earth science

Magnesite

Magnesite 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 Magnesite rather than just read about it. In short: Magnesite is a mineral with the chemical formula MgCO3 (magnesium carbonate). Iron, manganese, cobalt, and nickel may occur as admixtures, but only in small amounts.

Key takeaways

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

Reference excerpt

Magnesite is a mineral with the chemical formula MgCO3 (magnesium carbonate). Iron, manganese, cobalt, and nickel may occur as admixtures, but only in small amounts. Magnesite occurs naturally in both cryptocrystalline and crystalline forms depending on the conditions of formation. Magnesite is used in the production of magnesium oxide for the refractory lining of kilns and furnaces, as well as artistically in jewelry and sculpture. Since it may be formed by carbonation of magnesium serpentine, there have also been efforts to use magnesite for carbon sequestration.

Occurrence Magnesite occurs as veins in and an alteration product of ultramafic rocks, serpentinite and other magnesium rich rock types in both contact and regional metamorphic terrains. These magnesites are often cryptocrystalline and contain silica in the form of opal or chert.

Magnesite is also present within the regolith above ultramafic rocks as a secondary carbonate within soil and subsoil, where it is deposited as a consequence of dissolution of magnesium-bearing minerals by carbon dioxide in groundwaters. Crystalline and cryptocrystalline magnesites have very different mineral structures. While crystalline magnesite has a well developed crystal structure, the cryptocrystalline magnesite is amorphous- mostly aggregate of fine grains.

Formation Magnesite can be formed via talc carbonate metasomatism of peridotite and other ultramafic rocks. Magnesite is formed via carbonation of olivine in the presence of water and carbon dioxide at elevated temperatures and high pressures typical of the greenschist facies. Magnesite can also be formed via the carbonation of magnesium serpentine (lizardite) via the following reaction:

2 Mg3Si2O5(OH)4 + 3 CO2 → Mg3Si4O10(OH)2 + 3 MgCO3 + 3 H2O However, when performing this reaction in the laboratory, the trihydrated form of magnesium carbonate (nesquehonite) will form at room temperature. This very observation led to the postulation of a "dehydration barrier" being involved in the low-temperature formation of anhydrous magnesium carbonate. Laboratory experiments with formamide, a liquid resembling water, have shown how no such dehydration barrier can be involved. The fundamental difficulty to nucleate anhydrous magnesium carbonate remains when using this non-aqueous solution. Not cation dehydration, but rather the spatial configuration of carbonate anions creates the barrier in the low-temperature nucleation of magnesite. Magnesite has been found in modern sediments, caves and soils. Its low-temperature (around 40 °C [104 °F]) formation is known to require alternations between precipitation and dissolution intervals. The low-temperature formation of magnesite might well be of significance toward large-scale carbon sequestration. A major step forward toward the industrial production of magnesite at atmospheric pressure and a temperature of 316 K was described by Vandeginste. In those experiments small additions of hydrochloric acid alternated periodically with additions of sodium carbonate solution. Also new in these experiments was the very short duration of only a few hours for the alternating dissolution and precipitation cycles. Magnesite was detected in meteorite ALH84001 and on planet Mars itself. Magnesite was identified on Mars using infrared spectroscopy from satellite orbit. Near Jezero Crater, Mg-carbonates have been detected and reported to have formed in lacustrine environment prevailing there. Controversy still exists over the temperature of formation of these carbonates. Low-temperature formation has been suggested for the magnesite from the Mars-derived ALH84001 meteorite. Magnesium-rich olivine (forsterite) favors production of magnesite from peridotite. Iron-rich olivine (fayalite) favors production of magnetite-magnesite-silica compositions. Magnesite can also be formed by way of metasomatism in skarn deposits, in dolomitic limestones, associated with wollastonite, periclase, and talc. Resistant to high temperature and able to withstand high pressure, magnesite has been proposed to be one of the major carbonate bearing phase in Earth's mantle and possible carriers for deep carbon reservoirs. For similar reason, it is found in metamorphosed peridotite rocks in Central Alps, Switzerland and high pressure eclogitic rocks from Tianshan, China. Magnesite can also precipitate in lakes in presence of bacteria either as hydrous Mg-carbonates or magnesite.

Isotopic evidence

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Magnesite

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

In research: Magnesite 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 Magnesite 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: Magnesite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Calcite group, Carbonate minerals, Evaporite, so understanding it makes those chapters shorter.
In everyday life: Look for Magnesite 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 Magnesite in 20 minutes

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

Frequently asked questions

What is Magnesite in simple terms?

Magnesite is a mineral with the chemical formula MgCO3 (magnesium carbonate). Iron, manganese, cobalt, and nickel may occur as admixtures, but only in small amounts.

Why does Magnesite 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 Magnesite?

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 Magnesite.