science

Spinel group

Spinel group is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Spinel group rather than just read about it. In short: In minerology, the spinels are any of a class of minerals of general formulation AB2X4 which crystallise in the cubic (isometric) crystal system, with the X anions (typically chalcogens, like oxygen and sulfur) arranged in a close-packed cubic lattice and the cations A and B occupying some or all of the octahedral and tetrahedral sites in the lattice. Although the charges of A and B in the prototypical spinel struct…

Key takeaways

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

Reference excerpt

In minerology, the spinels are any of a class of minerals of general formulation AB2X4 which crystallise in the cubic (isometric) crystal system, with the X anions (typically chalcogens, like oxygen and sulfur) arranged in a close-packed cubic lattice and the cations A and B occupying some or all of the octahedral and tetrahedral sites in the lattice. Although the charges of A and B in the prototypical spinel structure are +2 and +3, respectively (A2+B3+2X2−4), other combinations incorporating divalent, trivalent, or tetravalent cations, including magnesium, zinc, iron, manganese, aluminium, chromium, titanium, and silicon, are also possible. The anion is normally oxygen; when other chalcogenides constitute the anion sublattice the structure is referred to as a thiospinel. A and B can also be the same metal with different valences, as is the case with magnetite, Fe3O4 (as Fe2+Fe3+2O2−4), which is the most abundant member of the spinel group. It is even possible for them to be alloys, as seen for example in LiNi0.5Mn1.5O4, a material used in some high energy density lithium ion batteries. Spinels are grouped in series by the B cation. The group is named for spinel (MgAl2O4), which was once known as "spinel ruby". (Today the term ruby is used only for corundum.)

Spinel group members Members of the spinel group include:

Aluminium spinels: Spinel: MgAl2O4, after which this class of minerals is named Gahnite: ZnAl2O4 Hercynite: FeAl2O4 Galaxite: MnAl2O4 Pleonaste: (Mg,Fe)Al2O4 Iron spinels: Cuprospinel: CuFe2O4 Franklinite: (Fe,Mn,Zn)(Fe,Mn)2O4 Jacobsite: MnFe2O4 Magnesioferrite: MgFe2O4 Magnetite: FeFe2O4, where one Fe is +2 and two Fe's are +3, respectively. Trevorite: NiFe2O4 Ulvöspinel: TiFe2O4 Zinc ferrite: (Zn,Fe)Fe2O4 Chromium spinels: Chromite: FeCr2O4 Magnesiochromite: MgCr2O4 Zincochromite: ZnCr2O4 Cobalt spinels: Manganesecobaltite: Mn1.5Co1.5O4 Vanadium spinels: Coulsonite: FeV2O4 Magnesiocoulsonite: MgV2O4 Others with the spinel structure: Ringwoodite: (Mg,Fe)2SiO4, an abundant olivine polymorph within the Earth's mantle from about 520 to 660 km depth, and a rare mineral in meteorites Musgravite: Be(Mg,Fe,Zn)2Al6O12 a type of "multi-spinel". There are many more compounds with a spinel structure, e.g. the thiospinels and selenospinels, that can be synthesized in the lab or in some cases occur as minerals. The heterogeneity of spinel group members varies based on composition with ferrous and magnesium based members varying greatly as in solid solution, which requires similarly sized cations. However, ferric and aluminium based spinels are almost entirely homogeneous due to their large size difference.

The spinel structure

The space group for a spinel group mineral may be Fd3m (the same as for diamond), but in some cases (such as spinel itself, MgAl2O4, beyond 452.6 K) it is actually the tetrahedral F43m.

Normal spinel structures have oxygen ions closely approximating a cubic close-packed latice with eight tetrahedral and four octahedral sites per formula unit (but eight times as many per unit cell). The tetrahedral spaces are smaller than the octahedral spaces. B ions occupy half the octahedral holes, while A ions occupy one-eighth of the tetrahedral holes. The mineral spinel MgAl2O4 has a normal spinel structure. In a normal spinel structure, the ions are in the following positions, where i, j, and k are arbitrary integers and δ, ε, and ζ are small real numbers (note that the unit cell can be chosen differently, giving different coordinates):

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Spinel group

Start with the simplest possible case. Write down what Spinel group claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In 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 Spinel group 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 Spinel group 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 Spinel group

In research: Spinel group appears in 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 Spinel group 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: Spinel group is common in secondary-school and first-year university syllabi. It links to neighbouring topics Spinel group, so understanding it makes those chapters shorter.
In everyday life: Look for Spinel group 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Spinel group” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Spinel group in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Spinel group 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 Spinel group out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Spinel group in simple terms?

Why does Spinel group matter?

Because it connects several 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 Spinel group?

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 Spinel group.