science

Restite

Restite 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 Restite rather than just read about it. In short: Restite is the residual material left at the site of melting during the in place production of magma. Generally, restite is composed of a predominance of mafic minerals because these are harder to melt (see Bowen's reaction series).

Key takeaways

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

Reference excerpt

Restite is the residual material left at the site of melting during the in place production of magma. Generally, restite is composed of a predominance of mafic minerals because these are harder to melt (see Bowen's reaction series). Typical minerals are amphibole, biotite, pyroxene, ilmenite or other iron oxides and some plagioclase feldspar. When chunks of restite are caught up within the granite it is known as a restite inclusion or enclave.

S-type restite reactions Restite in S-type granites is produced from the melting, within the Earth's crust, of a typical metamorphic mineral assemblage of high-pressure gneiss of sedimentary origin;

biotite + quartz + feldspars → hydroxyl-bearing melt + orthopyroxene + cordierite + residual feldspars The melt reaction produces a granitic melt and solid orthopyroxene and cordierite. Cordierite in restite inclusions is unstable at low pressures; this reverts to Al-rich mica and quartz during ascent with the entraining magma. Orthopyroxene, unstable at low temperatures, reverts to an assemblage of biotite plus quartz. Restite feldspars will typically be a sodic plagioclase. Thus, restite inclusions in S-type granites will be a recrystallised granoblastic textured inclusion of biotite-muscovite-feldspar-quartz. If the restite minerals are carried with the magma, as the minerals become thermo-barometrically unstable during ascent, they will react back with the magma to form biotite from orthopyroxene, and feldspar or mica from cordierite. These reactions also involve consumption of significant quantities of water, and hence, will preclude the generation of a hydrothermal solution.

I-type restite reactions Restite reactions in I-type granites are essentially similar, but due to the mafic and granitic source rocks, the restite assemblage is predisposed to produce an orthopyroxene + clinopyroxene + plagioclase +/- garnet assemblage. Similar to the reactions occurring in S-type granites, the restite minerals will revert to hornblende and plagioclase upon ascent, resorbing water and precluding generation of hydrothermal solutions. Porphyry copper deposits are generally associated with I-type granites which are not restite mediated.

Importance of restite Restite is an important constituent in fractional crystallisation and igneous differentiation processes. Restite acts as a form of buffer within magma, acting as a reservoir primarily of water and water-adsorbent minerals, which may prevent or retard a granitic magma from attaining water saturation. This is analogous to the behaviour of a chemical buffer solution or mineral redox buffer except in this case it is a mineral-water exchange. This process occurs by hydration of ferromagnesian minerals, particularly hornblende, which may adsorb up to 5% H2O, and by conversion of pyroxene to hornblende during melting or fractionation at temperatures below the pyroxene stability field. This process is envisaged as, for instance, pyroxene-bearing restite inclusions 'soaking up' water and being converted to hydrous hornblende-bearing inclusions. Secondly, restite acts as a compositional buffer, providing elements to the surrounding magma as it is melted and ground up by erosive forces within the ascending magma. Restite can, in large enough amounts, retard the compositional changes of a magma either via providing more reagents or physically trapping crystals within the magma. Generally, restite is not present within magmas in large amounts and thus the effects of the above processes are not usually profound. However, it is likely that, particularly for S-type granite which is formed by wholesale anatexis (melting) of metasedimentary rocks, restite mediated melting and fractionation is crucial to the composition and behaviour of these magmas. In magmas which do not have a restite component, such as most M-type granites, some A-type granites, and most basaltic magmas, it is much easier for these magmas to achieve more dramatic fractional crystallization effects.

Worked examples

Example 1 — a first encounter with Restite

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

In research: Restite 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 Restite 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: Restite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Igneous rocks, Metamorphic rocks, Petrology, so understanding it makes those chapters shorter.
In everyday life: Look for Restite 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 Restite in 20 minutes

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

Frequently asked questions

What is Restite in simple terms?

Why does Restite 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 Restite?

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 Restite.