earth science

Khmaralite

Khmaralite 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 Khmaralite rather than just read about it. In short: The mineral khmaralite is a beryllium bearing mineral of the sapphirine group with a chemical formula of (Mg,Al,Fe)16[(Al,Si,Be)12O36]O40. It is most associated with sillimanite, surinamite, musgravite, garnet, and biotite.

Key takeaways

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

Reference excerpt

The mineral khmaralite is a beryllium bearing mineral of the sapphirine group with a chemical formula of (Mg,Al,Fe)16[(Al,Si,Be)12O36]O40. It is most associated with sillimanite, surinamite, musgravite, garnet, and biotite. The known color is a dark greenish blue or a dark green, with a colorless streak. It is transparent with a vitreous luster with no cleavage and a Moh's hardness of 7. It is brittle with an uneven fracture. The calculated density is 3.61 g/cm3. Khmaralite is closely related to sapphirine with a difference in the tetrahedral sequence chain. The tetrahedral sequence chain in sapphirine (Al-Si-Al) is replaced by the sequence Si-Be-Si in khmaralite. Si is replaced by Be on two sites, and Al is replaced by Si on four adjacent sites. This creates an indirect replacement of Al by Be.

Occurrence Khmaralite was found in "Zircon Point" on Khmara Bay, Enderby Land, Antarctica and occurs in a metamorphosed pegmatite. It is named after the area that it was found, which was named in the honor of Ivan Fedorovich Khmara who was a tractor driver that died in Antarctica. The associated minerals with khamralite (sillimanite, surinamite, musgravite, garnet, and biotite) saturated it in BeO, allowing the BeO content to be close to the maximum possible. This is a rare instance, and has not been located elsewhere.

Chemical composition Barbier et al. analyzed khmaralite for constituents other than Li, Be and B with an ARL-EMX electron microprobe using 15 kV accelerating voltage and a 20 nA sample current. Li, Be and B were analyzed with an ARL Ion Microprobe Mass Analyzer (IMMA). It was later found in 1996 while using a Camea ims 4f (Secondary Ion Mass Spectroscopy or SIMS) that the 9Be+ signal was not corrected for the 27Al+ signal in the IMMA data. The IMMA and SIMS BeO contents are respectively, 2.56 and 2.47 weight percent.

Chemical composition by weight percent

(*Fe was analyzed as Fe2+; FeO and Fe2O3 were calculated assuming 28 cations in a formula for 40 O atoms.)

Crystallography Khmaralite has a superstructure that is best described as a doubled sapphirine unit cell because the a axis is in the direction of the tetrahedral chains along which the main cation ordering occurs. There are rows of weak extra reflections that correspond to a doubling of the a axis. These patterns are indexed by the unit cell (P21/c): a = 19.8, b = 14.4, c = 11.2 Å, β = 125°. These were found using electron diffraction and microscopy. The superstructure was also observed in a medium-resolution lattice along the [001] axis. There was also a slight comparison made between the superstructure and the thicker regions of the crystals corresponding to a double100 interplanar spacing equal to 16.1 Å. The powdered x-ray diffraction pattern had a slightly different conclusion but relatively the same as the electron diffraction and microscopy end numbers. The powder pattern was indexed on a monoclinic unit cell and the absences consistent with the P21/c space group were found. The unit cell was similar to the electron diffraction and microscopy: a = 19.794(8), b = 14.367(5), c = 11.320(3) Å, β = 125.49(4)°. But there was an unexplained 0.066 Å difference in the c parameters. The reflections that correspond to the 2xa superstructure are not visible in the powder x-ray pattern of khmaralite. The intensity of the strongest super-cell reflection is only 0.4% of that of the most intense sub-cell reflection. These experiments were then refined, and corrected displaying the notable 2xa superstructure of khmaralite.

Distinguishing from sapphirine-2M The major differences between khmaralite and sapphirine-2M are the presence of a 2xa superstructure and the larger count of Be at one tetrahedral site. Khmaralite and sapphirine-2M cannot be distinguished by optical properties alone because the internal effects of Be on the crystal structure are covered by the effect of Fe substitution for Mg and Al. But the presence of 2 wt% or more of BeO indicates a likely advocate for khmaralite. Confirmation is available by using electron diffraction to see if there is a presence of a superstructure.

References

External links Article on Khmaralite, From American Mineralogist

Worked examples

Example 1 — a first encounter with Khmaralite

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

In research: Khmaralite 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 Khmaralite 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: Khmaralite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Inosilicates, Minerals in space group 14, Monoclinic minerals, so understanding it makes those chapters shorter.
In everyday life: Look for Khmaralite 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 Khmaralite in 20 minutes

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

Frequently asked questions

What is Khmaralite in simple terms?

Why does Khmaralite 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 Khmaralite?

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 Khmaralite.