?
- In AskSia Library's ERB222 guide, the Partial Melting and Trace Element Behaviour chapter explains workshops 2 and 3 · residue mass balance · partition coefficients · bulk D · batch melting of melt and residue · primitive-mantle normalised patterns.
- What does ERB222 cover on granites, rhyolites and crustal melting?
- In AskSia Library's ERB222 guide, the Granites, Rhyolites and Crustal Melting chapter explains week 3 · evidence for crustal melting · fluid-absent melting of micas · haplogranite minimum · Buddington depth zones · I, S, A and M types · alumina saturation.
What ERB222 covers
Twelve chapters follow the weekly lectures, practicals and workshops from rock description to isotopes and ages.
Igneous Classification and Rock Description
Week 1 · coherent versus clastic · phenocrysts and groundmass · grain size and crystallinity · QAP modal naming · CIPW norm and silica saturationStart with texture and setting, not the name
The Week 1 lecture treats composition and texture as the two properties that carry most of the information in an igneous rock.
- Coherent versus clastic rocks
- Plutonic, subvolcanic and volcanic settings
- Phenocrysts and groundmass
- Grain size and crystallinity terms
- QAP modal classification
- CIPW norm and silica saturation
Basalt Petrogenesis and Mantle Melting
Week 2 · decompression melting · solidus and liquidus · binary phase diagrams · basalt tetrahedron · alkali basalt versus tholeiite · primary and primitive magmasHow a solid mantle makes basalt
The Week 2 lecture starts from a puzzle: the mantle is solid, yet basalt erupts in every tectonic setting. The answer is decompression melting.
- Decompression melting and the mantle solidus
- Partial melting of lherzolite
- Solid solution loops for plagioclase and olivine
- Eutectic, peritectic and incongruent melting
- Basalt tetrahedron and critical planes
- Alkali basalt versus MORB tholeiite
Partial Melting and Trace Element Behaviour
Workshops 2 and 3 · residue mass balance · partition coefficients · bulk D · batch melting of melt and residue · primitive-mantle normalised patternsTwo workshops, one Problem-Solving Task
Workshops 2 and 3 turn the Week 2 melting story into numbers, and Problem-Solving Task 1 asks for a one-page explanation of how partial melting of the mantle creates diverse magmas using those results.
- Partition coefficients and bulk D
- Batch melting of the melt
- Residual solid after batch melting
- Major element residue mass balance
- Lherzolite to harzburgite depletion
- Primitive mantle normalisation
Granites, Rhyolites and Crustal Melting
Week 3 · evidence for crustal melting · fluid-absent melting of micas · haplogranite minimum · Buddington depth zones · I, S, A and M types · alumina saturationGranite needs a crustal source
Melting mantle peridotite yields basalt, yet thick batholiths and huge rhyolite eruptions sit almost entirely on the continents.
- Evidence for crustal melting
- Heat from basalt underplating
- Fluid-absent melting of micas
- Haplogranite ternary minimum
- Granitoid textures and intrusion types
- Buddington depth zones
Magma Chamber Processes and Crystallisation
Week 4 · magma storage in the crust · crystallisation sequences · Bowen's series · solid solution and eutectic paths · differentiation trendsWhere rising magma stops
Most magma never reaches the surface.
- Magma ascent and stalling
- Storage depth and space making
- Solidification fronts and mush
- Crystal settling and flotation
- Binary eutectic crystallisation
- An-Di-Fo ternary paths
Fractional Crystallisation Modelling
Weeks 4 and 5 and Problem-Solving Task 2 · Harker variation diagrams · compatible and incompatible trends · AFM tholeiitic versus calc-alkaline pathsCrystals that leave change the liquid
Fractional crystallisation modifies a magma by growing crystals and then separating them from the melt, by settling or by compaction of a crystal mush that squeezes interstitial liquid out.
- Crystal removal by settling and mush compaction
- Liquid line of descent
- Harker variation diagrams
- Compatible and incompatible trends
- Inflections where a new phase joins
- Parental and derivative magmas
Magma Mixing, Assimilation and Layered Intrusions
Weeks 5 and 6 · cumulates and layered intrusions · magma mixing and mingling · assimilation · plagioclase-melt equilibrium · disequilibrium texturesLayered intrusions as fractionation records
The Week 5 lecture uses layered mafic intrusions, above all Skaergaard in Greenland, as the clearest natural record of crystal fractionation.
- Layered mafic intrusions and cumulates
- Rhythmic and cryptic layering
- Magma mingling and enclaves
- Magma mixing and linear arrays
- Assimilation-fractional crystallisation
- Autocrysts, antecrysts and xenocrysts
Volcanic Processes and Pyroclastic Rocks
Weeks 6 and 7 · eruption and emplacement · fall, surge and flow deposits · ignimbrite welding and fiamme · describing clastic volcanic rocksEruption style leaves the last word in the rock
Week 6 argues that conduit and eruption processes stamp strong textures on volcanic rocks, so much of what you see in a lava or tuff may record only the final stage of a magma's history.
- Effusive versus explosive eruptions
- Degassing and strombolian scoria
- Fall, surge and flow deposits
- Welding grade and eutaxitic fabric
- Basal vitrophyre and devitrified interiors
- Clastic description order
Mapping and Sampling Igneous Rocks
Weeks 7 and 8 · compass and strike and dip · field fact map versus geologic map · Noosa field project · report and map criteriaObservation comes first
Week 7 prepares you for the Noosa field trip by treating earth science as an observation-based discipline.
- Geological compass and magnetic declination
- Strike, dip and dip direction notation
- Converting strike to dip azimuth
- Lineation trend and plunge
- Field fact map versus geologic map
- Field report structure and criteria
The Subduction Factory and Calc-Alkaline Magmas
Week 9 · slab dehydration and flux melting · mantle wedge · andesite petrography · calc-alkaline versus tholeiitic series · arc magma evolutionThe third way to make magma
Week 9 completes the unit's account of magma generation. Oceanic crust altered on the seafloor is carried down a subduction zone, where hydrous minerals such as chlorite and amphibole break down with increasing pressure.
- Slab dehydration and flux melting
- Mantle wedge and the subduction factory
- Arc geometry and slab dip
- Island arcs versus continental arcs
- Tholeiitic versus calc-alkaline trends on the AFM diagram
- Effects of water and pressure on crystallisation
Radiogenic Isotopes as Magma Tracers
Weeks 10 and 11 · isotopes and decay · Rb-Sr and Sm-Nd systems · MORB and OIB reservoirs · epsilon Nd · mixing and crustal inputRatios that survive melting
Isotopes of one element share their chemistry, so partial melting and fractional crystallisation cannot separate them. A magma therefore carries the 87Sr/86Sr and 143Nd/144Nd of its source.
- Stable versus radioactive isotopes
- Why chemical fractionation leaves isotope ratios intact
- Depleted and enriched mantle reservoirs
- Epsilon Nd relative to CHUR
- Age correction to initial ratios
- Two-component mixing between mantle and crust
Geochronology and Igneous Timescales
Weeks 10 and 11 · decay law and half-life · isochron ages · U-Pb zircon dating · initial ratios · timescales of magma storageWhat a radiometric age actually measures
Radioactive isotopes decay to a different isotope at a constant rate, so the amount of parent left and daughter grown records elapsed time.
- Radioactive decay law and half-life
- Decay constants and useful age ranges
- Rb-Sr isochron slope and initial ratio
- U-Pb zircon ages from Pb/U
- Inherited and discordant zircons
- Blocking temperature
The unit homepage describes rocks as tracers of magma sources, conditions of melting, storage in the crust and eruption at the surface, and it works across every scale from outcrop to thin section, adding mineral, glass and whole-rock chemistry, radiogenic isotopes and geochronology.
The Week 1 lecture explains that the unit began in 2025 by combining the igneous petrology of ERB206 with the high-temperature geochemistry of ERB301, and that it assumes the mineral knowledge of ERB220.
How the semester runs
Lectures move from rock description and classification through basalt petrogenesis, granite and rhyolite genesis, two weeks of magma chamber processes, volcanism, mapping and sampling, the subduction factory, radiogenic isotopes and geochronology.
Practicals train systematic hand-specimen and thin-section description of basalts, granites, ignimbrites and andesites. Workshops turn the lecture ideas into calculations on real geochemical data, and three of them feed the Problem-Solving Tasks.
A three-day field trip to Noosa in Week 8 supplies the rocks, thin sections and whole-rock data for the Field Project.
Where the marks are
Half of the grade sits in Week 13: a two-hour theory exam and a two-hour practical exam, each worth 25%.
The practical exam gives you unknown samples to describe and interpret, so speed and consistency with the description routine matter as much as knowledge, which is why Task 1 asks you to develop one method and use it on every rock. The coordinator's exam tips stress precise terminology, the ability to read every lecture figure as evidence, and confident use of classification diagrams.
Worked example · free
Batch melting: how the degree of melting sets an incompatible element
- 1Write the batch melting equation: cl = co / [D + f(1 - D)], with co = 1.0 ppm and D = 0.01.
- 1At f = 0.05 the denominator is 0.01 + 0.05 x 0.99 = 0.0595, so cl = 1.0 / 0.0595 = 16.8 ppm.
- 1At f = 0.20 the denominator is 0.01 + 0.20 x 0.99 = 0.208, so cl = 1.0 / 0.208 = 4.81 ppm.
- 1The 5% melt is about 3.5 times richer, matching the lecture link between low degrees of melting and alkali basalt, and higher degrees and tholeiite.
Key terms
- Primary Magma
- A magma whose composition is unchanged from the moment it left its source until it solidified.
- Primitive Magma
- A mantle-derived basaltic magma that is close to unevolved, with MgO above about 6 wt% and few phenocrysts.
- Solidus
- The temperature boundary below which no liquid can exist in a rock.
- Liquidus
- The temperature boundary above which no solid phase remains.
- Eutectic
- The lowest temperature at which a liquid can exist in a system at a given pressure, where the first melt always forms.
- Bulk Partition Coefficient
- The sum of each mineral's partition coefficient multiplied by that mineral's proportion in the rock.
- Incompatible Element
- An element with a partition coefficient below one, so it prefers the melt over the crystals.
- Restite
- The refractory solid residue left behind after partial melting has removed the melt.
- Cumulate
- A rock formed by the accumulation of crystals that separated from a magma.
- Ignimbrite
- The poorly sorted, massive deposit of a pyroclastic density current, made of pumice, crystals and lithic fragments in an ash matrix.
- Calc-Alkaline Series
- A subalkaline magma series typical of subduction zones that lacks strong iron enrichment on the AFM diagram.
- Isochron
- A straight line on a parent-daughter isotope plot whose slope gives the age of a cogenetic suite of samples.
- Decay Constant
- The fraction of radioactive nuclides that decay per unit time, written as lambda in the decay equation.
ERB222 FAQ
How are the Week 13 exams split between theory and practical?
The examination item is worth 50% and is split evenly. A two-hour theory exam sits in the Week 13 lecture slot and a two-hour practical exam sits in the practical slot, each worth 25%. Task 1 lists four hours in total, an individual percentage mark, and an exam booklet handed in at the end of each paper.
What happens in the practical exam?
Task 1 says the practical exam includes a suite of unknown samples whose mineralogy and textures you describe before interpreting origin, composition and rock type. It singles out three calls to make with confidence: coherent versus clastic, plutonic versus volcanic, and what separates an intermediate rock from a more mafic or a more silicic one.
How do the Problem-Solving Tasks work?
They are individual workshop tasks worth 35% together, built on real geochemical data. Partial Melting draws on Workshops 2 and 3 for 10%, Fractional Crystallisation on Workshop 5 for 10%, and Isotopes on Workshops 10 and 11 for 15%. Not every workshop is assessed, and you are told which ones count, so attending and finishing each workshop matters.
What does the Field Project involve?
It follows the three-day Noosa field trip and is worth 15%. An individual field report worth 10% integrates field observations, thin sections and supplied whole-rock geochemistry, with no more than 10 pages before appendices. A group map worth 5% includes the field fact map, a complete geologic map of the Noosa Headland area and a key sample description.
Which parts of the unit do students find hardest?
The Week 1 lecture says weak mineral identification was a clear factor in students failing in 2025. The exam tips add that terminology causes confusion, for example tholeiite versus alkaline versus calc-alkaline, and that the first two weeks and the last lectures are remembered and understood worst. Revise those early chapters first rather than leaving them until the end.
Are past exam papers available for revision?
No past theory or practical exam paper appears among the unit materials available here. The coordinator points students to the Canvas Preparation Quiz for practice examples of classification diagrams, and to the representative samples and thin sections that can be examined in and out of class. The practice questions in this guide are newly written to match the published question styles.
How much calculation should I expect?
Workshop calculations underpin all three Problem-Solving Tasks: batch melting with bulk partition coefficients, residue mass balance, plagioclase and melt equilibrium, isochron ages from rubidium and strontium, uranium and lead ages, and epsilon neodymium. The theory exam also asks you to read classification and phase diagrams, so practise plotting modal data as well as computing ratios.
Questions students ask in each ERB222 chapter
- What should come first when describing an unknown igneous sample?
- Decide whether the rock is coherent or clastic, because that choice changes the whole description template. Coherent rocks need phenocrysts, groundmass and crystallinity; clastic rocks need clast types, sorting, matrix and fabric before any mineral list. Chapter 01 · Igneous Classification and Rock Description
- Why does the mantle melt at mid-ocean ridges if nothing heats it?
- Plates pulling apart let deep peridotite rise. The parcel loses almost no heat on the way up, but the pressure drop lowers its melting temperature, so the rock crosses its solidus. Raising temperature, as in plumes, and adding water, as in subduction zones, are the other two routes the unit covers. Chapter 02 · Basalt Petrogenesis and Mantle Melting
- How do I calculate bulk D for a mantle rock?
- Multiply each mineral's partition coefficient by that mineral's fraction of the rock and add the products. The workshop lherzolite uses 60% olivine, 30% orthopyroxene and 10% clinopyroxene and ignores the 1 to 3% aluminous phase. A mineral with a high Kd can dominate D even when it is scarce. Chapter 03 · Partial Melting and Trace Element Behaviour
- Why can't decompression melting make granite?
- Continental crust is solid in its normal state, and lowering the pressure on it does not produce melt, so some thermal disturbance is required. That heat comes mostly from basaltic magma trapped at the Moho or intruded into the lower crust, which lifts the geotherm until hydrous minerals start to break down. Chapter 04 · Granites, Rhyolites and Crustal Melting
- How deep are magma chambers under volcanoes?
- Seismic and petrological studies beneath Mount St Helens and Long Valley place crustal storage zones at about 5 to 15 km. Storage concentrates at traps such as the Moho and the brittle to ductile transition, yet pressures recorded by pyroxene and amphibole show crystallisation can happen at many levels. Chapter 05 · Magma Chamber Processes and Crystallisation
- How do you tell a tholeiitic suite from a calc-alkaline suite on an AFM diagram?
- Plot every sample from the suite rather than one rock. If the array climbs toward the iron apex, bending concave downward above the dividing line before swinging toward the alkali corner, it is tholeiitic. If it runs from the magnesium side toward alkalis and stays mostly below the line, it is calc-alkaline. Chapter 06 · Fractional Crystallisation Modelling
- What is the difference between magma mingling and magma mixing?
- Mingling keeps the two magmas physically distinct, so you see enclaves with chilled, cuspate margins or streaky pumice but no intermediate chemistry. Mixing produces a hybrid, and its analyses fall on a straight line between the two end members. Enclaves prove at least mingling; hybrids are needed to claim mixing. Chapter 07 · Magma Mixing, Assimilation and Layered Intrusions
- How can you tell a fall deposit from an ignimbrite in the field?
- Look at sorting and layering first. Fall deposits are the best sorted pyroclastic deposits, clast-supported where lapilli-grade, and they drape topography as planar mantle bedding. Ignimbrites, laid down from high-concentration pyroclastic flows, are massive and very poorly sorted. Cross-bedding from a turbulent, dilute current instead points to a surge deposit. Chapter 08 · Volcanic Processes and Pyroclastic Rocks
- What is the difference between a field fact map and a geologic map?
- The fact map is made in the field and records only what was observed: numbered stops, outcrop areas, strike and dip readings, traced contacts, structures and rock types. The geologic map is the interpretation built on it, with the whole area filled by units, boundaries drawn solid or dashed by certainty, and a legend in relative stratigraphic order. Chapter 09 · Mapping and Sampling Igneous Rocks
- Why do arc volcanoes form at a fixed depth above the subducting plate?
- The controlling dehydration reactions depend on pressure. Hydrous minerals such as chlorite give up their water near 100 km, and that water triggers melting in the overlying wedge. A steeper slab reaches this depth closer to the trench, while a slab flatter than about 20 degrees can shut volcanism off. Chapter 10 · The Subduction Factory and Calc-Alkaline Magmas
- Why don't partial melting and crystallisation change Sr and Nd isotope ratios?
- Those processes separate elements by their chemical behaviour, and isotopes of one element behave almost identically. Only mass fractionation, a tiny effect, and radioactive decay alter the ratios, so a fresh magma records the 87Sr/86Sr and 143Nd/144Nd of its source. Chapter 11 · Radiogenic Isotopes as Magma Tracers
- Why is zircon used so often for U-Pb dating of granites?
- Zircon is a common accessory mineral in intermediate to felsic rocks, hard and resistant to weathering. It accepts uranium into its structure but excludes lead, so lead measured in a fresh grain is treated as radiogenic. Microprobe analysis at 10 to 30 micrometre spots also lets you date single grains and their cores separately. Chapter 12 · Geochronology and Igneous Timescales
How to study for the exam
Work in two tracks that mirror the two Week 13 papers. For the practical exam, run the description routine on every specimen and thin section you can access: decide coherent or clastic, place the rock as plutonic, subvolcanic or volcanic, list phenocrysts and groundmass separately, estimate abundances, then name the rock with the IUGS scheme and a descriptive name in template order.
Compare each unknown with the four representative samples from class, the basalt, granite, ignimbrite and andesite, and say which it most resembles and why. For the theory exam, take every figure in the lecture handouts and write two sentences for it: what the axes or apices are, and which process moves a sample across it.
Rebuild the workshop calculations by hand, especially batch melting, fractional crystallisation trends, isochron ages and epsilon neodymium, and check each answer against a limiting case. Start revision with Weeks 1, 2, 10 and 11, the material the coordinator says is remembered worst, and finish with a timed long-answer question in which each part feeds the next.
Your AI Science tutor for ERB222
Stuck on a hard ERB222 question? Sia is AskSia’s AI Science tutor — ask any ERB222 Igneous Petrology and Geochemistry question and get a clear, step-by-step explanation grounded in how the course is actually taught and assessed. Read this whole study guide free, then take your hardest questions to Sia.
