Fluorine atomic microlite
| Fluorine atomic microlite | |
|---|---|
 |
|
| General and classification | |
| other names |
IMA 1998-018 |
| chemical formula | (Na, Ca, Bi) 2 Ta 2 O 6 F |
|
Mineral class (and possibly department) |
Oxides and hydroxides |
|
System no. to Strunz and to Dana |
4.DH.15 ( 8th edition : IV / C.18) 02/08/02/08 |
| Crystallographic Data | |
| Crystal system | cubic |
| Crystal class ; symbol | cubic hexakisoctahedral; 4 / m 3 2 / m |
| Space group | Fd 3 m (No. 227) |
| Lattice parameters | a = 10.4451 Å |
| Formula units | Z = 8 |
| Physical Properties | |
| Mohs hardness | 5 |
| Density (g / cm 3 ) | 6.49 (measured); 6.568 (calculated) |
| Cleavage | not observed |
| Break ; Tenacity | clamshell; brittle |
| colour | green, orange-yellow |
| Line color | White |
| transparency | transparent |
| shine | Diamond luster |
| Crystal optics | |
| Refractive index | n = 2.110 |
| Optical character | isotropic |
Fluorine atomic microlite is a very rare mineral from the mineral class of " oxides and hydroxides ". It crystallizes in the cubic crystal system with the idealized chemical composition (Na, Ca, Bi) 2 Ta 2 O 6 F. The elements sodium , calcium and bismuth indicated in the round brackets can represent each other in the formula ( substitution , diadochia), However, they are always in the same proportion to the other components of the mineral.
Fluorine atom crolite develops only small, isometric to flattened octahedral crystals of predominantly green color and a diamond-like sheen . In the meantime, however, orange to yellow color varieties have also been discovered.
Etymology and history
Was first discovered in 1998 in Fluornatromikrolith granite - pegmatite near Quixaba (administrative region free Martinho ) in the Brazilian state of Paraíba . It was analyzed and described by Thomas Witzke , Manfred Steins , Thomas Doering , Walter Schuckmann , Reinhard Wegner and Herbert Pöllmann and the mineral was recognized by the International Mineralogical Association (IMA) in the same year . Publication of the test results and recognition was delayed by several years, however, because the discovery of fluorine atomic microlite sparked a major debate about the mineral classification and nomenclature in the pyrochlore supergroup, as the recognized name did not fit into the nomenclature of this group that had been in use until then. After clarifying and redefining the nomenclature in 2010 by Atencio et al. the fluorine atomic microlite now counts as a member of the microlite group with dominant fluorine on the anion side. The mineral description including a new assignment took place in the following year.
Type material of the mineral was deposited in the Mineralogical Collection of the Technical University Bergakademie Freiberg (Reg.-No. 77975) and in the Mineralogical Collection of the Martin Luther University Halle-Wittenberg (Institute for Geological Sciences, No. 010356).
classification
The current classification of the International Mineralogical Association (IMA) counts the fluorine atromicrolite 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, Nb, Ti, Sb 5+ or W; 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 Fluornatromikrolith still Fluorcalciomikrolith , Hydrokenomikrolith , Hydroxycalciomikrolith , Hydroxykenomikrolith , Kenoplumbomikrolith , Oxynatromikrolith , Oxystannomikrolith , Oxystibiomikrolith , Cesiokenopyrochlor , Fluorcalciopyrochlor , Fluornatropyrochlor , Hydrokenopyrochlor , Hydropyrochlor , Hydroxycalciopyrochlor , Hydroxykenopyrochlor , Hydroxymanganopyrochlor , Hydroxynatropyrochlor , Oxycalciopyrochlor , Fluorcalcioroméit , Hydroxycalcioroméit , Hydroxyferroroméit , Oxycalcioroméit , Oxyplumboroméite , Hydrokenoelsmoreit , Hydroxykenoelsmoreit , Fluornatrocoulsellit and Hydrokenoralstonit . Fluorine atomic microlite, together with fluorocalciomicrolite, hydrokenomicrolite, hydroxycalciomicrolite, hydroxykenomicrolite, kenoplumbomicrolite, oxynatromicrolite, oxystannomicrolite and oxystibiomicrolite, form the microlite group within the pyrochlore upper group .
In the meanwhile outdated, but still in use 8th edition of the mineral systematics according to Strunz , the fluorine atromicrolite belonged to the general section of "Oxides with a metal: oxygen ratio = 2: 3 (M 2 O 3 and related compounds)", where together with bariomicrolite , Bismutomikrolith , Mikrolith , Natrobistantit , Plumbomikrolith , Stannomikrolith , Stibiomikrolith and Uranmikrolith the " Pyrochlorgruppe , Mikrolith 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 fluorine atomic 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 it forms together with / as the only member the unnamed group 4.DH.15 .
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the fluorine atomic microlite 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, plumbomicrolite, 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
Seventeen microprobe analyzes on fluorine atomic microlite from the granite pegmatite "Alto Quixaba" resulted in mean values of 6.39% Na 2 O; 6.96% CaO; 6.71% Bi 2 O 3 ; 76.81% Ta 2 O 5 and 3.63% F and [(O ≡ F) -1.53%, sum = 98.97%]. On the basis of two Ta cations on the B position, the empirical formula (Na 1.10 Ca 0.64 Bi 0.15 ) Ta 2.00 O 5.91 F 1.02 was determined, which leads to (Na, Ca, Bi) 2 Ta 2 O 6 F has been simplified. Within the pyrochlore upper group there are theoretically a multitude of substitution possibilities due to the four different positions to be occupied. Fluorine atomic microlite is the Na-dominant analogue of the Ca-dominated fluorocalciomicrolite and the F-dominant analogue of the O-dominated oxynatromicrolite
The mineral fersmit , (Ca, Ce, Na) (Nb, Ta, Ti) 2 (O, OH, F) 6 is also chemically similar .
Crystal structure
Fluorine atomic microlite crystallizes cubically in the space group Fd 3 m (space group no. 227) with the lattice parameter a = 10.4451 (2) Å and eight formula units per unit cell .
As with all representatives of the pyrochlore upper group, the crystal structure of the fluorine atomic microlite consists of - in this case - TaO 6 - octahedra with common corners, which form parallel layers of three and six rings [110]. Tantalum is coordinated by six equivalent oxygen atoms that form an almost ideal octahedron. In the layers mentioned there are channels in the direction 110, which take up the oxygen atoms and the atoms in the A position such as Na, Ca and Bi. Again, these atoms form (Na, Ca, Bi) O 6 F 2 - polyhedron , which are joined together by common edges.
properties
morphology
At its type locality, fluorine atomic microlite was found in idiomorphic or plate-like distorted crystals up to 6 mm in size.
physical and chemical properties
The crystals of fluorine atomic microlite are green (type locality) or orange-yellow (pegmatite field Dara-i-Pech), their line color , however, is always white. The surfaces of the fluorine atomic microlite, which is transparent in thin fragments, show a diamond-like sheen , which agrees well with the very high value for the refraction of light (n = 2.110).
Fluorine atomic microlite shows no cleavage . Due to its brittleness , however , it breaks in a similar way to quartz , with the fracture surfaces being shell-shaped. With a Mohs hardness of 5, the mineral is one of the medium-hard minerals and, like the reference mineral apatite, can still be scratched with a pocket knife. The measured density for fluorine atomic microlite was found to be 6.49 g / cm³, the calculated density is 6.568 g / cm³.
There is no information on fluorescence in UV light or on cathodoluminescence under the electron beam for the mineral.
Education and Locations
Fluorine atomic microlite is found in granitic pegmatites, with perthitic microcline , quartz and muscovite as the main mineral constituents at its type locality Quixabá . The accompanying minerals were mainly blue elbaite , tantalite (Fe) , tantalite (Mn) and green beryl .
As a very rare mineral formation, fluorine atomic microlite has so far only been proven in small quantities and at a few locations. So far (as of 2012) around 10 sites are known to be known. In Brazil, however, the mineral has so far only been found at its type locality.
Other sites include the Dara-i-Pech pegmatites and the "Paprok Mine" near Kamdesh in Afghanistan , the pegmatites from Viitaniemi near Eräjärvi / Orivesi in Finland , the "Mokrusha Mine" near Yuzhakovo in the Russian Oblast of Sverdlovsk (Ural) , Forcioni, Sant'Ilario in Campo, Campo nell'Elba island of Elba in the Tuscan archipelago , Livorno , region Tuscany in Italy , the lithium - rubidium - cesium -Pegmatit of Nová Ves u Brloha , Český Krumlov District , South Bohemia , Czech Republic , the "Naipa Mine" near Alto Ligonha in Mozambique , the Shigartal in Pakistan , as well as a quarry near Bennett in Oxford County (Maine) and the "Cryo-Genie Mine" near Warner Springs in the Warner Springs District, San Diego County , California , both in the US .
use
Due to its rarity, fluorine atomic microlite is a sought-after mineral by mineral collectors, but otherwise of no practical importance.
See also
literature
- Thomas Witzke , Manfred Steins, Thomas Doering, Walter Schuckmann, Reinhard Wegner, Herbert Pöllmann: Fluornatromicrolite, (Na, Ca, Bi) 2 Ta 2 O 6 F, a new mineral species from Quixaba, Paraíba, Brazil , In: The Canadian Mineralogist , Volume 49 (2011), pp. 1105-1110 doi : 10.3749 / canmin.49.4.1105
Web links
- Mineral Atlas: Fluorine Atomic Microlite (Wiki)
- Mindat - fluorine atomicrolite
- Web mineral - fluorine atomicrolite
Individual evidence
- ↑ a b c d e f g h i j k l m n o p q r Thomas Witzke et al .: Fluornatromicrolite (see literature)
- ^ A b 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]).
- ↑ Marcelo B. Andrade, Daniel Atencio, Aba IC Persiano and Javier Ellena (2013): Fluorcalciomicrolite, (Ca, Na, □) 2 Ta 2 O 6 F, a new microlite-group mineral from Volta Grande pegmatite, Nazareno, Minas Gerais , Brazil. In: Mineralogical Magazine , Volume 77, pp. 2989-2996.
- ↑ Fan Guang, Ge Xiangkun, Li Guowu, Yu Apeng and Shen Ganfu: Oxynatromicrolite, (Na, Ca, U) 2 Ta 2 O 6 (O, F), a new member of the pyrochlore supergroup from Guanpo, Henan Province, China . In: Mineralogical Magazine . tape 81 , no. 4 , 2017, p. 743–751 , doi : 10.1180 / minmag.2016.080.121 (English).
- ↑ a b Mindat - fluorine atomicrolite
- ^ A b 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. 222-223 .
- ↑ Mindat - Number of localities for fluorine atomic microlite