Nyerereit

from Wikipedia, the free encyclopedia
Nyerereit
General and classification
other names
  • Natrofairchildit
  • IMA 1963-014
chemical formula
  • Na 2 Ca (CO 3 ) 2
  • Na 2 Ca [CO 3 ] 2
  • (Na 0.82 K 0.18 ) 2 Ca (CO 3 ) 2
  • (Na, K) 2.60 Ca 0.93 (CO 3 ) 2
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.10 ( 8th edition : Vb / A.05)
03/14/04/01
Crystallographic Data
Crystal system orthorhombic
Crystal class ; symbol orthorhombic-pyramidal; mm 2
Space group Cmc 2 1 (No. 36)Template: room group / 36
Lattice parameters a  = 5.044  Å ; b  = 8.809 Å; c  = 12.743 Å
Formula units Z  = 4
Twinning always polysynthetically parallel [001]
Physical Properties
Mohs hardness ≈ 2.5
Density (g / cm 3 ) 2.541 (measured); 2.42 (calculated)
Cleavage no information in the literature; indistinct after the base (natrofairchildit)
Break ; Tenacity no information in the literature
colour colorless, white (natrofairchildit)
Line color White
transparency transparent to semi-transparent
shine Glass gloss (natrofairchildit)
Crystal optics
Refractive indices n α  = 1.5112
n β  = 1.5333
n γ  = 1.5345
Birefringence δ = 0.0233
Optical character biaxial negative
Axis angle 2V = 29 ° (measured); 2V 28 ° (calculated)
Pleochroism none
Other properties
Chemical behavior stable in the air, but easily soluble in warm water
Special features orange luminescence (natrofairchildit); bright orange cathodoluminescence

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

Nyerereit is a rock-forming mineral and can be found in the form of crystals ( porphyroclasts ) or phenocrysts in a natrocarbonatite . The crystals are flat-paneled according to (001) and have a obtuse-rectangular cross-section, whereby the smallest crystals can also have "dovetail-shaped" terminations.

The type locality of Nyerereits 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

Julius Kambarage Nyerere - namesake for the Nyerereit

Nyerereit was discovered by the British geologist John Barry Dawson in the carbonatite lavas (lengaite) that erupted from the Oldoinyo Lengai volcano, Tanzania, between March 1960 and September 1965. An initial brief description was published in the English science magazine Nature , and a further work on this appeared in the Bulletin of Volcanology. It was recognized as a new mineral by Duncan McKie of the "Department of Mineralogy and Petrology" at the University of Cambridge in the United Kingdom and by Charles Milton (then United States Geological Survey , Washington, DC ), both of whom were employed independently by John Barry Dawson Provided material worked. Based on preliminary mineralogical and crystallographic data from Charles Milton and Blanche Ingram (both US Geological Survey), the mineral was submitted to the Commission on New Minerals of the International Mineralogical Association (IMA), which designated it in 1963 as IMA 1963-014 new mineral recognized. The mineral name Nyerereit has also been approved by the IMA. Except for a short version (abstract) in the program for the Annual Meeting 1968 of the Geological Society of America by Charles Milton, an actual scientific first description of this mineral was not made until 1977.

For this reason, Duncan McKie and EJ Frankis published substantial corrections and additions to the preliminary description presented by Milton & Ingram in an extensive article in the German science magazine “Zeitschrift für Kristallographie”. This article is the first published report on the mineralogy and crystallography of the Nyerereit. Charles Milton and Blanche Ingram named the mineral after the Tanzanian politician Julius Kambarage Nyerere (1922-1999), who at the time of the discovery of the mineral was the state president and head of government of the "Republic of Tanganyika " (and later of the United Republic of Tanzania ).

The type of material for Nyerereite is under the catalog numbers 113544 (Donation Charles Milton, United States Geological Survey , 1967) and 162608 (Donation Mary Emma Mrose, 1985) in the collection of the Smithsonian Institution belonging to National Museum of Natural History in Washington, DC , USA , kept.

Probably identical with Nyerereit is a mineral described in 1971 - without recognition by the IMA - which came from the alkali rock-ultrabasite massif "Vuoriyärvi" ( Russian массив Вуориярви ), North Karelia , Murmansk Oblast, Kola Peninsula, Russia for which the name “Natrofairchildit” was chosen as the Na-dominant analog of the K-dominated Fairchildite. Although significantly more physical properties were described in this work than in the article by Duncan McKie and EJ Frankis, the name Natrofairchildit has been discarded by Nyerereit for reasons of priority.

classification

In the 8th edition of the mineral classification according to Strunz , the Nyerereit 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 , Fairchildit , 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 Nyerereit, together with juangodoyite , Eitelite , Gregoryite , Fairchildite , Zemkorite , Bütschliit and Shortit, form 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 Nyerereit to the class of "carbonates and nitrates" reduced by the borates and to the category 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 subsection "Alkali and alkaline earth carbonates", where, together with Zemkorite, the unnamed group with the system no. 5.AC.10 forms.

Also the systematics of minerals according to Dana , which is mainly used in the English-speaking area , assigns the Nyerereit like the outdated Strunz'sche systematics to the common class of "carbonates, nitrates and borates" and there in the department of "carbonates". Here he is to be found as the only member of the unnamed group 14.03.04 within the sub-section “ Anhydrous carbonates with a compound formula A 2+ B 2+ (CO 3 ) 2 ”.

Chemism

A wet chemical analysis by Blanche Ingram on clear, homogeneous Nyerereit grains showed 22.2% CaO; 2.0% SrO; 0.6% BaO; 26.2% Na 2 O; 7.9% K 2 O; 39.0% CO 2 ; 2.1% SO 3 ; 0.23% F; 0.42% Cl; 0.8% H 2 O; (−O = (F, Cl) 2 corresponds to 0.2%, the sum is 101.2%). On the basis of three oxygen atoms, the empirical formula (Na 2.03 K 0.48 ) [(C 1.12 S 0.06 ) (Cl 0.01 F 0.01 ) O 3.38 ( OH) 0.2 ] · (Ca 0.94 Sr 0.08 Ba 0.01 ) CO 3 or idealized CaCO 3 · 1.2 Na 2 CO 3 . Average content of 14 microprobe analysis of Nyerereit phenocrystals from lavas from the October 9, 1992 eruption showed 26.11% CaO; 2.27% SrO; 0.28% BaO; 23.56% Na 2 O; 6.96% K 2 O; 39.18% CO 2 (calculated from stoichiometry); 1.07% SO 3 ; 0.13% Cl; (−O = (F, Cl) 2 corresponds to 0.03%, sum 100.00%). The ideal composition Na 2 Ca (CO 3 ) 2 requires 30.08% Na 2 O; 27.21% CaO and 42.71% CO 2 . Analyzes on “Natrofairchildit” from the alkaline rock-ultrabasite massif “Vuoriyärvi” showed 25.61 CaO%; 0.85% SrO; 0.44% BaO; 29.46% Na 2 O; 1.35% K 2 O and 41.93% CO 2 (total 99.64%), which corresponds to the empirical formula (Na, K) 2.60 Ca 0.93 (CO 3 ) 2 .

The official formula of the IMA for the Nyerereit is given as Na 2 Ca (CO 3 ) 2 . The Strunz formula, Na 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 Na – Ca – C – O among the currently known minerals (as of 2019) shows, besides Nyerereit, only shortite , Na 2 Ca 2 (CO 3 ) 3 , and zemkorite , Na 2 Ca (CO 3 ) 2 , as well as the three unnamed phases Unnamed (Na-Ca Carbonate I) , Na 4 Ca (CO 3 ) 3 , Unnamed (Na-Ca Carbonate II) , Na 2 Ca 3 (CO 3 ) 4 , and Unnamed (Na-Ca Carbonate III) , Na 2 Ca 4 (CO 3 ) 5 .

The chemical compound Na 2 Ca (CO 3 ) 2 is dimorphic and could even be trimorphic, since the nature of the “natrofairchildite” from the alkaline rock-ultrabasite massif “Vuoriyärvi” is still not fully understood. Nyerereit is the orthorhombic dimorph to the hexagonal zemkorite. The high temperature modification (> 340 ° C) of Nyerereite, β-Nyerereit, is hexagonal like Zemkorite.

Crystal structure

Nyerereit crystallizes in the orthorhombic crystal system in the space group Cmc 2 1 (space group no. 36) with the lattice parameters a = 5.044  Å ; b = 8.809 Å and c = 12.743 Å as well as four formula units per unit cell . Template: room group / 36

The high-temperature structure (β-Nyerereit) crystallizes in the hexagonal crystal system in the space group P 6 3 mc (space group no. 186) with the lattice constants a = 5.05  Å and c = 12.85 Å as well as two formula units per unit cell . Template: room group / 186

The crystal structure of the β-Nyerereits consisting of Na [6 + 3] - polyhedra , NaO 6 - octahedra and CaO 6 - hexagons , represented by CO 3 are interconnected groups. The CO 3 groups are arranged in parallel (0001). The crystal structure of the nyerereite is related.

properties

morphology

In the lengaite lavas at the type locality, Nyerereit forms crystals up to 1 mm in size, which, accompanied by rounded or oval gregoryite phenocrystals up to several millimeters in diameter, “swim” in a matrix of mainly fluorite and sylvine . The Nyerereit crystals are flat tabular according to (001) with well developed surfaces of the basic pinacoid {001} - but have no actual surfaces in the [001] zone. They have a obtuse-rectangular cross-section, whereby the smallest crystals can also have “dovetail-shaped” terminations. The smallest dimension is typically in the direction of [001]. Sections parallel or sub-parallel to [001] thus have a short length and, with the standard thickness of the thin section , show interference colors that reach up to second-order blue; such sections do not provide any evidence of twinning. Sections more or less parallel to (001), however, show first-order gray tones and characteristically hatched twins, so that the twin individuals cancel out at 60 ° to one another. Without exception, Nyerereit forms polysynthetic twins in parallel [001]. Nyerereit can also be found in the form of inclusions in the gregoryite, which is interpreted as the separation of a solid mixed crystal.

Natriumkarbonatit lavas that from 23 to 30 July 2000 at the Ol Doinyo Lengai from Hornitos erupted T37B and T49b, unusual contain sylvite - and fluorite microcrystals and fluorite Nyerereite adhesions. The latter are relatively coarse-grained and have grainy textures that indicate slow rates of crystallization compared to those of their subaeric host slaves. It is believed that the fluorite microcrystals arise from the fragmentation of the fluorite-Nyerereit clasts.

“Natrofairchildit” from the alkaline rock-ultrabasite massif “Vuoriyärvi” was only found there in depths of ≥ 70 m in burbankite - calcite veins. It forms platy single crystals up to 2 mm in size, which have no surfaces, but show polysynthetic twinning parallel to cleavage. There are also fan-shaped crystal aggregates. The mineral decomposes easily and is replaced by powdery calcite.

Nyerereite (and nahcolite ) were also used as micro and nano inclusions in diamonds from the area around Juína in Brazil identified. They form a carbonatitic mineral paragenesis in diamond, which may have originated in the lower mantle and / or the transition zone to the upper mantle .

physical and chemical properties

The crystals of nyerereite or “natrofairchildite” are colorless or white (natrofairchildite). Their line color , however, is always white. The surfaces of the transparent to semi-transparent crystals of natofairchildite show a characteristic glass-like sheen . According to this glass gloss, Nyerereit has a medium-high light refraction ( n α  = 1.5112; n β  = 1.5333; n γ  = 1.5345) and a medium-high birefringence (δ = 0.0233). In transmitted light, the biaxial negative Nyerereit is colorless and shows no pleochroism . Depending on the cutting position, blue interference colors of the 2nd order or gray interference colors of the 1st order can be seen.

No cleavage properties are given for Nyerereit in the literature . "Natrofairchildit" has an indistinct cleavage after the basic pinacoid {001}. There is no information on breakage and tenacity for the mineral. Nyerereit has a Mohs hardness of ≈ 2.5 and is thus one of the soft minerals that, like the reference mineral gypsum (hardness 2), could just about be scratched with a fingernail if the crystal size was appropriate. The measured density for Nyerereit is 2.541 g / cm³, the calculated density is 2.42 g / cm³.

"Natrofairchildit" shows UV light an orange luminescence . Nyerereit has a light orange-colored cathodoluminescence .

Nyerereit is stable in the air, but easily soluble in warm water

Education and Locations

Ol Doinyo Lengai - type locality for the Nyerereit. Individual hornitos are easy to see. The photo was taken on February 12, 2006.

Nyerereit can be found at its type locality as a rock-forming mineral in a natro carbonatite . Accompanying minerals of nyerereite are gregoryite, ferrous alabandin , halite , sylvin , fluorite , calcite , witherite , sellaite , potassium-containing neighborite and khanneshite . Although the majority of Nyerereit phenocrystals are homogeneous, they occasionally contain small inclusions of gregoryite, fluoroapatite, monticellite and sphalerite in sizes of up to 50 μm. In rare cases, Nyerereit microcrystals in the base mass of natrocarbonatite are covered by barium-containing Nyerereit.

As a rare mineral formation, Nyerereit 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 around 20 sites in addition to its type locality. The type locality of the Nyerereits 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.

Nyerereit was also found in Tanzania at the Kerimasi volcano , Monduli district , also in the Arusha region .

Further localities for Nyerereit are:

Locations in Austria and Switzerland are not known.

use

If you disregard the interest of the mineral-collecting community in this mineral, Nyerereit is economically completely insignificant.

See also

literature

  • Duncan McKie, EJ Frankis: Nyerereite: A new volcanic carbonate mineral from Oldoinyo Lengai, Tanzania . In: Journal of Crystallography . tape 145 , no. 1-2 , 1977, pp. 73–95 , doi : 10.1524 / zkri.1977.145.1-2.73 (English, rruff.info [PDF; 1,2 MB ; accessed on December 4, 2019]).
  • Nyerereite . 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; 65 kB ; accessed on December 4, 2019]).
  • 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 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 f g Nyerereite. In: mindat.org. Hudson Institute of Mineralogy, accessed December 4, 2019 .
  3. ↑ a b c d e f g h i j Nyerereite . 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; 65  kB ; accessed on December 4, 2019]).
  4. ↑ a b c d e f g 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.  290 (English).
  5. ↑ a b c d e f g h i j k l m n o p q r s Duncan McKie, EJ Frankis: Nyerereite: A new volcanic carbonate mineral from Oldoinyo Lengai, Tanzania . In: Journal of Crystallography . tape 145 , no. 1-2 , 1977, pp. 73–95 , doi : 10.1524 / zkri.1977.145.1-2.73 (English, rruff.info [PDF; 1,2 MB ; accessed on December 4, 2019]).
  6. ↑ a b c d e f g h i j k l Yuri L. Kapustin: Natrofairchildite . In: Mineralogiya karbonattiov (Mineralogy of Carbonatites) . 1st edition. Izdat. "Nauka", Moscow 1971, ISBN 978-0-86249-363-9 , pp. 181-183 (Russian).
  7. ↑ a b c d e f Luke LY Chang , Robert Andrew Howie , Jack Zussman : Rock-forming minerals Vol. 5B: Non-silicates: Sulphates, Carbonates, Phosphates and Halides . 2nd Edition. Longman, London 1996, ISBN 0-582-30093-2 , pp.  282–287 (English, limited preview in Google Book Search - first edition: 1961).
  8. ^ A b David Barthelmy: Nyerereite Mineral Data. In: webmineral.com. Retrieved December 4, 2019 .
  9. ↑ a b c 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).
  10. ^ John Barry Dawson: Sodium Carbonate Lavas from Oldoinyo Lengai, Tanganyika . In: Nature . tape 195 , 1962, pp. 1075-1076 , doi : 10.1038 / 1951075a0 (English).
  11. ^ John Barry Dawson: The geology of Oldoinyo Lengai . In: Bulletin of Volcanology . tape 24 , no. 1 , 1962, pp. 349-387 , doi : 10.1007 / BF02599356 (English).
  12. ^ Charles Milton: The "natro-carbonatite" lava of Oldionyo Lengai, Tanzaria . In: Geological Society of America Program Annual Meeting . tape 1968 , 1968, pp. 202 (English, rruff.info [PDF; 65 kB ; accessed on December 4, 2019]).
  13. ↑ Catalog of Type Mineral Specimens - N. (PDF 61 kB) In: docs.wixstatic.com. Commission on Museums (IMA), December 12, 2018, accessed August 29, 2019 .
  14. ↑ a b c d e f Michael Fleischer, George Y. Chao, AkIro Kato: New mineral names . In: American Mineralogist . tape 60 , no. 5-6 , 1975, pp. 485–489 (English, minsocam.org [PDF; 624 kB ; accessed on December 4, 2019]).
  15. ↑ 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 .
  16. ↑ 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 .
  17. ^ 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).
  18. ↑ Minerals with Na, Ca, O, C. In: mindat.org. Hudson Institute of Mineralogy, accessed December 4, 2019 .
  19. ↑ a b c 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]).
  20. ↑ 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).
  21. ^ Roger H. Mitchell: Sylvite and Fluorite Microcrysts, and Fluorite-Nyerereite Intergrowths from Natrocarbonatite, Oldoinyo Lengai, Tanzania . In: Mineralogical Magazine . tape 70 , no. 1 , 2006, p. 103-114 , doi : 10.1180 / 0026461067010316 (English).
  22. ^ Felix V. Kaminsky, Richard Wirth, Stanislav S. Matsyuk, A. Schreiber, Rainer Thomas: Nyerereite and nahcolite inclusions in diamond: evidence for lower-mantle carbonatitic magmas . In: Mineralogical Magazine . tape 73 , no. 5 , 2009, p. 797–816 , doi : 10.1180 / minmag.2009.073.5.797 (English, https://www.researchgate.net/publication/225646076 researchgate.net [PDF; 746 kB ; accessed on November 27, 2019]).
  23. ↑ a b 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).
  24. ^ 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).
  25. ^ Roger H. Mitchell: Mineralogy of Stalactites Formed by Subaerial Weathering of Natrocarbonatite Hornitos at Oldoinyo Lengai, Tanzania . In: Mineralogical Magazine . tape 70 , no. 4 , 2006, p. 437-444 , doi : 10.1180 / 0026461067040344 (English).
  26. ↑ Localities for Nyerereite. In: mindat.org. Hudson Institute of Mineralogy, accessed December 4, 2019 .
  27. ↑ a b c d List of localities for Nyerereit in the Mineralienatlas and Mindat (accessed on December 4, 2019)