Lavendulan

Key takeaways

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

Reference excerpt

Lavendulan is an uncommon arsenate mineral in the lavendulan group. It is known for its characteristic intense electric blue colour. Lavendulan is very similar to lemanskiite, the analogue trihydrate mineral, to the point of them being considered dimorphs. Lemanskiite is tetragonal, but lavendulan is monoclinic. Lavendulan has the same structure as sampleite, and the two minerals form a series. It is the calcium analogue of zdenĕkite and the arsenate analogue of sampleite. Lavendulan was originally named for the lavender color of the "type" specimen, which has since been determined to be a mixture with no relationship to modern lavendulan. The mineral which is now called lavendulan is not a lavender blue color, and has no relationship to the "type" material from Annaberg. It often contains potassium, cobalt and nickel as impurities.

Unit cell Although lavendulan is monoclinic, the angle β is very close to 90°, making the mineral pseudo-orthorhombic. Most references describe the lavendulan unit cell as an orthorhombic cell containing 8 formula units (Z = 8) but Mindat.org describes a monoclinic unit cell with the length of the c axis halved, and only 4 formula units per unit cell (Z = 4) and space group P21/n. Unit cell parameters are reported as

a = 9.73 Å, b = 41.0 Å, c = 9.85 Å, Z = 8 a = 9.815 Å, b = 40.394 Å, c = 9.99 Å, Z = 8 a = 9.73 Å, b = 41.0 Å, c = 9.85 Å, Z = 8 a = 10.011 Å, b = 19.478 Å, c = 10.056 Å, β = 90.37°, Z = 4

Physical properties Lavendulan is a blue or greenish blue translucent mineral, with a vitreous to waxy luster, satiny in aggregates, and a light blue streak. It occurs as thin botryoidal crusts of minute radiating fibers or as thin rectangular, pseudo-orthorhombic plates, with cleavage in three directions, nearly perfect perpendicular to the b crystal axis, and distinct perpendicular to the a and c axes. Twinning is common. The mineral is brittle, with an uneven fracture. It is quite soft, with hardness 2.5, between gypsum and calcite, and relatively dense; its specific gravity is 3.84, close to that of topaz, and much denser than quartz (specific gravity 2.5 to 2.7). It is easily soluble in hydrochloric acid.

Optical properties The refractive index varies with the direction of propagation of the light, and varies between 1.64 and 1.75. This is quite high, between topaz and ruby. Lavendulan is biaxial (−), and most sources quote values for three refractive indices, for light travelling parallel to the three crystal axes. One source, however, gives lavendulan as nearly uniaxial (−), and quotes only two refractive indices, for the ordinary and extraordinary rays.

Nx = 1.645 Ny = 1.715 Nz = 1.725 Nx = 1.660 Ny = 1.715 Nz = 1.734 Nx = 1.66 Ny = 1.715 Nz = 1.734 Nω = 1.748 Nε = 1.645. Lavendulan is pleochroic, with O = pale blue to pale greenish blue and E = blue to greenish blue.

Environment Lavendulan is a rare secondary mineral in the oxidised zone of some copper-arsenic deposits.

Type locality A lavender blue mineral was discovered in 1837 by Johann F. A. Breithaupt in Annaberg in the Ore Mountains, which is a mountainous region spanning the Czech Republic and Germany. The mineral was named "lavendulan" after the color, and Annaberg was the designated type locality. In 1853, Vogel found a specimen of lavendulan from Jáchymov, also in the Ore Mountains, which was similar in appearance and characteristics to the material from Annaberg. In 1877 Goldsmith examined some specimens of a turquoise blue arsenate of copper from the cobalt deposits of San Juan, Chile, and announced that they were also lavendulan. Nearly fifty years later, In 1924, William Foshag announced that the Chilean material was entirely distinct from that from Jáchymov, and he determined that it was a new mineral, and gave it the name freirinite, from the locality, the Blanca Mine, Freirina, Huasca Province, Atacama Region, Chile. In 1957, however, Claude Guillemin found that lavendulan and freirinite from the type localities gave identical x-ray powder patterns, and freirinite was discredited as a mineral species. Yet another fifty years passed, and in 2007 Geister et al. re-examined Breithaupt's type specimen and found that it was a mixture unrelated to modern lavendulan. The second locality where lavendulan was found is in the Czech Republic, so the type locality of the species was changed to there, namely Jáchymov, Ore Mountains, Karlovy Vary Region. The type material is held at the Mining Academy, Freiberg, Germany, reference 20944.

Occurrences

At the type locality, lavendulan occurs associated with erythrite and a cobalt molybdate originally called pateraite, but now discredited. At San Juan, Chile, it is associated with erythrite, cuprite, malachite and cobaltian wad. At the Cap Garonne Mine, Pradet, Var, Provence-Alpes-Côte d'Azur, France, associated minerals are chalcophyllite, cyanotrichite, parnauite, mansfieldite, olivenite, tennantite, covellite, chalcanthite, antlerite, brochantite and geminite. It also occurs at Tsumeb, Namibia, associated with cuprian adamite, conichalcite, o'danielite, tsumcorite, fahleite, quartz, calcite and gypsum.

References

External links Jmol: http://rruff.geo.arizona.edu/AMS/viewJmol.php?id=07151 Lavendulan photo gallery at Mindat.org

Illustrations

Worked examples

Example 1 — a first encounter with Lavendulan

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

In research: Lavendulan 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 Lavendulan 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: Lavendulan is common in secondary-school and first-year university syllabi. It links to neighbouring topics Arsenate minerals, Calcium minerals, Chloride minerals, so understanding it makes those chapters shorter.
In everyday life: Look for Lavendulan 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.

How to study Lavendulan in 20 minutes

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

Frequently asked questions

What is Lavendulan in simple terms?

Lavendulan is an uncommon arsenate mineral in the lavendulan group. It is known for its characteristic intense electric blue colour.

Why does Lavendulan 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 Lavendulan?

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 Lavendulan.