Gregoryite

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Gregoryite
Gregorite.JPG
Rounded gregoryite crystals ( porphyroclasts ) in a natrocarbonatite from Ol Doinyo Lengai , Tanzania . Thin section photo , crossed polar, magnification about ten times. Field of view: 2 mm.
General and classification
other names

IMA 1981-045

chemical formula
  • Na 2 (CO 3 )
  • α-Na 2 [CO 3 ] (> 490 ° C)
  • (Na 2 , K 2 , Ca, □) CO 3
  • (Na 2 , K 2 , Ca) CO 3
  • (Na, K) 2 CO 3
Mineral class
(and possibly department) 		Carbonates and nitrates - carbonates without additional anions; without H 2 O
System no. to Strunz
and to Dana 		5.AA.10
01/14/02/02
Crystallographic Data
Crystal system hexagonal
Crystal class ; symbol dihexagonal-pyramidal; 6 mm
Space group P 6 3 mc (No. 186)Template: room group / 186
Lattice parameters a  = 5.215  Å ; c  = 5.645 Å
Formula units Z  = 2
Physical Properties
Mohs hardness 3
Density (g / cm 3 ) calculated: 2.27 to 2.31
Cleavage available
Break ; Tenacity no information in the literature
colour brown, milky white, colorless to tan
Line color White
transparency translucent to translucent
shine Glass gloss
Crystal optics
Refractive indices n ω  = 1.517
n ε  = 1.467
Refractive index n  = 1.46 to 1.49 (calculated)
Birefringence δ = 0.050
Optical character uniaxial
Axis angle 2V = 0 ° to 10 °
Other properties
Chemical behavior soluble in water, unstable under normal atmospheric conditions
Special features dark brown-orange cathodoluminescence

Gregoryite is a very rare 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 Na 2 (CO 3 ), and is therefore chemically seen a sodium - carbonate .

Gregoryite is found in the form of rounded crystals ( porphyroclasts ) or phenocrysts in a natrocarbonatite . The type locality of Gregoryits is the world's only active carbonatite - volcano Ol Doinyo Lengai ( coordinates of the volcano Ol Doinyo Lengai ) in the district of Ngorongoro in the region Arusha in northern Tanzania .

Etymology and history

John Walter Gregory - namesake for the Gregoryite

In 1980, John Gittins and Duncan McKie described in the Norwegian science magazine "Lithos" published article about alkaline carbonatite - magmas in general and the carbonatite lavas of the volcano "Ol Doinyo Lengai" in particular a mineral which they rounded in thin sections in the form of Had discovered grains. After the required physical and crystallographic properties and chemical composition had been determined, the new mineral was submitted to the International Mineralogical Association (IMA), which recognized it as a new mineral in 1981 under the provisional designation IMA 1981-045. An actually scientific first description of this mineral has never been made, so that apart from the chemical composition hardly any physical and crystallographic properties have been made known for Gregoryite. Chemical analyzes on phenocrystals up to 3 mm in size were presented by Abigail A. Church and Adrian P. Jones in an article published in 1995 in the English scientific magazine "Journal of Petrology".

John Gittins and D. McKie named the mineral after the British explorer and geologist John Walter Gregory (1864-1932), Professor of Geology at the University of Melbourne in Australia and at the University of Glasgow in Scotland , in recognition of his important work on volcanism and Structure of the East African Rift System . The “Gregory Rift” in this system is named after him.

Type material for Gregoryite is not defined.

classification

Since the Gregoryite was only recognized as an independent mineral by the International Mineralogical Association (IMA) in 1981 and the discovery was never fully published, it is not listed in the 8th edition of the Strunz mineral classification, which has been outdated since 1977 .

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.05-040 . In the "lapis Classification", this corresponds to the department "Anhydrous carbonate [CO 3 ] 2- , without foreign anions " where Gregoryit together with Eitelit , Juangodoyit , Nyerereite , Fairchildite , Zemkorite , Bütschliit and Shortite the unnamed group V / B. 05 forms.

The 9th edition of Strunz's mineral systematics, which has been valid since 2001 and updated by the International Mineralogical Association (IMA) until 2009, assigns the Gregoryite to the class of "carbonates and nitrates" reduced by the borates and there into the section of "carbonates without additional ones 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 sub-section "Alkali-Carbonates", where together with Natrite the "Natrite-Gregoryite Group" with the system no. 5.AA.10 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Gregoryite, like the outdated Strunz system, to the common class of “carbonates, nitrates and borates” and there to the “carbonates” division. Here, together with vaterite in the vaterite group with system no. 01/14/02 to be found in the subsection “ Anhydrous carbonates with simple formula A + CO 3 ”.

Chemism

The only microprobe analysis from the first publication on the gregoryite showed 9.10% CaO; 0.66% SrO; 44.87% Na 2 O; 3.95% K 2 O; 36.22% CO 2 (probably calculated from stoichiometry); 4.28% SO 3 ; 1.92% P 2 O 5 ; 0.40% F; 0.60% Cl; (−O = (F, Cl) 2 corresponds to 0.31%, sum 101.93%). Based on three oxygen atoms, the empirical formula (Na 1.56 K 0.10 Ca 0.17 ) Σ = 1.83 CO 3 is calculated .

The official formula of the IMA for the Gregoryite is given as Na 2 (CO 3 ). The Strunz formula, α-Na 2 [CO 3 ], largely follows the IMA-compliant formula, but here, as usual, the anion group is summarized in square brackets.

In 1990 Jörg Keller and Maurice Krafft identified the complex substitution of (CO 3 ) 2− by (SO 4 ) 2− , (PO 4 ) 3− , F - and Cl - in gregoryite and gave the empirical formula Na 1 for the mineral , 74 K 0.1 (Ca, Sr, Ba) 0.16 CO 3 . In 2009, Anatoly N. Zaitsev and colleagues determined concentrations of 5.0–11.9% CaO in gregoryite from lavas from the Ol Doinyo Lengai volcano; 3.4-5.8% SO 3 ; 1.3-4.6% P 2 O 5 ; 0.6-1.0% SrO; 0.1-0.6% BaO; and 0.3-0.7% Cl but no fluorine . Gregoryite typically contains high levels of the trace elements magnesium , lithium and vanadium . They pointed out that it is still unclear whether (SO 4 ) 2− and (PO 4 ) 3− groups as well as Cl - occupy separate structural positions in the gregoryite or merely substitute the (CO 3 ) 2− group . Furthermore, the content of non-formula elements could also be due to the presence of submicroscopic inclusions in gregoryite (nyerereit, fluoroapatite , alabandin and monticellite ). Roger H. Mitchell and Vadim S. Kamenetsky determined 43-106 ppm rubidium , 4255-7275 ppm strontium , 0.3-4.0 ppm yttrium , 0.6-5.1 on gregoryite phenocrystals from natrocarbonatites from the Ol Doinyo Lengai volcano ppm cesium , 1125-7052 ppm barium , 84-489 ppm lithium, 6790-15.860 ppm phosphorus, and 33-155 ppm vanadium.

The sole element combination Na-CO point among the currently known minerals (as of 2019) only Natrit, Na 2 CO 3 , and Natroxalat , Na 2 (C 2 O 4 ), on.

According to Hugo Strunz and Ernest Henry Nickel , Gregoryite, α-Na 2 [CO 3 ], is the hexagonal dimorph to the monoclinic sodium, γ-Na 2 [CO 3 ].

Crystal structure

Gregoryite crystallizes in the hexagonal crystal system in the space group P 6 3 mc (space group no. 186) with the lattice parameters a = 5.215  Å and c = 5.645 Å; as well as two formula units per unit cell . Template: room group / 186

The crystal structure of the gregoryite is still unknown today. However, John Gittins and Duncan McKie have already pointed out that the structure of the gregoryite is a highly disordered structure.

properties

morphology

At its type locality, Gregoryite only forms rounded or oval phenocrystals up to several millimeters in diameter, which “float” in a matrix of mainly fluorite and sylvine . The phenocrystals of the Gregoryite are characterized by an extraordinary heterogeneity of the internal structure. They contain numerous inclusions by Nyerereit, the formation of which is interpreted as the separation of a solid mixed crystal. In addition, there are inclusions of fluorapatite, alabandite and monticellite in the form of tiny crystals of no more than 50 μm as well as inclusions of natrocarbonatite melt in the gregoryite.

physical and chemical properties

Many physical and optical properties of the gregoryite could not be determined due to the small grain size of the material.

The crystals of the gregoryite are brown or milky white or colorless to tan. Their line color is indicated as white. The surfaces of the translucent to transparent crystals show a characteristic glass-like sheen . Corresponding to this glass gloss, Gregoryite has a medium-high refraction ( n ε  = 1.467; n ω  = 1.517) and a medium-high birefringence (δ = 0.050). In transmitted light, the uniaxial gregoryite is pale brown with low relief and shows low order interference colors.

Gregoryite has unspecified cleavage . There is no information on breakage and tenacity for the mineral. Gregoryite has a Mohs hardness of 3 and is one of the medium-hard minerals that, like the reference mineral calcite (hardness 3), could be scratched with a copper coin if the crystal size was appropriate. The calculated density for gregoryite varies between 2.27 g / cm³ and 2.31 g / cm³ depending on the processor.

Gregoryit is neither in the short wave still in the long-wave UV light , a fluorescent . It shows a dark brown-orange-colored cathodoluminescence , which Ulrich Koberski and Jörg Keller attribute to Nyerereit inclusions (with light orange-colored cathodoluminescence), which are arranged as segregated platelets parallel to the cleavage of the gregoryite. The mineral is soluble in water and unstable under normal atmospheric conditions.

Education and Locations

Ol Doinyo Lengai - type locality for the Gregoryite. The photo was taken on February 12, 2006

Gregoryite is found at its type locality as a rock-forming mineral in a natro carbonatite . Accompanying minerals of the gregoryite are nyerereit, ferrous alabandin, halite, sylvin, fuorite, calcite, witherite , sellaite , potassium-containing neighborite and khaneshite in the rock as well as nyerereit, fluorapatite, alabandin and monticellite as inclusions in the gregoryite.

The rounded shape of the gregoryite phenocrystals at the type locality may indicate partial resorption after pressure relief during extrusion . On the other hand, it is not known whether this mineral formed idiomorphic crystals at all - carbonate minerals are often well rounded in their primary stability fields in experimental systems. In general, however, the texture suggests crystallization of Gregoryite (and Nyerereit) prior to extrusion, possible resorption of Gregoryite during extrusion, and subsequent crystallization of the extruded liquid phase as Nyerereit, Gregoryite and Alabandite.

As a very rare mineral formation, Gregoryite is only known from a few localities or in a small number of stages. So far (as of 2019) the mineral has been described by only two other sites in addition to its type locality. The type locality of the Gregoryite is the Ol Doinyo Lengai in the Ngorongoro District in the Arusha region in northern Tanzania . The Ol Doinyo Lengai is the world's only active carbonatite volcano, which, in addition to natrocarbonatite, consists of jacupirangite , nepheline syenite and other rocks. These are extremely alkali-rich lavas with up to 30% Na 2 O. Gregoryite and Sylvin, to a lesser extent, Nyerereit are water-soluble and are responsible for the immediate decomposition and chemical alteration of the natrocarbonatite under atmospheric conditions.

Was Gregoryit also in the Cretaceous , on magnetite mined calcite carbonatite "Bailundo" Bailundo , Province of Huambo , Angola , as well as in the Bultfontein- kimberlite -building "Bultfontein Mine" at Kimberley , District Francis Baard , Province of Northern Cape , South Africa , found.

Locations from Germany , Austria and Switzerland are therefore unknown.

use

Apart from the interest of the mineral-collecting community in this mineral, gregoryite is completely insignificant from an economic point of view.

See also

literature

  • John Gittins, Duncan McKie: Alkalic carbonatite magmas: Oldoinyo Lengai and its wider applicability . In: Lithos . tape 13 , no. 2 , 1980, p. 213-215 , doi : 10.1016 / 0024-4937 (80) 90021-3 .
  • Gregoryite . 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 November 27, 2019]).

Web links

Commons : Gregoryite  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b Malcolm Back, William D. Birch, Michel Blondieau and others: The New IMA List of Minerals - A Work in Progress - Updated: September 2019. (PDF 2692 kB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, September 2019, accessed October 4, 2019 .
  2. ↑ 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.  285 .
  3. ↑ a b c d e f John Gittins, Duncan McKie: Alkalic carbonatite magmas: Oldoinyo Lengai and its wider applicability . In: Lithos . tape 13 , no. 2 , 1980, p. 213-215 , doi : 10.1016 / 0024-4937 (80) 90021-3 (English).
  4. ↑ a b c d Gregoryite. In: mindat.org. Hudson Institute of Mineralogy, accessed November 27, 2019 .
  5. ↑ a b c d e f g h i j k l m n o p q Gregoryite . 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 November 27, 2019]).
  6. ↑ a b c d e f Ulrich Koberski, Jörg Keller: Cathodoluminescence Observations of Natrocarbonatites and Related Peralkaline Nephelinites at Oldoinyo Lengai . In: Keith Bell, Jörg Keller (Eds.): Carbonatite Volcanism: Oldoinyo Lengai and the Petrogenesis of Natrocarbonatites (IAVCEI Proceedings in Volcanology 4) . 1st edition. Springer, Berlin Heidelberg 1995, ISBN 978-3-642-79182-6 , p. 87–99 , doi : 10.1007 / 978-3-642-79182-6 (English, limited preview in the Google book search - Softcover reprint 2012 of hardcover 1st edition 1995).
  7. ↑ a b c d e f g h i j k l m Jan H. Bernard, Jaroslav Hyršl: Minerals and their localities . Ed .: Vandall T. King. 1st edition. Granit, Praha 2004, ISBN 80-7296-039-3 , p. 259 (English).
  8. ^ A b c David Barthelmy: Gregoryite Mineral Data. In: webmineral.com. Retrieved November 27, 2019 .
  9. ↑ a b c d e f g Anatoly N. Zaitsev, Jörg Keller, John Spratt, Teresa E. Jeffries, Victor V. Sharygin: Chemical Composition of Nyerereite and Gregoryite from Natrocarbonatites of Oldoinyo Lengai Volcano, Tanzania . In: Geology of Ore Deposits . tape 51 , no. 7 , 2009, p. 608–616 , doi : 10.1134 / S1075701509070095 (English, https://www.researchgate.net/publication/225646076 researchgate.net [PDF; 746 kB ; accessed on November 27, 2019]).
  10. ↑ John L. Jambor, Nikolai N. Pertsev, Andrew C. Roberts: New mineral names . In: American Mineralogist . tape 81 , no. 2 , 1980, p. 516–520 (English, rruff.info [PDF; 617 kB ; accessed on November 27, 2019]).
  11. ^ A b Abigail A. Church, Adrian P. Jones: Silicate-Carbonate Immiscibility at Oldoinyo Lengai . In: Journal of Petrology . tape 36 , no. 4 , 1995, p. 869-889 , doi : 10.1093 / petrology / 36.4.869 (English).
  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 Jörg Keller, Maurice Krafft: Effusive natrocarbonatite activity of Oldoinyo Lengai, June 1988 . In: Bulletin of Volcanology . tape 52 , no. 8 , 1990, pp. 629-645 , doi : 10.1007 / BF00301213 (English).
  15. ↑ Roger H. Mitchell, Vadim S. Kamenetsky: Trace element geochemistry of nyerereite and gregoryite phenocrysts from natrocarbonatite lava, Oldoinyo Lengai, Tanzania: Implications for magma mixing . In: Lithos . tape 152 , 2012, p. 56–65 , doi : 10.1016 / j.lithos.2012.01.022 (English).
  16. ↑ Minerals with Na, O, C. In: mindat.org. Hudson Institute of Mineralogy, accessed November 27, 2019 .
  17. ↑ Alessandro Da Mommio: Gregoryite Mineral Data and Thin Section Photos. In: alexstrekeisen.it. Retrieved November 27, 2019 .
  18. ^ Roger H. Mitchell, Bruce A. Kjarsgaard: Experimental Studies of the System Na 2 CO 3 -CaCO 3 -MgF 2 at 0.1 GPa: Implications for the Differentiation and Low-temperature Crystallization of Natrocarbonatite . In: Journal of Petrology . tape 52 , no. 7-8 , 2011, pp. 1265-1280 , doi : 10.1093 / petrology / egq069 (English).
  19. ↑ Localities for Gregoryite. In: mindat.org. Hudson Institute of Mineralogy, accessed November 27, 2019 .
  20. ↑ a b List of localities for Gregoryite in the Mineralienatlas and Mindat (accessed on November 27, 2019)