earth science

Pearceite

Pearceite 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 Pearceite rather than just read about it. In short: Pearceite is one of the four so-called "ruby silvers", pearceite Cu(Ag,Cu)6Ag9As2S11, pyrargyrite Ag3SbS3, proustite Ag3AsS3 and miargyrite AgSbS2. It was discovered in 1896 and named after Dr Richard Pearce (1837–1927), a Cornish–American chemist and metallurgist from Denver, Colorado.

Key takeaways

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

Reference excerpt

Pearceite is one of the four so-called "ruby silvers", pearceite Cu(Ag,Cu)6Ag9As2S11, pyrargyrite Ag3SbS3, proustite Ag3AsS3 and miargyrite AgSbS2. It was discovered in 1896 and named after Dr Richard Pearce (1837–1927), a Cornish–American chemist and metallurgist from Denver, Colorado.

Nomenclature Pearceite and polybasite are closely related minerals that form the pearceite-polybasite series. Originally pearceite was thought to be an arsenic analogue of polybasite Cu(Ag,Cu)6Ag9Sb2S11, and was called arsenpolybasite, and one polytype of polybasite was called antimonpearceite. Arsenpolybasite was found to represent two different polytypes, arsenpolybasite-221 and arsenpolybasite-222. In modern usage the old name pearceite is replaced by the polytype name pearceite-Tac, arsenpolybasite-221 by pearceite-T2ac, arsenpolybasite-222 by pearceite-M2a2b2c and antimonpearcite by polybasite-Tac. Pearceite-Tac forms a series with polybasite-Tac.

Crystallography and Structure Two structural varieties, trigonal and monoclinic, are known. The trigonal variety crystallizes in the hexagonal scalenohedral class 3m (3 2/m), space group P3m1 (P3 2/m 1). The monoclinic variety crystallises in the prismatic 2/m class, space group C2/m. Unit cell parameters

Monoclinic variety: There are two formula units per unit cell (Z = 2), the lengths of the sides of the unit cell are a = 12.64 Å, b = 7.29 Å, c = 11.90 Å and the angle between the c and a directions is β = 90.0°. Trigonal variety: There is one formula unit per unit cell (Z = 1), two of the sides are of equal length a = 7.3876 Å and the third side, parallel to the threefold axis, is c = 11.8882 Å. The crystal structure consists of sheets stacked along the c axis. The arsenic atoms form isolated (As,Sb)S3 pyramids, copper cations link two sulfur atoms and the silver cations are found in various sites with low coordination numbers, 2,3 and 4, as is usually the case with silver.

Properties Pearceite is often granular and massive; crystals are short, tabular pseudohexagonal prisms with bevelled edges, showing triangular striations on faces parallel to the plane containing the a and b axes, and rosettes of such crystals, to 3 cm across. The mineral is black, and in polished section it is white with very dark red internal reflections. It has a black to reddish black streak and a metallic luster, generally opaque, but translucent in very thin fragments. It is biaxial with a very high refractive index of 2.7 and maximum birefringence δ also 2.7. Dispersion of the optic axes is relatively strong. Reflected light anisotropism is the property of appearing to change color when viewed under crossed polarised light in a reflected light microscope. Pearceite exhibits moderate anisotropism, often dark violet. The color in reflected plane polarised light is white, with very dark red internal reflections and very weak pleochroism in air, fair in oil. Reflectivity in air at 540 nm is about 30%. It is not fluorescent. Pearceite is a brittle mineral that breaks with a conchoidal to irregular fracture. It is soft, with hardness only 3, the same as calcite. The silver content gives it a high specific gravity of 6.15, the highest of the ruby silvers. Cleavage is either absent or poor. The mineral is neither magnetic nor radioactive.

Occurrence and associations The type locality is the Mollie Gibson Mine, Aspen, Aspen District (Roaring Fork District), Pitkin County, Colorado, where the mineral occurs in hydrothermal deposits formed at low to medium temperatures, associated with acanthite, tetrahedrite, native silver, proustite, quartz, baryte and calcite. Type material is lodged at Yale University, New Haven, Connecticut, references 3.4270, 3.4292, 3.4293, and at The Natural History Museum, London, England, reference 84843.

References

External links Nikon: Introduction to Polarized Light Microscopy Olympus: Polarized Light Microscopy Archived 2009-02-21 at the Wayback Machine Geological Microscopes A virtual Polarizing Microscope

Illustrations

Worked examples

Example 1 — a first encounter with Pearceite

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

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

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

Frequently asked questions

What is Pearceite in simple terms?

Why does Pearceite 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 Pearceite?

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 Pearceite.