earth science

Taranakite

Taranakite 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 Taranakite rather than just read about it. In short: Taranakite is a hydrated alkali iron-aluminium phosphate mineral with the chemical formula (K,Na)3(Al,Fe3+)5(PO4)2(HPO4)6·18 H2O. It forms from the reaction of clay minerals or aluminous rocks with solutions enriched in phosphate derived from bat or bird guano or, less commonly, from bones or other organic matter.

Key takeaways

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

Reference excerpt

Taranakite is a hydrated alkali iron-aluminium phosphate mineral with the chemical formula (K,Na)3(Al,Fe3+)5(PO4)2(HPO4)6·18 H2O. It forms from the reaction of clay minerals or aluminous rocks with solutions enriched in phosphate derived from bat or bird guano or, less commonly, from bones or other organic matter. Taranakite is most commonly found in humid, bat inhabited caves near the boundary of guano layers with the cave surface. It is also found in perennially wet coastal locations that have been occupied by bird colonies. The type location, and its namesake, the Sugar Loaf Islands off Taranaki, New Zealand, is an example of a coastal occurrence. Taranakite forms small white, pale yellow, or gray crystals, which are typically found in pulverulent nodular aggregates, or crusts. Taranakite crystallizes in the hexagonal system, and is noted as having the longest crystallographic axis of any known mineral: the c-axis of the taranakite unit cell is 9.505 nanometers long.

Occurrence Taranakite was first described in 1866 by James Hector and William Skey. The material had been found by H. Richmond on the Sugar Loaf Islands of Taranaki, New Zealand (in the vicinity of 39.049086°S 174.027708°E / -39.049086; 174.027708), as thin yellowish-white amorphous seams in fissures within trachytic rocks. Within the taranakite, dark yellow-brown seams were observed and thought to be wavellite. Modern X-ray analysis later showed this inclusion to be vashegyite (Al11(PO4)9(OH)6)·38H2O).

Taranakite itself was initially mistaken for wavellite. Physical differences—its relative softness and ease of fusibility—led Skey, the colonial New Zealand Government analyst, to undertake quantitative chemical analysis which identified the mineral as a double hydrous phosphate of aluminia and potash, with some replacement of aluminium with ferric iron. This identified it as a new mineral species – the first to be discovered in New Zealand. Hector and Skey identified bird guano as the most likely source of the phosphate required to form taranakite, and speculated on possible advantages of its use in making superphosphate, owing to the absence of carbonate and relatively small amounts of aluminium. Such industrial use was never realized owing to the limited distribution of taranakite. Taranakite was rediscovered in two cave locations, and given two new names. In 1894, Armand Gautier described a mineral which he called minervite from caves at Grotte de Minerve in Hérault, France and argued that it formed from decomposing guano and animal remains reacting with clays. He experimentally justified this by reacting ammonium phosphate with gelatinous aluminium oxide, iron carbonate, and limestone. These reactions yielded a minervite-like compound, and iron and calcium phosphates similar to what he observed in the caves. In 1904 Eugenio Casoria found a mineral under a guano layer at Monte Alburno, Italy which he called palmerite. These two minerals were later identified through X-ray powder diffraction as taranakite and discredited in favor of taranakite by historical priority. Further occurrences of taranakite include:

Misserghin, Algeria (as minervite) (1895) Jenolan Caves, Australia (as minervite) (1898) No guano deposits are present in the caves; phosphatization is believed to occur from river water containing organic matter penetrating the cave. Réunion, Indian Ocean (as minervite) (1910) Within a basalt cave in the Saint-Paul district Islas Leones, Patagonia (1933) Associated with a penguin colony Pig Hole Cave, near Blacksburg, Virginia (1954) A limestone cave. Taranakite occurs as a powder near the contact of bat guano and hair with clay, and within fractures in brecciated clay. This was the first discovery of taranakite in the United States. Onino-Iwaya cave, Hiroshima Prefecture, Japan (1975) As a powder associated with gypsum within clay sediments, no more than three centimeters below the surface in areas of bat guano deposits. Mezesse Cave near Yaoundé, Cameroon Coralloid speleothems of regularly alternating taranakite and opal microlayers in a granitic cave. The regular layering of taranakite was explained as the seasonal effect of leaching of guano and flow of clay from upper parts of the cave during the rainy season. Cook's Head Rock and Green Island, Otago, New Zealand (2003) Occurring with leucophosphite as microcrystalline aggregates in jointed and brecciated basalt. Little blue penguins on Green Island and gulls on Cooks Head Rock are believed to be the main guano source. The coastal occurrences, in New Zealand and Patagonia, occur at high latitudes supporting the necessity of humid conditions for the formation of taranakite. In the tropics, rather than taranakite, the minerals that form from guano-derived phosphatization of igneous rocks are variscite (AlPO4·2H2O), metavariscite (AlPO4·H2O), barrandite ((Al,Fe3+)PO4·2H2O), strengite and phosphosiderite (Fe3+PO4·2H2O).

Presence in soils Taranakite is observed to form in the reaction zone of fertilizers. Potassium-taranakite (synonymous with taranakite) or ammonium-taranakite (where the alkali cations are replaced by ammonium) may form in acidic soils treated with potassium or ammonium-containing phosphate-fertilizers. The formation of taranakites, which are relatively insoluble, can act to reduce the bioavailability of phosphorus, potassium, and nitrogen if formed. This can both hinder plant growth in initial stages by reducing the available cations, and also aid in the long run by extending the presence of these nutrients.

Structure

Taranakite crystallizes in the hexagonal crystal system (hexagonal scalenohedral, 32/m) with the space group R3c. The unit cell dimensions are a = 870.25 pm and c = 9505 pm, enclosing a volume of 6.234 nm3. The c-axis is the longest of any known mineral.

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Taranakite

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

In research: Taranakite 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 Taranakite 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: Taranakite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Aluminium minerals, Cave minerals, Geology of New Zealand, so understanding it makes those chapters shorter.
In everyday life: Look for Taranakite 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 Taranakite in 20 minutes

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

Frequently asked questions

What is Taranakite in simple terms?

Why does Taranakite 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 Taranakite?

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 Taranakite.