earth science

Stishovite

Stishovite is a earth 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 Stishovite rather than just read about it. In short: Stishovite ( STISH-ə-vyte) is an extremely hard, dense tetragonal form (polymorph) of silicon dioxide. It is very rare on the Earth's surface; however, it may be a predominant form of silicon dioxide in the Earth, especially in the lower mantle.

Key takeaways

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

Reference excerpt

Stishovite ( STISH-ə-vyte) is an extremely hard, dense tetragonal form (polymorph) of silicon dioxide. It is very rare on the Earth's surface; however, it may be a predominant form of silicon dioxide in the Earth, especially in the lower mantle. Stishovite was named after Sergey Stishov, a Soviet high-pressure physicist who first synthesized the mineral in 1961. It was then discovered in Meteor Crater in 1962 by Edward C. T. Chao. Unlike other silica polymorphs, the crystal structure of stishovite resembles that of rutile (TiO2). The silicon in stishovite adopts an octahedral coordination geometry, being bound to six oxides. Similarly, the oxides are three-connected, unlike low-pressure forms of SiO2. In most silicates, silicon is tetrahedral, being bound to four oxides. It was long considered the hardest known oxide (~30 GPa Vickers); however, boron suboxide has been discovered in 2002 to be much harder. At normal temperature and pressure, stishovite is metastable. Stishovite can be separated from quartz by applying hydrogen fluoride (HF); unlike quartz, stishovite will not react.

Appearance Large natural crystals of stishovite are extremely rare and are usually found as clasts of 1 to 2 mm in length. When found, they can be difficult to distinguish from regular quartz without laboratory analysis. It has a vitreous luster, is transparent (or translucent), and is extremely hard. Stishovite usually sits as small rounded gravels in a matrix of other minerals.

Synthesis Until recently, the only known occurrences of stishovite in nature formed at the very high shock pressures (>100 kbar, or 10 GPa) and temperatures (> 1200 °C) present during hypervelocity meteorite impact into quartz-bearing rock. Minute amounts of stishovite have been found within diamonds, and post-stishovite phases were identified within ultra-high-pressure mantle rocks. Stishovite may also be synthesized by duplicating these conditions in the laboratory, either isostatically or through shock (see shocked quartz). At 4.287 g/cm3, it is the second densest polymorph of silica, after seifertite. It has tetragonal crystal symmetry, P42/mnm, No. 136, Pearson symbol tP6.

See also Coesite, another mineral form of silicon dioxide Thaumasite, another rare mineral with hexacoordinated octahedral silica

References

External links Properties of stishovite Stishovite's origin in meteor impacts

Illustrations

Worked examples

Example 1 — a first encounter with Stishovite

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

In research: Stishovite 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 Stishovite 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: Stishovite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Impact event minerals, Minerals in space group 136, Silica polymorphs, so understanding it makes those chapters shorter.
In everyday life: Look for Stishovite 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.

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How to study Stishovite in 20 minutes

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

Frequently asked questions

What is Stishovite in simple terms?

Why does Stishovite 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 Stishovite?

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 Stishovite.