science

Talc carbonate

Talc carbonate 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 Talc carbonate rather than just read about it. In short: Talc carbonates are a suite of rock and mineral compositions found in metamorphosed ultramafic rocks. The term refers to the two most common end-member minerals found within ultramafic rocks which have undergone talc-carbonation or carbonation reactions: talc and the carbonate mineral magnesite.

Key takeaways

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

Reference excerpt

Talc carbonates are a suite of rock and mineral compositions found in metamorphosed ultramafic rocks. The term refers to the two most common end-member minerals found within ultramafic rocks which have undergone talc-carbonation or carbonation reactions: talc and the carbonate mineral magnesite. Talc carbonate mineral assemblages are controlled by temperature and pressure of metamorphism and the partial pressure of carbon dioxide within metamorphic fluids, as well as by the composition of the host rock.

Compositional controls In a general sense, talc carbonate metamorphic assemblages are diagnostic of the magnesium content of the ultramafic protolith.

Lower-magnesian ultramafic rocks (12-18% MgO as a rule of thumb) tend to favor talc-chlorite assemblages Medium-MgO rocks (15-25% MgO) tend to produce talc-amphibole assemblages. High-MgO rocks with in excess of 25% MgO tend to form true talc-magnesite metamorphic assemblages. Thus, the MgO content of a metamorphosed ultramafic rock can be estimated by understanding the mineral assemblage of the rock. Magnesium content determines the proportion of talc and/or magnesite and aluminium-calcium-sodium content determines the proportion of amphibole and/or chlorite.

Talc carbonate minerals Several minerals are diagnostic of talc carbonated ultramafic rocks;

Talc Chlorite, generally magnesian bluish-green Tremolite-cummingtonite-grunerite amphiboles in greenschist facies rocks Anthophyllite-cummingtonite amphibole in weakly carbonated serpentinite at greenschist facies or very rarely, uncarbonated amphibolite facies serpentinites Magnesite, and rarely dolomite in association with amphibolitic compositions At amphibolite facies, the diopside-in isograd is reached (dependent on carbon dioxide partial pressure) and metamorphic assemblages trend toward talc-pyroxene and eventually toward metamorphic olivine.

Mineral reactions Serpentinisation of olivine:

forsterite2Mg2SiO4 + 3H2O → serpentineMg3Si2O5(OH)4 + bruciteMg(OH)2 Or by addition of aqueous silica:

3Mg2SiO4 + 4H2O + SiO2,aq → 2Mg3Si2O5(OH)4 Carbonation of serpentine to form talc-magnesite

2Mg3Si2O5(OH)4 + 3CO2 → Mg3Si4O10(OH)2 + 3MgCO3 + 3H2O

Occurrence Because carbon dioxide is such a common component of metamorphic fluids, talc-carbonated ultramafics are relatively common. However, the degree of talc-carbonation is usually somewhere between the two end-member compositions of pure serpentinite and pure talc-carbonate. It is common to see serpentinites which contain talc, amphibole and chloritic minerals in small proportions which infer the presence of carbon dioxide in the metamorphic fluid. Talc carbonate is present in many of the ultramafic bodies of the Archaean Yilgarn craton, Western Australia. Notably, the Widgiemooltha Komatiite shows pure talc-carbonation on the eastern flank of the Widgeimooltha Dome, and almost pure serpentinite metamorphism on the western flank.

Carbonation of other rocks Carbon dioxide has less severe impacts on mafic, felsic and rocks of other composition, such as carbonate rocks, chemical sediments, etcetera. The exception to this rule is the calc-silicate family of metamorphic rocks, which are also subjected to wide variations in mineral speciation due to the mobility of carbonate during metamorphism. Felsic and mafic rocks tend to be less affected by carbon dioxide due to their higher aluminium content. Ultramafic rocks lack aluminium, which allows carbonate to react with magnesium silicates to form talc. In rocks with extremely low aluminium contents, this reaction can progress to create magnesite. Advanced carbonation of felsic and mafic rocks, very rarely, creates fenite, a metasomatic alteration caused particularly by carbonatite intrusions. Fenite alteration is known, but very restricted in distribution, around high-temperature metamorphic talc-carbonates, generally in the form of a sort of aureole around ultramafics. Such examples include biotite-rich zones, amphibolite-calcite-scapolite alteration and other unusual skarn assemblages.

See also Amphibolite Granulite Greenschist Komatiite List of rock types Metamorphic rock Serpentinite Soapstone Ultramafic rocks

References

Worked examples

Example 1 — a first encounter with Talc carbonate

Start with the simplest possible case. Write down what Talc carbonate 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 Talc carbonate 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 Talc carbonate 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 Talc carbonate

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

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

Frequently asked questions

What is Talc carbonate in simple terms?

Why does Talc carbonate 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 Talc carbonate?

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 Talc carbonate.