Spinel

Key takeaways

Spinel 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 Spinel to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Spinel from memory before moving on to harder problems.

Reference excerpt

Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula MgAl2O4 in the cubic crystal system. The name comes from the Latin word spinella, a diminutive form of spine, in reference to its pointed crystals.

Properties Spinel crystallizes in the isometric system; common crystal forms are octahedra, usually twinned. It has no true cleavage, but shows an octahedral parting and a conchoidal fracture. Its hardness is 8, its specific gravity is 3.5–4.1, and it is transparent to opaque with a vitreous to dull luster. It may be colorless, but usually comes in shades of red, lavender, blue, green, brown, black, or yellow. Chromium(III) causes the red color in spinel from Myanmar.

History Some spinels are among the most famous gemstones; these include the Black Prince's Ruby and the Timur Ruby in the British Crown Jewels, and the "Côte de Bretagne", formerly from the French Crown jewels. The Samarian Spinel, the largest known spinel in the world, weighs 500 carats (100 g).

Nomenclature The transparent red spinels were called spinel-rubies or balas rubies. Before the development of modern science and the establishment of a formal definition of "ruby", the name was also applied to spinels. "Balas" derives from Balascia, the ancient name for Badakhshan, a region in central Asia situated in the upper valley of the Panj River, one of the principal tributaries of the Oxus River. However, "Balascia" itself may be derived from Sanskrit bālasūryaka, which translates as "crimson-coloured morning sun". Mines in the Gorno Badakhshan region of present-day Tajikistan constituted for centuries the main source for red and pink spinels.

Occurrence

Geologic occurrence Spinel is found as a metamorphic mineral in metamorphosed limestones and silica-poor mudstones. It also occurs as a primary mineral in rare mafic igneous rocks; in these igneous rocks, the magmas are relatively deficient in alkalis relative to aluminium, and aluminium oxide may form as the mineral corundum or may combine with magnesia to form spinel. This is why spinel and ruby are often found together. The spinel petrogenesis in mafic magmatic rocks is strongly debated, but certainly results from mafic magma interaction with more evolved magma or rock (e.g. gabbro, troctolite). Spinel, (Mg,Fe)(Al,Cr)2O4, is common in peridotite in the uppermost Earth's mantle, between approximately 20 km to approximately 120 km, possibly to lower depths depending on the chromium content. At significantly shallower depths, above the Moho, calcic plagioclase is the more stable aluminous mineral in peridotite while garnet is the stable phase deeper in the mantle below the spinel stability region. Spinel, (Mg,Fe)Al2O4, is a common mineral in the Ca-Al-rich inclusions (CAIs) in some chondritic meteorites.

Geographical occurrence Spinel has long been found in the gemstone-bearing gravel of Sri Lanka and in limestones of the Badakshan Province in modern-day Afghanistan and Tajikistan; and of Mogok in Myanmar. Over the last decades gem quality spinels are found in the marbles of Lục Yên District (Vietnam), Mahenge and Matombo (Tanzania), Tsavo (Kenya) and in the gravels of Tunduru (Tanzania) and Ilakaka (Madagascar). Since 2000, in several locations around the world, spinels have been discovered with unusual vivid pink or blue colors. Such "glowing" spinels are known from Mogok (Myanmar), Mahenge plateau (Tanzania), Lục Yên District (Vietnam) and some more localities. In 2018 bright blue spinels have been reported also in the southern part of Baffin Island (Canada). The pure blue coloration of spinel is caused by small additions of cobalt.

Synthetic spinel

Synthetic spinel can be produced by similar means to synthetic corundum, including the Verneuil method and the flux method pioneered by Edmond Frémy. It is widely used as an inexpensive cut gem in birthstone jewelry for the month of August. Light blue synthetic spinel is a good imitation of aquamarine beryl, and green synthetic spinel is used as an emerald or tourmaline simulant. By 2015, transparent spinel was being made in sheets and other shapes through sintering. Synthetic spinel, which looks like glass but has notably higher strength against pressure, can also have applications in military and commercial use. Spinel-type chalcogenides are also investigated as optoelectronic semiconductors. In 2025, Hanzawa et al. reported d0-cation spinel sulfides based on ZnSc2S4 and (Zn,Mg)Sc2S4 with color-tunable direct band gaps and ambipolar dopability.

See also Minerals portal Aluminium oxynitride Ceylonite The Three Brothers, a lost 14th-century crown jewel with three red spinels in a triangular arrangement

References

Bibliography Deer, Howie and Zussman (1966). An Introduction to the Rock-Forming Minerals, Longman, pp. 424–433, ISBN 0-582-44210-9. Shumann, Walter (2006). Gemstones of the World 3rd edition, Sterling, pp. 116–117.

External links

Spinel structure at the University of Wisconsin - Green Bay Spinel structure at the Institut for materials science of the University of Kiel Value of Spinel

Illustrations

Worked examples

Example 1 — a first encounter with Spinel

Start with the simplest possible case. Write down what Spinel 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 Spinel 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 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

In research: Spinel 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 Spinel 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 is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aluminium minerals, Cubic minerals, Luminescent minerals, so understanding it makes those chapters shorter.
In everyday life: Look for Spinel 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 Spinel in 20 minutes

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

Frequently asked questions

What is Spinel in simple terms?

Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula MgAl2O4 in the cubic crystal system.

Why does Spinel 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 Spinel?

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.