earth science

Shigaite

Shigaite 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 Shigaite rather than just read about it. In short: Shigaite is a mineral with formula NaAl3(Mn2+)6(SO4)2(OH)18·12H2O that typically occurs as small, hexagonal crystals or thin coatings. It is named for Shiga Prefecture, Japan, where it was discovered in 1985.

Key takeaways

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

Reference excerpt

Shigaite is a mineral with formula NaAl3(Mn2+)6(SO4)2(OH)18·12H2O that typically occurs as small, hexagonal crystals or thin coatings. It is named for Shiga Prefecture, Japan, where it was discovered in 1985. The formula was significantly revised in 1996, identifying sodium as a previously unknown constituent.

Description

Shigaite occurs as hexagonal tabular crystals up to 2 cm (0.79 in) in size or as thin films and coatings. The mineral can be yellow, burnt orange, brown or black in color. Shigaite occurs in metamorphosed deposits of manganese ore and is the Mn2+ analogue of motukoreaite.

Structure Shigaite consists of oxycation sheets of [AlMn2+2(OH)6]1+ intercalated with oxyanion sheets of [Na(H2O)6{H2O}6(SO4)2]3−. Linkage between the sheets and within the oxyanion sheet results largely through hydrogen bonding.

History Shigaite was discovered in 1985 in the Ioi Mine, Shiga Prefecture, Japan. The original study, published in the journal Neues Jahrbuch für Mineralogie, Monatshefte, identified the formula as Al4Mn7(SO4)2(OH)22·8H2O. The formula was significantly revised in 1996 using a sample from the N'Chwaning Mine, South Africa. Sodium, discovered to be a component of shigaite, was not identified in the original study. However, an unidentified volatile had been noted that presumably was a sodium-containing complex.

Distribution As of 2012, shigaite is known from the following sites:

Iron Monarch open cut, South Australia, Australia Poudrette quarry, Quebec, Canada Ioi mine, Shiga Prefecture, Japan Wessels Mine, Northern Cape Province, South Africa N'Chwaning Mine, Northern Cape Province, South Africa Homer Mine, Michigan, United States Bengal Mine, Michigan, United States The type material is housed in the National Museum of Natural History in Washington, D.C. as sample 122089.

Association Shigaite has been found associated with the following minerals:

Notes

References

Bibliography Cooper, Mark A.; Hawthorne, Frank C. (February 1996). "The crystal structure of shigaite, (AlMn (super 2+)2 (OH)6)3 (SO4)2 Na(H2O)6 {H2O}6, hydrotalcite-group mineral" (PDF). The Canadian Mineralogist. 34 (1): 91–97. ISSN 0008-4476. Retrieved May 23, 2012.

Further reading Pring, A.; Slade, P. G.; Birch, W. D. (September 1992). "Shigaite from Iron Monarch, South Australia" (PDF). Mineralogical Magazine. 56 (384): 417–419. Bibcode:1992MinM...56..417P. doi:10.1180/minmag.1992.056.384.15. S2CID 140697083. Retrieved April 20, 2012.

Illustrations

Worked examples

Example 1 — a first encounter with Shigaite

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

In research: Shigaite 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 Shigaite 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: Shigaite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aluminium minerals, Manganese(II) minerals, Minerals in space group 148, so understanding it makes those chapters shorter.
In everyday life: Look for Shigaite 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 Shigaite in 20 minutes

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

Frequently asked questions

What is Shigaite in simple terms?

Why does Shigaite 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 Shigaite?

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 Shigaite.