earth science

Penroseite

Penroseite 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 Penroseite rather than just read about it. In short: Penroseite is a rare selenide mineral with formula (Ni,Co,Cu)Se2. It has a gray-steel color and black streak with a hardness of 3.

Key takeaways

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

Reference excerpt

Penroseite is a rare selenide mineral with formula (Ni,Co,Cu)Se2. It has a gray-steel color and black streak with a hardness of 3. It is an isometric mineral, 2/m3. Penroseite was first discovered in 1925 in a Bolivian rhyolite. It was named for Richard Penrose (1863–1931), an economic geologist. Penroseite is a rare mineral found in the Pacajake mine in Bolivia. It was discovered in 1925. It used to be found in fissure veins in the extrusive igneous rhyolite rock. It is considered as a member of the pyrite group from the perspective of its structure, with a cubic space group (Bayliss, 1989). Penroseite makes extensive solid solutions with other minerals. For example, penroseite can be a result of alteration process of many selenides, such as olsacherite Pb2(SO4)(SeO4). Olsacherite forms very sparingly in well formed crystal covering the walls of the external side of the small cracks (Hurlbut, 1969). Another mineral related to penroseite is piretite. It occurs as an alteration product of uraninite and primary selenium-bearing sulfides, such as penroseite. Piretite forms as crusts in association with an orange masuyite-like U-Pb oxide on the surface of uraninite samples (Vochten, 1996).

Composition Its composition have mixture of elements, some of them are primary elements such as nickel (Ni), copper (Cu), cobalt (Co), and selenium (Se) that make with each other a substitution in different amounts. The secondary elements, that might be found in penroseite due to the occurrence process or the environment in which the mineral was deposited, are silver (Ag), mercury (Hg), and lead (Pb)(Gordon, 1926). Lead, that was considered as a part of the composition when it was discovered, found to be in the composition due to the intergrowth of clausthalite PbSe and is not a primary element(Earley, 1950). Penroseite has a high content of selenium like no other mineral, and as a result it was reported as the first nickel selenide mineral discovered (Gordon, 1926).

Physical properties Penroseite is a massive mineral. It can have radiating, columnar, or granular structure (Gordon, 1926). It shows a dull lead-gray to steel-gray color with a black streak. It has a metallic luster and thought to have a weak chemical bonding and that what makes it with a low hardness around 3 (Earley, 1950). When it reacts with HNO3 or KCN, a fumes tarnish to brown are resulted. But if it reacts with HCl, FeCl3, or HgCl2, it does not show any activity (Gordon, 1926).

Geologic occurrence The mineral is found in the Pacajake mine in Colquechaca, 150 km (93 mi) southeast of Oruro Department, Bolivia. Penroseite comes from the vicinity, and forms in fissure veins in rhyolite. It is not found in-situ, rather only in float (loose rocks) from undiscovered veins which have either been eroded away or remain hidden in the mountain above (Gordon, 1926).

Structure Penroseite has a cubic space group Pa3 (Bayliss, 1989). It was found that it behaves like isotropic crystals in which light passes through all directions with the same speed, which is strong enough to conclude that it is isometric (Bannister, 1937). Since it is isometric, all axes equal the same value. This value, due to different measurement techniques, ranges between 6.001 and 6.017 angstrom (Earley, 1950). Since there is no brief description on penroseite's structure, it almost have the same Pyrite subgroup structure (Earley, 1950). The type of bonds found in the Pyrite group is covalent, but not in penroseite. For example, pyrite FeS2, which has the same structure as penroseite and is thought to have similar coordination, has one Fe atom surrounded by six atoms of S, an octahedral coordination. On the other hand, the S atom is surrounded by 4 Fe atoms in a tetrahedral configuration (Jaffe, 1988). This might give an idea of how the atoms are arranged in penroseite in the absence of a real structure determination due to the undefined composition of the mineral.

References

Illustrations

Worked examples

Example 1 — a first encounter with Penroseite

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

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

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

Frequently asked questions

What is Penroseite in simple terms?

Penroseite is a rare selenide mineral with formula (Ni,Co,Cu)Se2. It has a gray-steel color and black streak with a hardness of 3.

Why does Penroseite 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 Penroseite?

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 Penroseite.