earth science

Thaumasite

Thaumasite 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 Thaumasite rather than just read about it. In short: Thaumasite is a calcium silicate mineral, containing Si atoms in unusual octahedral configuration, with chemical formula Ca3Si(OH)6(CO3)(SO4)·12H2O, also sometimes more simply written as CaSiO3·CaCO3·CaSO4·15H2O. It occurs as colorless to white prismatic hexagonal crystals, typically as acicular radiating groups.

Key takeaways

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

Reference excerpt

Thaumasite is a calcium silicate mineral, containing Si atoms in unusual octahedral configuration, with chemical formula Ca3Si(OH)6(CO3)(SO4)·12H2O, also sometimes more simply written as CaSiO3·CaCO3·CaSO4·15H2O. It occurs as colorless to white prismatic hexagonal crystals, typically as acicular radiating groups. It also occurs as fibrous masses. Its Mohs hardness is 3.5 and it has a specific gravity of 1.88 to 1.90. Optically it is uniaxial negative with indices of refraction of nω = 1.507 and nε = 1.468.

It occurs as a hydrothermal alteration mineral in sulfide ore deposits and geothermal alteration of basalt and tuff. It occurs with zeolites, apophyllite, analcime, calcite, gypsum and pyrite. Thaumasite can also be formed in man-made concrete structures at the detriment of calcium silicate hydrates (C-S-H, with dashes denoting the non-stoichiometry of this hydrated cement phase acting as the "glue" in hardened cement paste) during cement alteration, especially when sulfate attack develops. The reaction consuming the silicates of the "cement glue" can lead to harmful decohesion and softening (more rarely to expansion and cracking) of concrete. Unlike conventional sulfate attack, in which the calcium hydroxide (portlandite) and calcium aluminate hydrates react with sulfates to form gypsum and ettringite (an expansive phase) respectively, in the case of the thaumasite form of sulfate attack (TSA) the calcium silicate hydrates ensuring the cohesion in the hardened cement paste are also destroyed. As a consequence, even concrete containing sulfate-resisting Portland cement may be affected. It was first described in 1878 in Sweden and named from the Greek, "thaumazein", to be surprised, in reference to its unusual composition with carbonate, sulfate and hydroxysilicate anions. The silicate structure of thaumasite is unusual due to the presence of non-tetrahedral silicon in its crystal lattice. Indeed, an atypic octahedral configuration is observed for Si present in thaumasite in the form of hexahydroxysilicate: [Si(OH)6]2−, a species exhibiting a geometry similar to that of the hexafluorosilicate [SiF6]2−.

See also Other calcium silicate hydrate (C-S-H) minerals:

Afwillite Hexafluorosilicic acid, a chemical species with a central hexacoordinated octahedral silicon atom Gyrolite Jennite Stishovite, a rare high-pressure mineral also with hexacoordinated octahedral silica Tobermorite

References

Illustrations

Worked examples

Example 1 — a first encounter with Thaumasite

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

In research: Thaumasite 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 Thaumasite 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: Thaumasite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Calcium minerals, Carbonate minerals, Cement, so understanding it makes those chapters shorter.
In everyday life: Look for Thaumasite 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.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Thaumasite” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Thaumasite in 20 minutes

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

Frequently asked questions

What is Thaumasite in simple terms?

Why does Thaumasite 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 Thaumasite?

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 Thaumasite.