Fluorapophyllite (Cs)

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Fluorapophyllite (Cs)
General and classification
other names

IMA 2018-108a

chemical formula
  • CsCa 4 (Si 8 O 20 ) F (H 2 O) 8
  • CsCa 4 [F | (Si 4 O 10 ) 2 ] • 8H 2 O
Mineral class
(and possibly department) 		Silicates and germanates ( phyllosilicates )
Crystallographic Data
Crystal system tetragonal
Crystal class ; symbol ditetragonal-dipyramidal; 4 / m  2 / m  2 / m
Space group P 4 / mnc (No. 128)Template: room group / 128
Lattice parameters a  = 9.060  Å ; c  = 15.741 Å
Formula units Z  = 2
Physical Properties
Mohs hardness 4.5 to 5; Vickers hardness VHN 100  = 480 kg / mm 2
Density (g / cm 3 ) 2.54 (measured); 2.513 (calculated)
Cleavage very perfect
Break ; Tenacity brittle; stepped
colour colorless
Line color White
transparency probably transparent
shine Glass gloss
Crystal optics
Refractive indices n ω  = 1.540
n ε  = 1.544
Birefringence δ = 0.004
Optical character uniaxial positive
Pleochroism none

Fluorapophyllite (Cs) is a very rare mineral from the group of apophyllites within the mineral class of "silicates and germanates" with the chemical composition CsCa 4 (Si 8 O 20 ) F (H 2 O) 8 and is therefore chemically one water - containing cesium - calcium - silicate with additional fluoride - ions. Structurally it belongs to the layered silicates .

The mineral crystallizes in the tetragonal crystal system and forms separate grains up to 0.08 mm in diameter in quartz - pectolite - mineral aggregates as well as zones in up to 0.2 mm large fluorapophyllite (K) grains. The separate fluoroapophyllite (Cs) grains have an irregular shape.

Its type locality is the moraine of the Darai-Pioz glacier ( coordinates of the Darai-Pioz glacier ) in Alay Mountains , Tian Shan , Districts of Republican Subordination ( "imputed the Republic of territories", more or less identical to the historical region Karotegin) Northern Tajikistan .

Etymology and history

The multi-phase Darai-Pioz rock massif is type locality for currently (2020) 40 different minerals recognized by the IMA, including a number of cesium-containing phases. The first of these minerals was the Kupletkit- (Cs), first described in 1971 . In 2017 alone, four further minerals containing cesium were first described from the moraine of the Darai-Pioz glacier: Odigitriaite , CsNa 5 Ca 5 [Si 14 B 2 O 38 ] F 2 (IMA 2015-028); Mendeleevit- (Nd) , (Cs, ☐) 6 (☐, Cs) 6 (☐, K) 6 (REE, Ca) 30 (Si 70 O 175 ) (OH, H 2 O, F) 35 (IMA 2015- 031); Garmit , CsLiMg 2 (Si 4 O 10 ) F 2 (IMA 2017-008); and Gorbunovit , CsLi 2 (Ti, Fe) (Si 4 O 10 ) (F, OH, O) 2 (IMA 2017-040). In this context, an international working group led by the mineralogist Atali A. Agakhanov examined fluorapophyllites from the Darai-Pioz rock massif . After corresponding analyzes it turned out that on the one hand fluorapophyllite (K) crystals with cesium-rich zones exist from this locality and that on the other hand, even Cs-dominant "fluorapophyllites" occur in quartz-pectolite aggregates from this locality. This phase turned out to be a new representative of the apophyllite group .

The new mineral was presented to the International Mineralogical Association (IMA), which recognized it in 2018 under the provisional designation "IMA 2018-108a". The first scientific description of this mineral took place in 2019 by an international research team with Atali A. Agakhanov, Leonid A. Pautov, Anatoly V. Kasatkin, Vladimir Yu. Karpenko, Elena Sokolova, Maxwell C. Day, Frank C. Hawthorne, Vyacheslav A. Muftakhov, Igor V. Pekov, Fernando Cámara, Sergey N. Britvin in the international science magazine The Canadian Mineralogist . The authors named the new representative of the apophyllite group in accordance with the nomenclature of this mineral group and due to its chemical composition with cesium on the A position and F> OH as fluorapophyllite (Cs) ( English fluorapophyllite (Cs) ).

The type material ( holotype ) for fluorapophyllite (Cs) is kept under catalog number 5280/1 in the systematic collection of the Mineralogical Museum " Alexander Evgenjewitsch Fersman " of the Russian Academy of Sciences in Moscow .

classification

The 8th edition of the mineral classification according to Strunz , which is now outdated, but still in use in some cases, does not yet list the fluorapophyllite (Cs). It would belong to the mineral class of "silicates and germanates" and there to the general division of "phyllosilicates", where together with fluorapophyllite (K) , hydroxyapophyllite (K) and fluorapophyllite (Na) the "apophyllite series “With the system no. VIII / E.01b within the "Gillespit-Apophyllite Group" and the subdivision "With tetragonal or pseudotetragonal layer structures".

The 9th edition of Strunz's mineral systematics, which has been in effect since 2001 and was updated by the International Mineralogical Association (IMA) until 2009, also does not yet know the fluorapophyllite (Cs). It is expected to be assigned to the class of "silicates and germanates" and there in the department of "phyllosilicates". This section is, however, further subdivided according to the structure of the layers, so that the mineral, according to its structure, would be found in the sub-section “Simple tetrahedral networks with 4, 5, (6) and 8 participating rings”, where it can be found together with fluorapophyllite (K ), Hydroxyapophyllite (K) and fluorapophyllite (Na) the apophyllite group with system no. 9.EA.15 will form.

The systematics of minerals according to Dana , which is mainly used in the English-speaking area , does not yet know the fluorapophyllite (Cs). Presumably it will be assigned to the class of "silicates and germanates" and there in the department of "layered silicate minerals". Here it would be together with fluorapophyllite (K), hydroxyapophyllite (K), fluorapophyllite (Na) and carletonite in the " apophyllite group (4- and 8-membered rings) " with system no. 72.03.01 within the sub-section " Layered silicates: two-dimensional, unlimited layers with rings other than six-membered: 3-, 4-, or 5-membered rings and 8-membered rings ".

Chemism

Average values from ten microprobe analyzes on a fluorapophyllite (Cs) grain of the type locality yielded 48.78% SiO 2 ; 0.05% Al 2 O 3 ; 22.69% CaO; 10.71 Cs 2 O; 1.13% K 2 O; 0.04% Na 2 O; 14.61% H 2 O (calculated from the crystal structure analysis) and 1.86% F [(O ≡ F) -0.78%, sum = 99.09%]. On the basis of 29 (O + F) atoms per formula unit (apfu) (H 2 O = 8 per formula unit was calculated from the crystal structure), the empirical formula (Cs 0.75 K 0.24 ) Σ = 0 is calculated from this .99 (Ca 3.99 Na 0.01 ) Σ = 4.0 (Si 8.01 Al 0.01 ) Σ = 8.02 O 20.03 F 0.97 (H 2 O) 8 , which leads to ( Cs, K) (Ca, Na) 4 (Si, Al) 8 O 20 F (H 2 O) 8 can be simplified and idealized to CsCa 4 Si 8 O 20 F (H 2 O) 8 . This idealized formula requires 48.03% SiO 2 ; 22.41% CaO; 14.07% Cs 2 O; 14.40% H 2 O and 1.90% F [(O ≡ F 2 ) -0.80%, sum = 100.00%].

The official formula of the IMA for the fluorapophyllite (Cs) corresponds to the spelling of Agakhanov and colleagues and is given as CsCa 4 (Si 8 O 20 ) F (H 2 O) 8 . The formula notation according to Strunz would, if one follows the notation for the other representatives of the apophyllite group, CsCa 4 [F | (Si 4 O 10 ) 2 ] · 8H 2 O read. As usual, the anion association is summarized here in square brackets.

The only combination of elements Cs – Ca – Si – O – H – F, as can be found in the official IMA formula for fluorapophyllite (Cs), only has fluorapophyllite (Cs) among the currently known minerals (as of 2020) . Chemically similar are mendeleevite- (Ce) , Cs 6 (Ce 22 Ca 6 ) (Si 70 O 175 ) (OH, F) 14 (H 2 O) 21 ; Mendeleevit- (Nd) , Cs 6 [(Nd, SEE) 23 Ca 7 ] (Si 70 O 175 ) (OH, F) 19 (H 2 O) 16 ; and potassium mendeleevite- (Ce) , Cs 6 K 6 (SEE 22 Ca 6 ) (Si 70 O 175 ) (OH, F) 20 (H 2 O) 15 .

From a chemical point of view, fluorapophyllite- (Cs) is the Cs-dominant analogue of K-dominated fluorapophyllite- (K) and Na-dominated fluorapophyllite- (Na). Fluorapophyllite- (Cs) and fluorapophyllite- (K) very likely form one complete mixed crystal row .

Crystal structure

Fluorapophyllite (Cs) crystallizes in the tetragonal crystal system in the space group P 4 / mnc (space group no. 128) with the lattice parameters a = 9.060  Å and c = 15.741 Å and two formula units per unit cell . Template: room group / 128

In the crystal structure of the Fluorapophyllit- (Cs) exists a T position that is occupied solely by Si, where Si is tetrahedrally coordinated by four oxygen atoms (SiO 4 - tetrahedron ). The SiO 4 tetrahedra are connected to one another and form a (Si 8 O 20 ) 8− layer perpendicular to [001]. In one layer, the SiO 4 tetrahedra are linked to form rings of 4 and 8. There are two cation positions A and B between the Si-O layers . The A position, which is mainly occupied by cesium, is coordinated by eight H 2 O groups [O (4) position]. The calcium-dominated [7] B position ideally contains four Ca atoms per formula unit and is coordinated by four oxygen atoms, two H 2 O groups and one fluorine atom. The Si-O layers are via A - and B - polyhedron and hydrogen bond linked. The geometry of the hydrogen bond corresponds to that in fluorapophyllite (K).

Fluorapophyllite- (Cs) is isotypic (isostructural) to fluorapophyllite- (K).

properties

morphology

Fluorapophyllite (Cs) is found in quartzolite boulders (extremely quartz-rich magmatites at the quartz tip of the line iron diagram ), where separate grains of up to 0.08 mm in diameter and zones up to 0, are found in quartz-pectolite-mineral aggregates Forms 2 mm fluorapophyllite (K) grains. The separate fluoroapophyllite (Cs) grains are xenomorphic , so they do not have a regular shape.

physical and chemical properties

The fluoroapophyllite (Cs) crystals are colorless, while their streak color is always white. The surfaces of the grains and aggregates, which are probably transparent according to the color of the mineral, show a characteristic glass-like sheen . Fluorapophyllite (Cs) has a medium-high refraction ( n ε  = 1.544; n ω  = 1.540) and a very low birefringence (δ = 0.004) corresponding to this glass gloss . In transmitted light, the uniaxial positive fluorapophyllite (Cs) is colorless and shows no pleochroism .

Fluorapophyllite (Cs) has a very perfect cleavage . Due to its brittleness , however , the mineral breaks in a similar way to halite or galena , with the broken surfaces being stepped. Fluorapophyllite (Cs) has a Mohs hardness of 4.5 to 5 and is therefore one of the medium-hard minerals that, with a corresponding crystal size, like the reference minerals fluorite (hardness 4) or fluorapatite (hardness 5) with a pocket knife (hardness 4) or less (hardness 5) can be slightly scratched. The Vickers hardness is VHN 100  = 480 kg / mm 2 , with values ​​between 468 and 502 kg / mm 2 being measured. The measured density for fluoroapophyllite (Cs) is 2.54 g / cm³, the calculated density is 2.513 g / cm³.

Fluorapophyllit- (Cs) is not in the long wavelength even in the short wave UV light , a fluorescent .

Education and Locations

Fluorapophyllite- (Cs) represents a hydrothermal formation at its type locality . It was formed in quartz-pectolite-mineral aggregates in extremely quartz-rich igneous rocks (quartzolite) in a multiphase intrusive complex. This is an alkali rock massif with boron-rich granitoids , which were placed in slates and which are criss-crossed by duct-shaped metasomatites and pegmatites .

Minerals accompanying fluorapophyllite (Cs) at its type locality are quartz, pectolite, baratovite , aegirine , leukosphenite , pyrochlore , neptunite , fluorapophyllite (K) and reed mergnerite .

As an extremely rare mineral formation, fluorapophyllite (Cs) (as of 2020) is only known from its type locality. The type locality of the fluorapophyllite (Cs) is the moraine of the "Darai-Pioz glacier" (also "Dara-i-Pioz glacier") in the Alai Mountains , Tian Shan , Nohijahoi tobei dschumhurij ("areas subject to the republic"; more or less identical to the historic Karotegin region), northern Tajikistan .

Locations from Germany , Austria and Switzerland are therefore unknown.

use

Due to its Cs 2 O content of a maximum of 14.07%, fluorapophyllite (Cs) would be an interesting cesium ore. But because of its rarity it is completely insignificant from an economic point of view.

See also

literature

  • Atali A. Agakhanov, Leonid A. Pautov, Anatoly V. Kasatkin, Vladimir Yu. Karpenko, Elena Sokolova, Maxwell C. Day, Frank C. Hawthorne, Vyacheslav A. Muftakhov, Igor V. Pekov, Fernando Cámara, Sergey N. Britvin: Fluorapophyllite- (Cs), CsCa 4 (Si 8 O 20 ) F (H 2 O) 8 , a new apophyllite-group mineral from the Darai-Pioz Massif, Tien-Shan, northern Tajikistan . In: The Canadian Mineralogist . tape 57 , no. 6 , 2019, pp. 965–971 , doi : 10.3749 / canmin.1900038 (English).

Web links

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 ae af ag ah ai aj ak al am an ao ap aq ar as at Atali A. Agakhanov, Leonid A. Pautov, Anatoly V. Kasatkin, Vladimir Yu. Karpenko, Elena Sokolova, Maxwell C. Day, Frank C. Hawthorne, Vyacheslav A. Muftakhov, Igor V. Pekov, Fernando Cámara, Sergey N. Britvin: Fluorapophyllite- (Cs), CsCa 4 (Si 8 O 20 ) F (H 2 O) 8 , a new apophyllite-group mineral from the Darai-Pioz Massif, Tien-Shan, northern Tajikistan . In: The Canadian Mineralogist . tape 57 , no. 6 , 2019, pp. 965–971 , doi : 10.3749 / canmin.1900038 (English).
  2. ↑ Frédéric Hatert, Stuart J. Mills, Marco Pasero, Peter A. Williams: CNMNC guidelines for the use of suffixes and prefixes in mineral nomenclature, and for the preservation of historical names . In: European Journal of Mineralogy . tape 25 , no. 1 , 2013, p. 113–115 , doi : 10.1127 / 0935-1221 / 2013 / 0025-22678 (English, pdfs.semanticscholar.org [accessed January 20, 2020]).
  3. ↑ 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 .
  4. ↑ Malcolm Back, William D. Birch, Michel Blondieau and others: The New IMA List of Minerals - A Work in Progress - Updated: January 2020. (PDF; 1762 kB) In: cnmnc.main.jp. IMA / CNMNC, Marco Pasero, January 2020, accessed January 20, 2020 .
  5. ^ 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.  659 (English).
  6. ^ Minerals with Cs-Ca-Si-O-H-F. In: mindat.org. Hudson Institute of Mineralogy, accessed January 20, 2020 .
  7. ↑ Localities for Fluorapophyllite- (Cs). In: mindat.org. Hudson Institute of Mineralogy, accessed January 17, 2020 .
  8. ↑ a b List of locations for fluorapophyllite (Cs) in the Mineralienatlas and Mindat (accessed on January 20, 2020)
  9. ↑ Fluorapophyllite- (Cs). In: mindat.org. Hudson Institute of Mineralogy, accessed January 20, 2020 .