Maghemite

Key takeaways

Maghemite belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Maghemite to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Maghemite from memory before moving on to harder problems.

Reference excerpt

Maghemite (Fe2O3, γ-Fe2O3) is a member of the family of iron oxides. It has the same formula as hematite, but the same spinel ferrite structure as magnetite (Fe3O4) and is also ferrimagnetic. It is sometimes spelled as "maghaemite". Maghemite can be considered as an Fe(II)-deficient magnetite with formula

( Fe 8 III ) A [ Fe 40 3 III ◻ 8 3 ] B O 32 {\displaystyle \left({\ce {Fe^{III}8}}\right)_{A}\left[{\ce {Fe_{40/3}^{III}\square _{8/3}}}\right]_{B}{\ce {O32}}}

where

◻ {\displaystyle \square } represents a vacancy, A indicates tetrahedral and B octahedral positioning.

Occurrence Maghemite forms by weathering or low-temperature oxidation of spinels containing iron(II) such as magnetite or titanomagnetite. Maghemite can also form through dehydration and transformation of certain iron oxyhydroxide minerals, such as lepidocrocite and ferrihydrite. It occurs as widespread brown or yellow pigment in terrestrial sediments and soils. It is associated with magnetite, ilmenite, anatase, pyrite, marcasite, lepidocrocite and goethite. It is known to also form in areas that have been subjected to bushfires (particularly in the Leonora area of Western Australia) magnetising iron minerals. Maghemite was named in 1927 for an occurrence at the Iron Mountain Mine, northwest of Redding, Shasta County, California. The name alludes to somewhat intermediate character between magnetite and hematite. It can appear blue with a grey shade, white, or brown. It has isometric crystals. Maghemite is formed by the topotactic oxidation of magnetite.

Cation distribution There is experimental and theoretical evidence that Fe(III) cations and vacancies tend to be ordered in the octahedral sites, in a way that maximizes the homogeneity of the distribution and therefore minimizes the electrostatic energy of the crystal.

Electronic structure Maghemite is a semiconductor with a bandgap of ca. 2 eV, although the precise value of the gap depends on the electron spin.

Applications Maghemite exhibits ferrimagnetic ordering with a high Néel temperature (~950 K), which together with its low cost and chemical stability led to its wide application as a magnetic pigment in electronic recording media since the 1940s. Maghemite nanoparticles are used in biomedicine, because they are biocompatible and non-toxic to humans, while their magnetism allows remote manipulation with external fields.

As pollutant It was found in 2022 that high levels of maghemite particles small enough to enter the bloodstream if inhaled, some as small as five nanometres, were present in the London Underground transport system. The presence of the particles indicated that they are suspended for long periods due to poor ventilation, particularly on platforms. The health implications presented by the particles were not investigated.

References

Illustrations

Worked examples

Example 1 — a first encounter with Maghemite

Start with the simplest possible case. Write down what Maghemite claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Maghemite before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Maghemite ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Maghemite

In research: Maghemite appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Maghemite in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Maghemite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cubic minerals, Ilmenite group, Iron(III) minerals, so understanding it makes those chapters shorter.
In everyday life: Look for Maghemite outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Maghemite in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Maghemite means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Maghemite out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Maghemite in simple terms?

Maghemite (Fe2O3, γ-Fe2O3) is a member of the family of iron oxides. It has the same formula as hematite, but the same spinel ferrite structure as magnetite (Fe3O4) and is also ferrimagnetic.

Why does Maghemite matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Maghemite?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Maghemite.