Keno plumbo microlite

from Wikipedia, the free encyclopedia
Keno plumbo microlite
General and classification
other names

IMA 2015-007a

chemical formula (Pb, □) 2 Ta 2 O 6 [□, (OH), O]
Mineral class
(and possibly department) 		Oxides and hydroxides
System no. to Strunz
and to Dana 		4.DH.15 ( 8th edition : IV / C.18)
02/08/02/03 (as plumbomicrolite)
Crystallographic Data
Crystal system cubic
Crystal class ; symbol cubic hexakisoctahedral; 4 / m  3  2 / m
Space group Fd 3 m (No. 227)Template: room group / 227
Lattice parameters a  = 10.575  Å
Formula units Z  = 8
Frequent crystal faces {111}, {100}
Physical Properties
Mohs hardness ≈ 6; VHN = 610 (40 g load) kg / mm²
Density (g / cm 3 ) 7.523 (measured); 7.122 (calculated)
Cleavage no
Break ; Tenacity uneven; brittle
colour yellowish brown
Line color White
transparency translucent
shine Greasy shine
radioactivity radioactive due to uranium content
Crystal optics
Refractive index n  = 1.95 to 2.02
Optical character isotropic

Keno plumbo microlite is a rare mineral from the mineral class of oxides and hydroxides . It crystallizes in the cubic crystal system with the composition (Pb, □) 2 Ta 2 O 6 [□, (OH), O]. It is therefore a lead - tantalate , the Y position of which is largely unoccupied, ie characterized by vacancies.

Kenoplumbo microlite occurs at its type locality in the form of idiomorphic , octahedral crystals of up to 20 cm in size, which very often contain inclusions of uraninite and mostly with albite of the variety cleavelandite , microcline , biotite , cassiterite , galena , hingganite (Yb) and others Uranium minerals are associated.

The type locality is the Kenoplumbomikroliths a 2.5 km west of the mountain Vyuntspakhk and about 80 km east of the village Lovozero lying Amazonit -Pegmatit on the Mountain "Ploskaja" ( coordinates of the mountain Ploskaja ) in the western "Keivy massif" on the Kola Peninsula in Murmansk Oblast , Russia ( Russian: Гора Плоская, Западные Кейвы, Кейвы, Кольский полуостров, Ловозерский район, Мурмаский район, Мурманя байон, Растьонскось ибяский ). This finding point is already type locality for Hingganit- (Yb) , Keiviit- (Y) , Keiviit- (Yb) , Kuliokit- (Y) and Vyuntspakhkit- (Y) .

Etymology and history

Alexandre Safiannikoff and Leopold van Wambeke (1961) first described a lead-rich microlite from an alluvial tin deposit in the Congo ("Mumba Cassiterite Gravels" near Mumba in the Masisi Mountains, North Kivu , Democratic Republic of the Congo ) and named it as, according to its chemical composition Plumobomicrolite (originally French plombomicrolite ). However, they had never formally introduced the name “plumobomicrolite” for this Pb-dominant member of the microlite pyrochlore family; this was only done in 1964 by Max Hutchinson Hey due to its meanwhile established use in literature. In the first "Classification and nomenclature of the pyrochlore group" in 1977 Donald David Hogarth kept the name "plumbomicrolite" to underline the fact that the mineral belongs to the microlith subgroup within the pyrochlore group.

After the first appearance of a "plumbomicrolite" in the quarry No. 1 was observed in the vein-shaped Amazonite pegmatite "Ploskaja" on the southwest slope of the Keivy Mountains on the Kola Peninsula, the mineral from this site has been described several times at the beginning of the 1980s.

In 2010, the IMA presented a new nomenclature for the minerals of the newly defined pyrochlore upper group (pyrochlore supergroup). From this it follows that the Pb-Ta- □ -dominant member of this upper group is to be referred to as keno plumbo microlite.

After a plumbomicrolite handed over to Roy Kristiansen by Victor Stepanov had already been structurally examined by Luca Bindi and colleagues, the chemical, physical and optical properties of this find point were examined at a further plumbomicrolite stage by an international team of scientists led by Daniel Atencio. The steps turned out to be identical to kenoplumbo microlite in the sense of the new nomenclature of the pyrochlore upper group. The new mineral was presented to the International Mineralogical Association (IMA), which recognized it in 2015 under the provisional designation IMA 2015-007a . The first scientific description of this mineral was made in 2018 by an international team of researchers with Daniel Atencio , Marcelo B. Andrade , Luca Bindi , Paola Bonazzi , Matteo Zoppi , Chris J. Stanley and Roy Kristiansen in the English science magazine Mineralogical Magazine . The authors named the mineral in accordance with the nomenclature of the pyrochlore upper group due to its chemical composition with an A position dominated by lead , a B position dominated by Ta and a Y position dominated by vacancies ( gaps ) as kenoplumbomicrolite ( English kenoplumbomicrolite ), where the suffix "Keno" - according to a suggestion by François Permingeat, goes back to the Greek word κενος [ kenos ] for "empty".

The type material for keno plumbo microlite is stored under catalog number DR980 (holotype) in the collection of the “Museu de Geociências” at the “Instituto de Geociências”, Universidade de São Paulo in São Paulo , state of São Paulo (federal state) , Brazil.

Microlite was originally found near Chesterfield in the US state of Massachusetts and was described in 1835 by Charles U. Shepard (1804-1886). Shepard named the mineral after the Greek words μικρός [ micros ] and λίθος [ lithos ] for "small" and "stone" because of its tiny, maximum ¼ inch crystals. Over the decades, the term microlite has often been used unspecifically and often without the background of chemical analysis. The mineral Mikrolith was discredited in 2010, but Mikrolith is the namesake for the Mikrolith subgroup within the Pyrochlore upper group.

classification

The current classification of the International Mineralogical Association (IMA) counts the kenoplumbomicrolite to the pyrochlore upper group with the general formula A 2– m B 2 X 6– w Y 1– n , in which A , B , X and Y different positions in the structure the minerals of the pyrochlore upper group with A  = Na, Ca, Sr, Pb 2+ , Sn 2+ , Sb 3+ , Y, U, □, or H 2 O; B = Ta 5+ , Nb 5+ , Ti 4+ , Sb 5+ , W 6+ , Al 3+, or Mg 2+ ; X = O, OH or F and Y = OH - , F, O, □, H 2 O or very large (>> 1.0 Å) monovalent cations such as K, Cs or Rb. To pyrochlore supergroup include not only Kenoplumbomikrolith still Fluorcalciomikrolith , Fluornatromikrolith , Hydrokenomikrolith , Hydroxycalciomikrolith , Hydroxykenomikrolith , Oxynatromikrolith , Oxystannomikrolith , Oxystibiomikrolith , Cesiokenopyrochlor , Fluorcalciopyrochlor , Fluornatropyrochlor , Hydrokenopyrochlor , Hydropyrochlor , Hydroxycalciopyrochlor , Hydroxykenopyrochlor , Hydroxymanganopyrochlor , Hydroxynatropyrochlor , Oxycalciopyrochlor , Fluorcalcioroméit , Hydroxycalcioroméit , Hydroxyferroroméit , Oxycalcioroméit , Oxyplumboroméite , Hydrokenoelsmoreit , Hydroxykenoelsmoreit , Fluornatrocoulsellit and Hydrokenoralstonit . Kenoplumbomicrolite, together with fluorocalciomicrolite, fluoronatromicrolite, hydrokenomicrolite, hydroxycalciomicrolite, hydroxykenomicrolite, oxynatromicrolite, oxystannomicrolite and oxystibiomicrolite, form the microlite group within the pyrochlore upper group .

The 8th edition of the mineral systematics according to Strunz , which is now outdated but still in use , does not yet list the oxyplumboroméite, but assigns the plumbomicrolite to the mineral class of "oxides and hydroxides" and there to the general section of "oxides with a metal: oxygen ratio = 2 : 3 (M 2 O 3 and related compounds) "where he together with Bariomikrolith (discredited 2010), possibly Hydrokenomikrolith, Bismutomikrolith (discredited 2010), Fluornatromikrolith , Mikrolith , Natrobistantit , Stannomikrolith (2010 redefined to Oxystannomikrolith) Stibiomikrolith (2010 to Oxystibiomikrolith redefined) and uranium microlite the "pyrochlore group, microlith subgroup" with the system no. IV / C.18 .

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), classifies the keno plumbo microlite in the category of "oxides with the molar ratio of metal: oxygen = 1: 2 and comparable". However, this section is further subdivided according to the relative size of the cations involved and the crystal structure, so that the mineral according to its composition and structure is classified in the sub-section “With large (± medium-sized) cations; Layers of edge-linked octahedra ”can be found, where together with all representatives of the pyrochlore, microlith, Betafit, Roméit and Elsmoreit groups, the pyrochlore supergroup with the system no. 4.DH.15 forms. Kenoplumbomikrolith is (formerly with Fluorcalciomikrolith, Fluornatromikrolith, Hydrokenomikrolith, Hydromikrolith, Hydroxykenomikrolith Cesstibtantit ) (formerly, Oxycalciomikrolith, Oxystannomikrolith Stannomikrolith ) (formerly and Oxystibiomikrolith Stibiomikrolith ) found in the Mikrolithgruppe.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the plumbomicrolite to the class of "oxides and hydroxides", but there in the category of "multiple oxides with Nb, Ta and Ti". Here it is together with microlite, bariomicrolite, fluorine atromicrolite, uranium microlite, bismuthomicrolite, stannomicrolite and stibiomicrolite in the "microlite subgroup; Ta> Nb; (Ta + Nb) > 2 (Ti) “with the system no. 02/08/02 within the subsection of " Multiple oxides with Nb, Ta and Ti with the formula A 2 (B 2 O 6 ) (O, OH, F) ".

Chemism

Four microprobe analyzes on a keno plumbo microlite grain from the type locality yielded mean values ​​of 0.37% Na 2 O; 2.51% CaO; 45.39% PbO; 1.24% UO 2 ; 28.58% Ta 2 O 5 ; 12.90% Nb 2 O 5 ; 0.84% ​​TiO 2 ; 2.19% SiO 2 ; 1.28% Fe 2 O 3 ; 0.07% Al 2 O 3 and 0.35% H 2 O (calculated); Sum = 99.19%. On the basis of two cations on the B position per formula unit, the empirical formula (Pb 1.30 □ 0.30 Ca 0.29 Na 0.08 U 0.03 ) Σ = 2.00 (Ta 0.82 Nb 0.62 Si 0.23 Sn 4+ 0.15 Ti 0.07 Fe 3+ 0.10 Al 0.01 ) Σ = 2.00 O 6 [□ 0.52 (OH) 0.25 O 0, 23 ] Σ = 1.00 calculated, which has been simplified to (Pb, □) 2 Ta 2 O 6 [□, (OH), O]. Increased uranium content can be traced back to the inclusions of idiomorphic uraninite crystals up to 10 µm in size already observed by Anatoly Voloshin and colleagues (1981).

Kenoplumbo microlite is the only mineral with the element combination Pb - Ta - O - H. Chemically similar are cesplumtantite , (Cs, Na) 2 (Pb, Sb 3+ ) 3 Ta 8 O 24 ; Rankamaite , (Na, K) 3 (Ta, Nb, Al) 11 (O, OH) 31 ; Zimbabweit , (Na, K) 2 PbAs 4 (Ta, Nb, Ti) 4 O 18 as well as hydroxyplumbopyrochlore not yet described as a mineral , (Pb, Ca) 2-x (Nb, Ti, Ta) 2 O 6 (OH) .

Within the pyrochlore upper group there are theoretically a multitude of substitution possibilities due to the four different positions to be occupied. Keno plumbo microlite has no analogues within the microlite group; there are also no cross-subgroup analogues known. In principle, plumbomicrolite is not identical to keno plumbo microlite. Minerals previously described as plumbomicrolite are zero-valent dominant microlite.

Crystal structure

Crystal structure of keno plumbomicrolite as a cation-centered polyhedral representation

Kenoplumbo microlite crystallizes in the cubic crystal system in the space group Fd 3 m (space group no. 227) with the lattice parameter a = 10.575  Å and eight formula units per unit cell . Template: room group / 227

In the crystal structure of the kenoplumbomicrolite, assuming a "normal" pyrochlore structure, the A cation is on the 16 d position, the B cation is on the 16 c position, X is on the 48 f - and Y is on the 8 b - Position localized. Pb 2+ is fully ordered on the A position. Since the Y position is only partially occupied, the Pb 2+ ion can be locally coordinated six, seven or eight times. If two neighboring Y positions are empty (vacant), six X atoms around the A position form a trigonally distorted octahedron . In contrast, a trigonal scalenohedron is formed when two Y positions around the A positions are occupied. If only one of the neighboring Y positions is occupied, the A cation adopts an asymmetric seven-fold pyramidal coordination. The latter coordination is strongly preferred because of the stereoactive lone pair of electrons of Pb 2+ .

Kenoplumbo microlite is isotypic (isostructural) to all other representatives of the pyrochlore upper group which crystallize in space group Fd 3 m (space group no. 227) . Template: room group / 227

properties

morphology

Plumbo microlite was first found in 1975 in Quarry No. 1 of the amazonite pegmatite "Ploskaja" is known in the form of irregularly shaped single crystalline masses of up to 15 × 15 × 12 cm in size, which occur in the pegmatite at the contact between biotite and microcline and have poorly developed crystal surfaces. The surfaces of the octahedron {111} and the hexahedron {100} are formed at the contact with the biotite . In 1976, more plumbomicrolites were extracted from quarry No. 5 of the same pegmatite dike. They form octahedral crystals up to 3 cm in size on the albite variety Cleavelandite. Octahedral and cuboctahedral keno plumbomicrolite crystals up to 20 cm in size are known. In the keno plumbo microlite crystals, radial cracks originating from uraninite crystals appear, which are interpreted as the result of micro-cracking caused by radioactivity. Uraninite is subject to intense self-irradiation, which can lead to amorphization ( metamictization ), whereby the volume of the mineral increases, which causes the formation of cracks in the surrounding mineral.

physical and chemical properties

The crystals of the keno plumbomicrolite are yellowish brown, while the plumbomicrolite is yellow to orange, green to yellowish green or dark brown to black. The line color of the keno plumbo microlith is indicated as white. The surfaces of the translucent keno plumbo microlite show a greasy sheen . The high gloss agrees very well with the high value for light refraction (n = 1.95 to 2.02). When viewed in incident light, kenoplumbo microlite shows no internal reflections and is optically completely isotropic.

Kenoplumbo microlite has no cleavage , but because of its brittleness it breaks like amblygonite , with the fracture surfaces being uneven. With a Mohs hardness of ≈ 6, the mineral is one of the medium-hard minerals and, like the reference mineral orthoclase (hardness 6), can only be scratched with a steel file. The Vickers hardness for plumbomicrolite was determined to be VHN 40  = 610-670 kg / mm². The measured density for keno plumbo microlite is 7.523 g / cm³; the calculated density 7.122 g / cm³. The differences between the calculated and measured density are due on the one hand to changing contents of Ta or Nb and on the other hand to uraninite inclusions.

Kenoplumbomikrolith is neither in the long wavelength even in the short wavelength UV light , a fluorescent .

Education and Locations

The type locality for Kenoplumbomikrolith is a 2.5 km west of the mountain Vyuntspakhk and about 80 km east of the village Lovozero lying Amazonit -Pegmatit on the Mountain "Ploskaja" western "Keivy massif" on the Kola Peninsula in the Murmansk Oblast, Russia. The vein-shaped pegmatites discovered in 1955 and investigated since 1956 also include the 220 m long and 8 to 25 m thick pegmatite vein No. 19, also called Ploskogorskoe, which consists of quartz, quartz-amazonite-albite and amazonite zones and is now considered the world's largest amazonite deposit . The thickness of the zones with blocky amazonite reaches up to 8 m. The quartz core in the center of the pegmatite contains drusen with a diameter of up to 40 cm with galena and coarse-grained biotite scales as well as cleavelandite.

As Begleitminerale of Kenoplumbomikroliths be microcline (Var. Amazonit ), albite (Var. Cleavelandit ), quartz , biotite , zinnwaldite , Anglesit , Bastnäsit- (Ce) , bismite , bismuth , Bismuthinit , Bismutit , Caysichit- (Y) , Churchit- ( Y) , columbite (Mn) , emplektite , fergusonite (Y) , fluorite , gadolinite (Y) , gahnite , galena , hingganite (Y) , hingganite (Yb) , kainosite (Y) , kamphaugite ( Y) , cassiterite , Kasolite , Keiviit- (Y) , Keiviit- (Yb) , Kuliokit- (Y) , Lanarkit , Leadhillit , Löllingit , further representatives of the pyrochlore upper group Monazit- (Ce) , Pyromorphit , Scotlandit , sillenite , sphalerite , Tengerit- (Y) , Thalénit- (Y) , thorite , uraninite , Vyuntspakhkit- (Y) , Wulfenit , xenotime (Y) , xenotime (Yb) and Zavaritskit mentioned.

As a very rare mineral formation, the keno plumbo microlite could so far (as of 2018) only be described by its type locality. Plumbo microlite is known from around 15 sites worldwide. In addition to the mountain "Ploskaja", these include:

Locations for kenoplumbo microlite in Germany , Austria and Switzerland are therefore unknown.

use

Due to its rarity, kenoplumbo microlite is of no practical importance and only of interest to mineral collectors.

See also

literature

  • Daniel Atencio, Marcelo B. Andrade, Luca Bindi, Paola Bonazzi, Matteo Zoppi, Chris J. Stanley, Roy Kristiansen: Kenoplumbomicrolite, (Pb, □) 2 Ta 2 O 6 [ □, (OH), O], a new mineral from Ploskaya, Kola Peninsula, Russia . In: Mineralogical Magazine . tape 82 , no. 5 , 2018, p. 1049-1055 , doi : 10.1180 / minmag.2017.081.082 (English).
  • Plumbomicrolite . 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; 72 kB ; accessed on October 24, 2018]).

Web links

Commons : Kenoplumbomicrolite  - collection of pictures, videos and audio files

Individual evidence

  1. ↑ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad Daniel Atencio, Marcelo B. Andrade, Luca Bindi, Paola Bonazzi, Matteo Zoppi, Chris J Stanley, Roy Kristiansen: Kenoplumbomicrolite, (Pb, □) 2 Ta 2 O 6 [ □, (OH), O], a new mineral from Ploskaya, Kola Peninsula, Russia . In: Mineralogical Magazine . tape 82 , no. 5 , 2018, p. 1049-1055 , doi : 10.1180 / minmag.2017.081.082 (English).
  2. ↑ a b c d Anatoly Vasil'evich Voloshin, Vladimir V. Bukanov, Lyudmila Ivanovna Polezhaeva: Plumbomicrolite and plumbopyrochlore from amazonite pegmatites of the Kola Peninsula . In: Mineralogicheskij zhurnal . tape 3 , 1981, p. 20–34 (Russian).
  3. ↑ a b - Plumbomicrolite , (accessed October 24, 2018) (English)
  4. ↑ a b Alexandre Safiannikoff, Leopold van Wambeke: Sur un terme plombifère du groupe pyrochlore-microlite . In: Bulletin de la Société Francaise de Minéralogie et de Cristallographie . tape 84 , 1961, pp. 382–384 (French, rruff.info [PDF; 214 kB ; accessed on October 24, 2018]).
  5. ^ Max Hutchinson Hey: Twenty-third list of new mineral names . In: Mineralogical Magazine . tape 33 , 1964, pp. 1125–1158 (English, minersoc.org [PDF; 1.8 MB ; accessed on October 24, 2018]).
  6. ^ Donald David Hogarth: Classification and nomenclature of the pyrochlore group . In: The American Mineralogist . tape 62 , 1977, pp. 403-410 (English, rruff.info [PDF; 849 kB ; accessed on September 3, 2018]).
  7. ↑ Victor Ivanovich Stepanov, Vladimir V. Bukanov, Alexandra Vasilyevna Bykova (В.И. Степанов, В.В. Буканов, А.В. Быкова): Plumbomicrolite from amazonite pegmatite of Ploskaya Mountain - first place in USSR ( Плюмбомикролит из амазонитового пегматита горы Плоской - первая находка в СССР) . In: Doklady Akademii Nauk SSSR ( Докл. Акад. Наук СССР) . tape 263 , no. 1 , 1982, pp. 183-185 (Russian).
  8. ↑ a b c d e f g h Daniel Atencio, Marcelo B. Andrade, Andrew G. Christy, Reto Gieré, Pavel M. Kartashov: The Pyrochlore supergroup of minerals: Nomenclature . In: The Canadian Mineralogist . tape 48 , 2010, p. 673–698 , doi : 10.3749 / canmin.48.3.673 (English, rruff.info [PDF; 1,4 MB ; accessed on August 30, 2018]).
  9. ↑ a b c Luca Bindi, Matteo Zoppi, Paola Bonazzi: Plumbomicrolite from the Ploskaya Mountain, Keivy Massif, Kola Peninsula, Russia: composition and crystal structure . In: Periodico di Mineralogia . tape 75 , no. 2 , 2006, p. 51–58 (English, researchgate.net [PDF; 202 kB ; accessed on October 24, 2018]).
  10. ^ A b Charles Upham Shepard : Microlite, a new mineral species . In: The American Journal of Science and Arts . tape  27 , no. 2 , 1835, p. 361–362 , doi : 10.1184 / pmc / AJS / AJS_1835_027_1835 (English, limited preview in Google Book Search).
  11. ^ Andrew G. Christy, Daniel Atencio: Clarification of the status of species in the pyrochlore supergroup . In: Mineralogical Magazine . tape 77 , no. 1 , 2013, p. 13–20 , doi : 10.1180 / minmag.2013.077.1.02 (English, main.jp [PDF; 85 kB ; accessed on August 30, 2018]).
  12. ↑ a b Mindat - Kenoplumbomicrolite , (accessed October 24, 2018) (English)
  13. ↑ Hartmut Beurlen, Dwight R. Soares, Rainer Thomas, Lucila E. Prado-Borges, Cláudia de Castro: Mineral chemistry of tantalate species new in the Borborema Pegmatitic Province, Northeast Brazil . In: Anais da Academia Brasileira de Ciências (Annals of the Brazilian Academy of Sciences) . tape 77 , no. 1 , 2005, p. 169–182 , doi : 10.1590 / S0001-37652005000100013 (English, scielo.br [PDF; 476 kB ; accessed on September 3, 2018]).
  14. ↑ Pavel Uher, Petr Černý, Ron Chapman: Foordite-thoreaulite, Sn 2+ Nb 2 O 6 –Sn 2+ Ta 2 O 6 : compositional variations and alteration products . In: European Journal of Mineralogy . tape 20 , no. 4 , 2008, p. 501-516 , doi : 10.1127 / 0935-1221 / 2008 / 0020-1845 (English).
  15. ^ Daniel Groult, Claude Michel, Bernard Raveau: Sur de nouveaux pyrochlores lacunaires d'ions bivalents synthetises par echanges d'ions . In: Journal of Inorganic and Nuclear Chemistry . tape 37 , 1975, pp. 2203-2205 , doi : 10.1016 / 0022-1902 (75) 80857-8 (French).
  16. ↑ a b c plumbomicrolite . 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; 72  kB ; accessed on October 24, 2018]).
  17. ↑ Mindat - Mountain "Ploskaja" locality in the western "Keivy Massif" on the Kola Peninsula in Murmansk Oblast, Russia , (accessed October 24, 2018) (English)
  18. ↑ a b Mindat - Number of localities for Keno plumbo microlite , (accessed October 24, 2018) (English)
  19. ↑ a b List of localities for kenoplumbomicrolite in the Mineralienatlas and Mindat (accessed October 24, 2018)