Taranakite
Encyclopedia
Taranakite is a hydrated alkali
iron
-aluminium
phosphate mineral with chemical formula 35(PO4
)2(HPO4
)6·18H2O
. 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 nanometre
s long.
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°N 174.027708°W), 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 owning 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 minervatie-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:
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).
s. 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.
(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.
The unit cell of taranakite contains six layers of composition 6212, each 13.78 Å thick and separated by layers of water. The rigid structure of each layer is built around 2− groups coordinating three crystallographically distinct aluminium centres, each of which has coordination number
six. Near the middle of each layer, an aluminium ion octahedrally coordinates six HPO42−. Two other oxygens in each hydrogen phosphate group coordinate the other distinct aluminium centres, which in turn are coordinated octahedral to three hydrogen phosphate groups and three water molecules. This structure forms a Al'–P–Al
-axis, with the other distinct aluminium atom offset, and nearly vertically below a PO43− ion.
Taranakite readily loses water when heated. Thermal gravimetric
analysis shows two endothermic water loss events occurring in the ranges 80–140 °C and 140–300 °C corresponding to the sequential loss of five and thirteen water molecules to form francoanellite and a noncrystalline material. Heating to 500 °C results in complete dehydration to form K3Al5P8O29. In the range 562–595 °C crystalline AlPO4 and KAlP2O7 form.
Alkali
In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal element. Some authors also define an alkali as a base that dissolves in water. A solution of a soluble base has a pH greater than 7. The adjective alkaline is commonly used in English as a synonym for base,...
iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
-aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....
phosphate mineral with chemical formula 35(PO4
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
)2(HPO4
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
)6·18H2O
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
. It forms from the reaction of clay minerals or aluminous rocks with solutions enriched in phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
derived from bat or bird guano
Guano
Guano is the excrement of seabirds, cave dwelling bats, and seals. Guano manure is an effective fertilizer due to its high levels of phosphorus and nitrogen and also its lack of odor. It was an important source of nitrates for gunpowder...
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
Type locality (geology)
Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....
, and its namesake, the Sugar Loaf Islands
Sugar Loaf Islands
The Sugar Loaf Islands are a collection of five small uninhabited islands and several sea stacks near Port Taranaki, Taranaki, New Zealand. The largest island, Moturoa Island, covers approximately...
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
Hexagonal crystal system
In crystallography, the hexagonal crystal system is one of the 7 crystal systems, the hexagonal lattice system is one of the 7 lattice systems, and the hexagonal crystal family is one of the 6 crystal families...
, and is noted as having the longest crystallographic axis
Crystal structure
In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...
of any known mineral: the c
Hexagonal crystal system
In crystallography, the hexagonal crystal system is one of the 7 crystal systems, the hexagonal lattice system is one of the 7 lattice systems, and the hexagonal crystal family is one of the 6 crystal families...
-axis of the taranakite unit cell is 9.505 nanometre
Nanometre
A nanometre is a unit of length in the metric system, equal to one billionth of a metre. The name combines the SI prefix nano- with the parent unit name metre .The nanometre is often used to express dimensions on the atomic scale: the diameter...
s long.
Occurrence
Taranakite was first described in 1866 by James HectorJames Hector
Sir James Hector was a Scottish geologist, naturalist, and surgeon who accompanied the Palliser Expedition as a surgeon and geologist...
and William Skey. The material had been found by H. Richmond on the Sugar Loaf Islands
Sugar Loaf Islands
The Sugar Loaf Islands are a collection of five small uninhabited islands and several sea stacks near Port Taranaki, Taranaki, New Zealand. The largest island, Moturoa Island, covers approximately...
of Taranaki, New Zealand (in the vicinity of 39.049086°N 174.027708°W), as thin yellowish-white amorphous seams in fissures within trachytic
Trachyte
Trachyte is an igneous volcanic rock with an aphanitic to porphyritic texture. The mineral assemblage consists of essential alkali feldspar; relatively minor plagioclase and quartz or a feldspathoid such as nepheline may also be present....
rocks. Within the taranakite, dark yellow-brown seams were observed and thought to be wavellite
Wavellite
Wavellite is a phosphate mineral with formula Al323·5H2O.It normally occurs as translucent green radial or spherical clusters.-Discovery and occurrence:...
. 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
Mohs scale of mineral hardness
The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German geologist and mineralogist Friedrich Mohs and is one of several definitions of hardness in...
and ease of fusibility
Fusibility
Fusibility is the ease with which a material will melt. Materials such as solder require a low melting point so that when heat is applied to a joint, the solder will melt before the materials being soldered melt, i.e. high fusibility. On the other hand, firebricks used for furnace linings only...
—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
Ferric
Ferric refers to iron-containing materials or compounds. In chemistry the term is reserved for iron with an oxidation number of +3, also denoted iron or Fe3+. On the other hand, ferrous refers to iron with oxidation number of +2, denoted iron or Fe2+...
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 owning 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
Hérault
Hérault is a department in the south of France named after the Hérault river.-History:Hérault is one of the original 83 departments created during the French Revolution on 4 March 1790...
and argued that it formed from decomposing guano and animal remains reacting with clays. He experimentally justified this by reacting ammonium phosphate
Ammonium phosphate
Ammonium phosphate is the salt of ammonia and phosphoric acid. It has the formula 3PO4 and consists of ammonium cations and phosphate anion. It is obtained as a crystalline powder upon mixing concentrated solutions of ammonia and phosphoric acid, or on the addition of excess of ammonia to the...
with gelatinous aluminium oxide
Aluminium oxide
Aluminium oxide is an amphoteric oxide with the chemical formula 23. It is commonly referred to as alumina, or corundum in its crystalline form, as well as many other names, reflecting its widespread occurrence in nature and industry...
, iron carbonate, and limestone. These reactions yielded a minervatie-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:
- MisserghinMisserghinMisserghin is a city in Boutlélis District, Oran Province, Algeria. Its territory is mainly covered by a salt lake called the Sebkha of Oran.It is the city where the known fruit Clementine were discovered by Father Clément Rodier in 1892.Dr...
, Algeria (as minervite) (1895) - Jenolan CavesJenolan CavesThe Jenolan Caves are caves in the Blue Mountains, New South Wales, Australia; 175 kilometres west of Sydney. They are the most celebrated of several similar groups in the limestone of the country being the oldest discovered open caves in the world...
, 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.
- RéunionRéunionRéunion is a French island with a population of about 800,000 located in the Indian Ocean, east of Madagascar, about south west of Mauritius, the nearest island.Administratively, Réunion is one of the overseas departments of France...
, Indian Ocean (as minervite) (1910)
- Réunion
- Within a basaltBasaltBasalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
cave in the Saint-PaulSaint-Paul, RéunionSaint-Paul is the second-largest commune in the French overseas department of Réunion. It is located on the extreme west side of the island of Réunion.Until 1999, near Saint Paul there was the 428 metres tall mast OMEGA Chabrier transmitter.- Transport :...
district- Islas Leones, PatagoniaPatagoniaPatagonia is a region located in Argentina and Chile, integrating the southernmost section of the Andes mountains to the southwest towards the Pacific ocean and from the east of the cordillera to the valleys it follows south through Colorado River towards Carmen de Patagones in the Atlantic Ocean...
(1933)
- Islas Leones, Patagonia
- Associated with a penguin colony
- Pig Hole Cave, near Blacksburg, VirginiaBlacksburg, VirginiaBlacksburg is an incorporated town located in Montgomery County, Virginia, United States, with a population of 42,620 at the 2010 census. Blacksburg, Christiansburg, and Radford are the three principal jurisdictions of the Blacksburg-Christiansburg-Radford Metropolitan Statistical Area which...
(1954)
- Pig Hole Cave, near Blacksburg, Virginia
- 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, JapanHiroshima Prefectureis a prefecture of Japan located in the Chūgoku region on Honshu island. The capital is the city of Hiroshima.- History :The area around Hiroshima was formerly divided into Bingo Province and Aki Province. This location has been a center of trade and culture since the beginning of Japan's recorded...
(1975)
- Onino-Iwaya cave, Hiroshima Prefecture, Japan
- As a powder associated with gypsumGypsumGypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...
within clay sediments, no more than three centimeters below the surface in areas of bat guano deposits.- Mezesse Cave near Yaoundé, CameroonYaoundé-Transportation:Yaoundé Nsimalen International Airport is a major civilian hub, while nearby Yaoundé Airport is used by the military. Railway lines run west to the port city of Douala and north to N'Gaoundéré. Many bus companies operate from the city; particularly in the Nsam and Mvan neighborhoods...
- Mezesse Cave near Yaoundé, Cameroon
- Coralloid speleothemSpeleothemA speleothem , commonly known as a cave formation, is a secondary mineral deposit formed in a cave. Speleothems are typically formed in limestone or dolostone solutional caves.-Origin and composition:...
s of regularly alternating taranakite and opalOpalOpal is an amorphous form of silica related to quartz, a mineraloid form, not a mineral. 3% to 21% of the total weight is water, but the content is usually between 6% to 10%. It is deposited at a relatively low temperature and may occur in the fissures of almost any kind of rock, being most...
microlayers in a graniticGraniteGranite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
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 RockCook's Head RockCook's Head Rock is a phonolite basalt rock standing on the Chrystall's Beach expanse closely north of the rivermouth settlement Toko Mouth of South Otago, New Zealand. The lower faces of the rock are made up of numerous hexagonal basalt columns suggesting Cook's Head Rock is a former volcanic vent....
and Green IslandGreen Island, New ZealandGreen Island is an island off the coast of Dunedin, New Zealand, also the name of one of the city's suburbs. The suburb is not on the sea — formerly a borough, it took its name from the Green Island bush, uncleared native forest extending from the valley where the town is centred over the hills...
, Otago, New Zealand (2003)
- Cook's Head Rock
- 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
Variscite
Variscite is a hydrated aluminium phosphate mineral |H2O]]). It is a relatively rare phosphate mineral. It is sometimes confused with turquoise; however, variscite is usually greener in color....
(AlPO4·2H2O), metavariscite (AlPO4·H2O), barrandite ((Al,Fe3+)PO4·2H2O), strengite and phosphosiderite (Fe3+PO4·2H2O).
Presence in soils
Tarankaite is observed to form in the reaction zone of fertilizerFertilizer
Fertilizer is any organic or inorganic material of natural or synthetic origin that is added to a soil to supply one or more plant nutrients essential to the growth of plants. A recent assessment found that about 40 to 60% of crop yields are attributable to commercial fertilizer use...
s. Potassium-taranakite (synonymous with taranakite) or ammonium-taranakite (where the alkali cations are replaced by ammonium
Ammonium
The ammonium cation is a positively charged polyatomic cation with the chemical formula NH. It is formed by the protonation of ammonia...
) 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
Bioavailability
In pharmacology, bioavailability is a subcategory of absorption and is used to describe the fraction of an administered dose of unchanged drug that reaches the systemic circulation, one of the principal pharmacokinetic properties of drugs. By definition, when a medication is administered...
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 systemHexagonal crystal system
In crystallography, the hexagonal crystal system is one of the 7 crystal systems, the hexagonal lattice system is one of the 7 lattice systems, and the hexagonal crystal family is one of the 6 crystal families...
(hexagonal scalenohedral, 32/m) with the space group
Space group
In mathematics and geometry, a space group is a symmetry group, usually for three dimensions, that divides space into discrete repeatable domains.In three dimensions, there are 219 unique types, or counted as 230 if chiral copies are considered distinct...
R3c. The unit cell dimensions
Hexagonal crystal system
In crystallography, the hexagonal crystal system is one of the 7 crystal systems, the hexagonal lattice system is one of the 7 lattice systems, and the hexagonal crystal family is one of the 6 crystal families...
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.
The unit cell of taranakite contains six layers of composition 6212, each 13.78 Å thick and separated by layers of water. The rigid structure of each layer is built around 2− groups coordinating three crystallographically distinct aluminium centres, each of which has coordination number
Coordination number
In chemistry and crystallography, the coordination number of a central atom in a molecule or crystal is the number of its nearest neighbours. This number is determined somewhat differently for molecules and for crystals....
six. Near the middle of each layer, an aluminium ion octahedrally coordinates six HPO42−. Two other oxygens in each hydrogen phosphate group coordinate the other distinct aluminium centres, which in turn are coordinated octahedral to three hydrogen phosphate groups and three water molecules. This structure forms a Al'–P–Al
Hexagonal crystal system
In crystallography, the hexagonal crystal system is one of the 7 crystal systems, the hexagonal lattice system is one of the 7 lattice systems, and the hexagonal crystal family is one of the 6 crystal families...
-axis, with the other distinct aluminium atom offset, and nearly vertically below a PO43− ion.
Taranakite readily loses water when heated. Thermal gravimetric
Thermogravimetry
Thermogravimetry is a branch of physical chemistry, materials research, and thermal analysis...
analysis shows two endothermic water loss events occurring in the ranges 80–140 °C and 140–300 °C corresponding to the sequential loss of five and thirteen water molecules to form francoanellite and a noncrystalline material. Heating to 500 °C results in complete dehydration to form K3Al5P8O29. In the range 562–595 °C crystalline AlPO4 and KAlP2O7 form.