earth science

Phenakite

Phenakite 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 Phenakite rather than just read about it. In short: Phenakite or phenacite is a fairly rare nesosilicate mineral consisting of beryllium orthosilicate, Be2SiO4. Occasionally used as a gemstone, phenakite occurs as isolated crystals, which are rhombohedral with parallel-faced hemihedrism, and are either lenticular or prismatic in habit: the lenticular habit is determined by the development of faces of several obtuse rhombohedra and the absence of prism faces.

Key takeaways

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

Reference excerpt

Phenakite or phenacite is a fairly rare nesosilicate mineral consisting of beryllium orthosilicate, Be2SiO4. Occasionally used as a gemstone, phenakite occurs as isolated crystals, which are rhombohedral with parallel-faced hemihedrism, and are either lenticular or prismatic in habit: the lenticular habit is determined by the development of faces of several obtuse rhombohedra and the absence of prism faces. There is no cleavage, and the fracture is conchoidal. The Mohs hardness is high, being 7.5–8; the specific gravity is 2.96. The crystals are sometimes perfectly colorless and transparent, but more often they are greyish or yellowish and only translucent; occasionally they are pale rose-red. In general appearance the mineral is not unlike quartz, for which indeed it has been mistaken. Its name comes from Ancient Greek: φέναξ, romanized: phénax, meaning "deceiver" due to its close visual similarity to quartz, named by Nils Gustaf Nordenskiöld in 1833.

Largest phenakite

A large phenakite gemstone has been found in Sri Lanka. Found on November 18, 2021, this gemstone weighs 616.9 carats which makes it the largest of its kind. It is owned by a gem dealer from Beruwala, Sri Lanka, and reported to be worth around SL Rs. 1 billion (US $5 million).

Occurrence

Phenakite is found in high-temperature pegmatite veins and in mica-schists associated with quartz, chrysoberyl, apatite and topaz. It has long been known from the emerald and chrysoberyl mine on the Takovaya stream, near Yekaterinburg in the Urals of Russia, where large crystals occur in mica-schist. It is also found with topaz and amazonite in the granite of the Ilmen Mountains in the southern Urals and of the Pikes Peak region in Colorado, US. Additionally in Colorado, phenakite is found in the Mount Antero area with aquamarine, bertrandite, and fluorite. Small, gem grade individual crystals of phenakite showing a prismatic habit are noted in beryl dissolution cavities at the Noumas II Pegmatite, part of the Orange River pegmatite belt in the Northern Cape of South Africa. Large crystals of prismatic habit have been found in a feldspar quarry at Kragerø in Norway. Framont near Schirmeck in Alsace is another well-known locality. Still larger crystals, measuring 12 inches (300 mm) in diameter and weighing 28 lb (13 kg). have been found at Greenwood in Maine, but these are pseudomorphs of quartz after phenakite. For gem purposes the stone is cut in the brilliant form, of which there are two fine examples, weighing 34 and 43 carats (6.8 and 8.6 g), in the British Museum. The indices of refraction are higher than those of quartz, beryl or topaz; a faceted phenakite is consequently rather brilliant and may sometimes be mistaken for diamond.

References

Illustrations

Worked examples

Example 1 — a first encounter with Phenakite

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

In research: Phenakite 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 Phenakite 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: Phenakite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Beryllium minerals, Gemstones, Minerals in space group 148, so understanding it makes those chapters shorter.
In everyday life: Look for Phenakite 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.

Affiliate

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

How to study Phenakite in 20 minutes

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

Frequently asked questions

What is Phenakite in simple terms?

Why does Phenakite 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 Phenakite?

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 Phenakite.