earth science

Sheldrickite

Sheldrickite 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 Sheldrickite rather than just read about it. In short: Sheldrickite is a sodium calcium carbonate fluoride mineral, named in honor of George M. Sheldrick, former Professor of Crystallography at the University of Göttingen in Germany.

Key takeaways

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

Reference excerpt

Sheldrickite is a sodium calcium carbonate fluoride mineral, named in honor of George M. Sheldrick, former Professor of Crystallography at the University of Göttingen in Germany. Sheldrick is the creator of SHELX computer program widely used for the analysis of crystal structures. Determination of the structure of this mineral required the software's capability of handling twinned crystals.

Occurrence Sheldrickite is a rare mineral found in Mont Saint-Hilaire, Canada. Mont Saint-Hilaire is an alkaline intrusive complex and one of the ten Monteregian Hills. A series of plutons is aligned along the St. Lawrence Valley for almost 150 km eastward from Oka to Megantic. Sheldrickite is closely associated with shortite (Na2Ca2(CO3)), with the crystals being found in a cavity between shortite crystals. Sheldrickite also occurs as flakes in thin seams between crystals of shortite. Sheldrickite is thought to be formed in a late-stage hydrothermal infilling. The associated species of Sheldrickite include pectolite, microcline, arfvedsonite, aegirine, polylithionite, calcite, fluorite and minor molybdenite, leucosphenite, thenardite, thermonatrite, sphalerite, galena, schairerite and kogarkoite.

Physical and optical properties Sheldrickite has 2 distinct habits, one occurs as a 1x1x2 mm aggregate of blocky twined crystals with 0.1x0.1x0.1 mm individuals. The second habit occurs as a radiating thin white silky flakes to fibrous masses up to 2 mm wide. Each habit was established as the same species by X-ray diffraction, infrared spectroscopy, and electron-microprobe data. This mineral is colorless to white, it has a white streak and a vitreous luster. It has a brittle uneven fracture and has good {001} parting. It has no fluorescence and has a Mohs hardness of 3, and a density of 2.86 +-0.04 g/cm2.

Crystallography Sheldrickite is Trigonal-pyramidal with the space group being P32. This mineral has an axial ratio of 1:2.24025, with cell dimensions of a = 6.718 Å, c = 15.05 Å, Z = 3 Å; V = 588.23 Å. The precession photographs show sheldrickite to be hexagonal with a diffraction symmetry of 6/mmm, with space-group choices P6222 and P6422. After the solution of the crystal structure, it was shown that the actual symmetry of sheldrickite is trigonal, space group P32 and the pseudohexagonal symmetry is due to merohedral twinning.

Chemical composition

Structure The structure of sheldrickite has four large-cation sites, but only two distinct types of polyhedral. The Sodium (Na) polyhedron, with its 8-fold coordination, fits the compressed octahedron that is modified by the removal of one edge. The compressed axis corresponds to the Na-F bonds, where the removed edge results in the four longer bonds in the polyhedron. Each of these three Calcium (Ca) sites has a similar stereochemistry and a similar polyhedron, in the nine-fold coordination. The polyhedron fits within the irregular trigonal prism, with the three Fluorine (F) atoms defining the equatorial plane and the other six ligands and the upper and lower face of the prism. The crystal structure of sheldrickite is layered on (001). In sheldrickite, there are two layers of different composition: (1) Na(CO3)2·H2O, and (2) CaF. The pseudo-m planes are positioned through the Na(CO3)2·H2O layers, and the pseudo-2-fold axis along [100] is at 0,0,0. The carbonate layer is the mixed-layer type and the standing on end (CO3) groups are not in a separate layer but occur with the cations and H2O groups. Sheldrickite structure is a combination of the bastnäsite - (Ce) structure with segregated large-cation layers and (CO3) layers, and the cebaite - (Ce) structure with integrated large-cation and (CO3) groups in the same layer. Sheldrickite has a segregated large-cation layer and an integrated large cation - (H2O) - (CO3) layer.

References

Worked examples

Example 1 — a first encounter with Sheldrickite

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

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

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

Frequently asked questions

What is Sheldrickite in simple terms?

Sheldrickite is a sodium calcium carbonate fluoride mineral, named in honor of George M. Sheldrick, former Professor of Crystallography at the University of Göttingen in Germany.

Why does Sheldrickite 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 Sheldrickite?

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 Sheldrickite.