Fairchildite

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Fairchildite
General and classification
chemical formula
  • K 2 CO 3 • CaCO 3
  • K 2 Ca (CO 3 ) 2
  • K 2 Ca [CO 3 ] 2 (> 550 ° C)
Mineral class
(and possibly department) 		Carbonates and nitrates - carbonates without additional anions; without H 2 O
System no. to Strunz
and to Dana 		5.AC.20 ( 8th edition : Vb / A.05)
03/14/03/01
Crystallographic Data
Crystal system hexagonal
Crystal class ; symbol dihexagonal-dipyramidal; 6 / m  2 / m  2 / m
Space group P 6 3 / mmc (No. 194)Template: room group / 194
Lattice parameters a  = 5.294  Å ; c  = 13.355 Å
Formula units Z  = 2
Physical Properties
Mohs hardness 2.5
Density (g / cm 3 ) 2.45 (measured); 2.45 (calculated)
Cleavage good after {0001}
Break ; Tenacity no information in the literature; no information in the literature
colour colorless (crystals); light gray to bluish gray (aggregates)
Line color White
transparency transparent
shine Glass gloss
Crystal optics
Refractive indices n ω  = 1.533
n ε  = 1.498
Birefringence δ = 0.035
Optical character uniaxial negative
Pleochroism none
Other properties
Chemical behavior hygroscopic in air; Conversion into butschliite and later into calcite

Fairchildite is a very rarely occurring mineral from the mineral class of " carbonates and nitrates " (formerly carbonates, nitrates and borates ). It crystallizes in the hexagonal crystal system with the idealized chemical composition of K 2 Ca (CO 3 ) 2 - is thus seen a chemically potassium - calcium - carbonate .

The mineral is found in the form of microscopic, {0001} plate-like crystals with a six-sided outline and typically dense, stony mineral aggregates .

Fairchildite is formed from melted wood ash from trees that have been struck by lightning and partially burned, e.g. B. Hemlocks . Its type localities are Grand Canyon National Park in Arizona , USA , and Coolin in Kaniksu National Forest ( coordinates of Kaniksu National Forest ), Bonner County , Idaho , USA.

Etymology and history

Since the 1920s of the last century, stones ("clinker") of a special kind have been found in the trunks of partially burned trees in many places in the forests of the western United States. Obviously, these stones did not resemble those found in the regional soil , and most of the finds led to various guesses as to their origin. As early as 1929, several researchers such as the chemists Duane T. Englis and WN Day and the botanist Raymond Kienholz had correctly described the nature and origin of these stones.

“... there was' no justification for the assumption that the clinkers were of meteoric origin 'as had been supposed by some, but rather that' the peculiar rock-like character of the clinkers is probably due to the collection of a large quantity of ash in the hollow snag, followed by occasional wetting from rain and finally a fusion of the mass, during a later vigorous burning of the surrounding wood '… ”

“There is' no justification for assuming that the clinkers are of meteoric origin ', as some have suggested, but' that the peculiar rock-like character of the clinkers is probably due to the accumulation of a large amount of ash in the hollow tree stumps, followed by occasional wetting by Rain and finally a fusion of the mass during a later violent burning of the surrounding wood '... "

- Duane T. Englis & WN Day : The composition of peculiar clinkers found after forest fires (1929)

When examining two of these clinker-like stones from the Grand Canyon National Park and the Kaniksu National Forest , the US mineralogists Charles Milton and Joseph Meyer Axelrod identified two phases which subsequently turned out to be new minerals. In 1947 these minerals were first described scientifically by the two scientists in the American science magazine "The American Mineralogist" as Fairchildite ( English Fairchildite ) and Bütschliite ( English Bütschliite ). They named the former mineral after USGS chemist John Gifford Fairchild (1882–1965) in recognition of his help in the analytical description of the new minerals.

The type of material for Fairchildite is under the catalog numbers 105675 and 105676 (Donation USGS , 1948 via Charles Milton) in the collection of the Smithsonian Institution belonging to National Museum of Natural History in Washington, DC , USA , kept. Further type material can be found in the same collection under catalog number 162622.

Due to its discovery and first description before 1959, Fairchildite is one of the minerals that the IMA calls grandfathered and does not have an IMA number.

classification

In the 8th edition of the mineral classification according to Strunz , the Fairchildit belonged to the common mineral class of "carbonates, nitrates and borates" and there to the department of "carbonates", where together with Burbankit , Bütschliit , Carbocernait , Eitelit , Nyerereit , Sahamalith and Shortit die "Eitelit-Sahamalith-Gruppe" with the system no. Vb / A.05 within the sub-section "Anhydrous carbonates without foreign anions ".

In the last revised and updated Lapis mineral directory in 2018 , which is still based on this outdated system of Karl Hugo Strunz out of consideration for private collectors and institutional collections , the mineral was given the system and mineral number. V / B.05-020 . In the "Lapis system" this corresponds to the section "Anhydrous carbonates [CO 3 ] 2− , without foreign anions ", where Fairchildite, together with juangodoyite , Eitelite, Nyerereit, Gregoryite , Zemkorite , Bütschliit and Shortite , form the unnamed group V / B. 05 forms.

The 9th edition of Strunz's mineral systematics , which has been in force since 2001 and updated by the International Mineralogical Association (IMA) until 2009, assigns Fairchildite to the “carbonates and nitrates” class, which has been reduced by the borates, and then to the “carbonates without additional” class Anions; without H 2 O “. This is further subdivided according to the group affiliation of the cations involved , so that the mineral can be found according to its composition in the subsection "Alkali and alkaline earth carbonates", where the unnamed group with the system no. 5.AC.20 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Fairchildite, like the outdated Strunz system, to the common class of “carbonates, nitrates and borates” and there to the department of “carbonates”. Here he is together with Zemkorit in the " Fairchilditgruppe " with the system no. 03/14/03 within the sub-section “Anhydrous carbonates with a compound formula A + B 2+ (CO 3 ) 2 ”.

Chemism

Analyzes of almost pure natural fairchildite material apparently do not exist. Identification depends on the correspondence of other properties with those of synthetic material. A 60 µm multiphase inclusion in the core of a magnetite crystal from the phoscoritic carbonatite mined by the “Loolekop Mine” near Phalaborwa, South Africa, has an average composition (five measured values) of 38.54% K 2 O; 23.15% CaO; 1.47% FeO and 0.63% Na 2 O. The idealized formula K 2 Ca (CO 3 ) 2 for Fairchildite requires 23.5% CaO; 39.5% K 2 O and 37.0% CO 2 .

The official IMA formula for Fairchildite is given as K 2 Ca (CO 3 ) 2 . The Strunz formula K 2 Ca [CO 3 ] 2 follows the IMA-compliant formula, but here, as usual, the anion group is summarized in square brackets.

The only combination of elements K – Ca – C – O, as can be found in the official formula of the IMA for Fairchildite, contains only Bütschliite among the currently known minerals (as of 2020) besides Fairchildite.

From a chemical point of view, Fairchildite is the K-dominant analogue of the Na-dominated zemkorite, with which it probably forms a mixed crystal row , as the empirical formulas of the current species suggest.

Crystal structure

Fairchildite crystallizes in the hexagonal crystal system in the space group P 6 3 / mmc (space group no. 194) with the lattice parameters a = 5.294  Å and c = 13.355 Å as well as two formula units per unit cell . Template: room group / 194

The crystal structure of fairchildite is similar to that of nyerereite. The potassium and calcium atoms are statistically distributed over the two Me positions, the Me (1) position being coordinated seven times and the Me (2) position eight times, resulting in the following formula: K 2 [7] Ca [8] (CO 3 ) 2 . One of the crystallographically different CO 3 groups lies parallel to (0001), three are inclined at 69 ° to it.

The chemical compound K 2 Ca (CO 3 ) 2 is dimorphic , in addition to the hexagonal Fairchildite there is also the trigonal Bütschliit. They can be viewed as the high pressure (Fairchildite) and low pressure (Bütschliite) polymorphs of K 2 Ca (CO 3 ) 2 .

properties

morphology

Fairchildite forms microscopic, {0001} plate-like crystals with a six-sided outline and typically dense, stony mineral aggregates, which were referred to as "clinker" in the original publication. According to Paul Ramdohr and Hugo Strunz, Fairchildit forms “the finest fibers”. In the slag deposits of the Braubach lead and silver smelter, fairchildite was found in the form of needle-like crystals formed in radial directions (then accompanied by calcite and langite ) or aggregated in a tangled manner (then without parageme minerals).

The "clinker" of the original description both contain inclusions of charcoal or blackish carbonaceous areas. The “clinker” from the “Kaniksu National Forest” is dense and stony, colored light gray and streaked with splinter-like cracks, where it breaks into sharp-edged fragments with a diameter of one or two centimeters. There is evidence of flow in the material as it melts, some deep, rounded holes can be attributed to the escape of gases during the melting. Twenty years after the find, the “clinker” shows little or no signs of decay or change. The “clinker bricks” from the “Grand Canyon National Park” vary in appearance from a hard bluish-gray stone mass inside to a crumbly white porcelain-like crust. They seem to disintegrate (disintegrate) very slowly.

physical and chemical properties

Fairchildite is colorless (crystals) to light gray to bluish gray (aggregates), while its line color is indicated as white. The surfaces of the transparent crystals of Fairchildite show a characteristic glass-like sheen . Fairchildite has a medium-high refraction ( n ε  = 1.498; n ω  = 1.533) and a medium birefringence (δ = 0.035) corresponding to this glass gloss . In transmitted light, the uniaxial negative fairchildite is colorless and shows no pleochroism .

Fairchildite has good cleavage properties based on {0001}. There are no data on tenacity and breakage for the mineral. Fairchildite has a Mohs hardness of 2.5 and is one of the soft to medium-hard minerals that, with the appropriate crystal size, like the reference minerals gypsum (hardness 2), can be scratched with a fingernail or calcite (hardness 3) with a copper coin. The measured density for Fairchildite is 2.446 g / cm³, the calculated density is 2.45 g / cm³.

Fairchildite does not show fluorescence in either long-wave or short-wave UV light (254 nm) .

The mineral is hygroscopic in the air and slowly transforms into Bütschliit. An atmosphere saturated with water accelerated the transformation. In the event of further exposure, Bütschliit absorbs hygroscopic water and dissolves incongruently with the formation of calcite. Bütschliite can be converted back into Fairchildite by heating it in a closed but unsealed carbon crucible at 704 ° C.

Education and Locations

At its two type localities, the “Grand Canyon National Park” and the “Kaniksu National Forest”, Fairchildite is formed from melted wood ash from trees that have been struck by lightning and partially burned. According to Raymond Kienholz, the trees in which the stones were found were mostly the West American hemlock ( Tsuga heterophylla ), but also the common Douglas fir and occasionally the coastal fir ( Abies grandis ), noble fir ( Abies nobilis ) and possibly also the western white pine ( Pinus monticola ). According to him, the stones only formed in rotten heartwood, mostly in hemlocks infected by the fungus Echinodontium tinctorum ("Indian Paint Fungus") and in Douglas firs infected by the fungus Trametes pini . In areas where the Indian mushroom was not widespread, no clinkers were observed after forest fires. Kienholz also noted that similar clinkers had been observed from a different origin, namely in the fireplaces of kettles that burned clean hemlock sawdust. In the Phoenix area of ​​Arizona, Fairchildite is formed from the ashes of the Parkinsonia microphylla tree .

Interest in the "clinker" was renewed in 1944 when Herbert Ernest Gregory, geologist for the United States Geological Survey , found one in Grand Canyon National Park at a height of 23 m in a coastal fir tree that had previously been struck by lightning , referred found "clinker" to the Chemical Laboratory of the Geological Survey. In a letter to Clarence S. Ross, USGS petrologist , Professor Gregory wrote: “Although it has been determined to be molten limestone, the presence of such a large piece of limestone on the top of a tree cannot be explained ... I am rather inclined to regard the material as molten ash. ”One of the erroneous ideas about the genesis of these“ clinkers ”is that they are meteorites, molten limestone or pathological growths in living trees or that they are caused by excessive evaporation of sap or that they are ashes melted together.

Further educational opportunities are:

  • in alkaline carbonatite complexes ("Loolekop Mine" near Phalaborwa, South Africa)
  • in slag (e.g. dump of lead and silver smelter Braubach near Koblenz)
  • in the combustion products (> 600 ° C) of biomass and agricultural waste
  • in synthetic glass and cement clinker of different compositions

Minerals accompanying the Fairchildite at its type locality are butschliite and calcite. In the Phoenix area in Maricopa Co., Arizona, USA, calcite, CaO, Bütschliite and periclase with traces of other potassium-containing salts were found in the fresh ashes in addition to fairchildite . After light rains, a brittle crust of calcite formed with variable amounts of fairchildite, sylvine , kalicinite , calcite containing magnesium, magnesite, the compound K 2 CO 3 · 1.5H 2 O and arcanite . Further exposure to heavy rains resulted in a product consisting mainly of calcite, magnesium-containing calcite and periclase. Ash collected two years after its formation consisted largely of calcite and magnesium-containing calcite, with little nesquehonite . In the "Loolekop Mine" near Phalaborwa, South Africa, fairchildite was found as an inclusion in centimeter-sized magnetite crystals accompanied by dolomite , geikielite - ilmenite or picroilmenite , phlogopite , brucite , witherite and halite . In the slag deposits of the Braubach lead and silver smelter, fairchildite is accompanied by calcite and langite .

As a very rare mineral formation, Fairchildite is only known from a few localities or in a small number of stages. So far (as of 2020), the mineral has been described by around 15 sites in addition to its type locality. The type localities of the Fairchildit are Grand Canyon National Park in Arizona , and Coolin in Kaniksu National Forest , Bonner County , Idaho , both in the USA .

Other locations for Fairchildit are:

Locations from Austria and Switzerland are therefore unknown.

use

Fairchildite has no economic importance and is only of interest to the collector of minerals.

See also

literature

  • Charles Milton, Joseph Meyer Axelrod: Fused wood-ash stones: Fairchildite K 2 CO 3 · CaCO 3 , buetschliite 3K 2 CO 3 · 2CaCO 3 · 6H 2 O and calcite, CaCO 3 , their essential components . In: The American Mineralogist . tape 32 , no. 11/12 , 1947, pp. 607–624 (English, rruff.info [PDF; 1.3 MB ; accessed on January 17, 2020]).
  • Mary Emma Mrose, Harry J. Rose, John W. Marinkenko: Synthesis and properties of fairchildite and buetschliite: their relation in wood-ash stone formation . In: GSA Special Papers (Geological Society of America Abstracts for 1966: Abstracts of papers submitted for six meetings with the Society was associated) . tape 101 , 1966, pp. 146 (English, limited preview in Google Book search).
  • Fairchildite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 62 kB ; accessed on January 17, 2020]).
  • Charles Palache , Harry Berman , Clifford Frondel : Fairchildite . In: The System of Mineralogy . of James Dwight Dana and Edward Salisbury Dana Yale University 1837-1892. 7th edition. II (Halides Nitrates, Borates, Carbonates, Sulfates, Phosphates, Arsenates, Tungstates, Molybdates etc.). John Wiley & Sons, New York 1951, ISBN 0-471-19272-4 , pp. 222 (English, first edition: 1892).
  • Friedrich Klockmann : Klockmann's textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke , Stuttgart 1978, ISBN 3-432-82986-8 , pp. 577 (first edition: 1891).
  • Hans Jürgen Rösler : Textbook of Mineralogy . 4th revised and expanded edition. German publishing house for basic industry (VEB), Leipzig 1987, ISBN 3-342-00288-3 , p. 719 .

Web links

Individual evidence

  1. ↑ a b c d e f g h i j k l m n Charles Milton, Joseph Meyer Axelrod: Fused wood-ash stones: Fairchildite K 2 CO 3 · CaCO 3 , buetschliite 3K 2 CO 3 · 2CaCO 3 · 6H 2 O and calcite, CaCO 3 , their essential components . In: The American Mineralogist . tape 32 , no. 11/12 , 1947, pp. 607–624 (English, rruff.info [PDF; 1.3 MB ; accessed on January 17, 2020]).
  2. ↑ a b c d Franz Pertlik: Structural investigations of synthetic fairchildite, K 2 Ca (CO 3 ) 2 . In: Journal of Crystallography . tape 157 , no. 3/4 , 1981, p. 199–205 , doi : 10.1524 / zkri.1981.157.3-4.199 (English, rruff.info [PDF; 294 kB ; accessed on January 17, 2020]).
  3. ↑ a b c d e f g h i j k l m n o p q r Fairchildite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 62  kB ; accessed on January 17, 2020]).
  4. ↑ a b c d e f g h Fairchildite. In: mindat.org. Hudson Institute of Mineralogy, accessed January 17, 2020 .
  5. ↑ a b c Malcolm Back, William D. Birch, Michel Blondieau and others: The New IMA List of Minerals - A Work in Progress - Updated: November 2019. (PDF 1752 kB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, November 2019, accessed January 17, 2020 .
  6. ↑ a b c d e Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  291 (English).
  7. ↑ a b c d Charles Palache , Harry Berman , Clifford Frondel : Fairchildite . In: The System of Mineralogy . of James Dwight Dana and Edward Salisbury Dana Yale University 1837-1892. 7th edition. II (Halides Nitrates, Borates, Carbonates, Sulfates, Phosphates, Arsenates, Tungstates, Molybdates etc.). John Wiley & Sons, New York 1951, ISBN 0-471-19272-4 , pp.  222 (English, first edition: 1892).
  8. ↑ a b c d David Barthelmy: Fairchildite Mineral Data. In: webmineral.com. Retrieved January 17, 2020 (English).
  9. ↑ a b Duane T. Englis, WN Day: The composition of peculiar clinkers found after forest fires . In: Science . tape 69 , no. 1797 , 1929, pp. 605–606 , doi : 10.1126 / science.69.1797.605 (English).
  10. ^ Raymond Kienholz: On the Occurrence of Rock-Like Clinkers in Burning Snags . In: Journal of Forestry . tape 27 , no. 5 , 1929, pp. 527-531 , doi : 10.1093 / jof / 27.5.527 (English).
  11. ↑ Catalog of Type Mineral Specimens - F. (PDF 73 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed January 11, 2020 .
  12. ↑ Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties. Status 03/2018 . 7th, completely revised and supplemented edition. Weise, Munich 2018, ISBN 978-3-921656-83-9 .
  13. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF 1703 kB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed September 25, 2019 .
  14. ↑ a b c Victor V. Sharygin, Liudmila M. Zhitova, Elena N. Nigmatulina, E. Yu. Zhitov: Fairchildite in carbonatite of the Phalaborwa Igneous complex . In: Geochimica et Cosmochimica Acta . tape 73 , no. 13 , 2009, p. A1205 (English, researchgate.net [PDF; 227 kB ; accessed on January 17, 2020]).
  15. ^ Minerals with K-Ca-C-O. In: mindat.org. Hudson Institute of Mineralogy, accessed January 17, 2020 .
  16. ↑ a b c d e Mary Emma Mrose, Harry J. Rose, John W. Marinkenko: Synthesis and properties of fairchildite and buetschliite: their relation in wood-ash stone formation . In: GSA Special Papers (Geological Society of America Abstracts for 1966: Abstracts of papers submitted for six meetings with the Society was associated) . tape 101 , 1966, pp. 146 (English, limited preview in Google Book search).
  17. ^ Friedrich Klockmann : Klockmanns textbook of mineralogy . Ed .: Paul Ramdohr , Hugo Strunz . 16th edition. Enke , Stuttgart 1978, ISBN 3-432-82986-8 , pp.  577 (first edition: 1891).
  18. ↑ a b c Günter Schnorrer-Koehler, Wolfgang David: The lead and silver smelter Braubach and their dump minerals . In: Lapis . tape 16 , no. 1 , 1991, p. 38-49 .
  19. ↑ a b Laurence AJ Garvie: Mineralogy of paloverde (Parkinsonia microphylla) tree ash from the Sonoran Desert: A combined field and laboratory study . In: The American Mineralogist . tape 101 , no. 7 , 2016, p. 1584–1595 , doi : 10.2138 / am-2016-5571 (English).
  20. ↑ a b Victor V. Sharygin, Liudmila M. Zhitova, Elena N. Nigmatulina: Fairchildite K 2 Ca (CO 3 ) 2 from phoscorites in Phalaborwa, South Africa: the first occurrence in alkaline carbonatite complexes . In: Russian Geology and Geophysics . tape 52 , no. 2 , 2011, p. 208–219 , doi : 10.1016 / j.rgg.2010.12.015 (English, researchgate.net [PDF; 2.7 MB ; accessed on January 17, 2020]).
  21. ↑ MJ Fernández Llorente, José Maria Murillo Laplaza, Ricardo Escalada-Cuadrado, JE Carrasco García: Ash behavior of lignocellulosic biomass in bubbling fluidized bed combustion . In: Fuel . tape 85 , no. 9 , 2006, p. 1157–1165 , doi : 10.1016 / j.fuel.2005.11.019 (English).
  22. ↑ Despina Vamvuka, D. Zografos: Predicting the behavior of ash from agricultural wastes during combustion . In: Fuel . tape 83 , no. 14/15 , 2004, pp. 2051–2057 , doi : 10.1016 / j.fuel.2004.04.012 (English).
  23. ↑ a b c Hugo Bolio Arceo, FP Glasser: Fluxing reactions of sulfates and carbonates in cement clinkering II. The system CaCO 3 –K 2 CO 3 . In: Cement and concrete research . tape 25 , no. 2 , 1995, p. 339-344 , doi : 10.1016 / 0008-8846 (95) 00019-4 (English).
  24. ↑ Localities for Fairchildite. In: mindat.org. Hudson Institute of Mineralogy, accessed January 17, 2020 .
  25. ↑ a b c List of localities for Fairchildite from the Mineralienatlas and Mindat (accessed on January 17, 2020)