Dalyite

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Dalyite
Dalyite.jpg
Pale brown dalyite crystal aggregates from Gjerdingen ( Oppland , Norway)
General and classification
chemical formula K 2 Zr [Si 6 O 15 ]
Mineral class
(and possibly department) 		Silicates and Germanates ( sheet silicates )
System no. to Strunz
and to Dana 		9.EA.25 ( 8th edition : VIII / E.02)
72.02.01.01
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Space group P 1 (No. 2)Template: room group / 2
Lattice parameters a  = 7.37  Å ; b  = 7.73 Å; c  = 6.91 Å
α  = 106.2 °; β  = 111.4 °; γ  = 100.0 °
Formula units Z  = 1
Frequent crystal faces { 1 01}, pinacoids parallel [001]
Twinning Contact twins with {100} as an adhesion level
Physical Properties
Mohs hardness 7.5
Density (g / cm 3 ) 2.84 (measured); 2.81 (calculated)
Cleavage clear after { 1 01} and {010}
indistinct after {100}
Break ; Tenacity brittle
colour colorless, white, pink-brown, purple
Line color White
transparency transparent
shine Glass gloss
radioactivity hardly detectable
Crystal optics
Refractive indices n α  = 1.575
n β  = 1.590
n γ  = 1.601
Birefringence δ = 0.026
Optical character biaxial negative
Axis angle 2V = 72 ° (measured); 80 ° (calculated)
Other properties
Chemical behavior Insoluble in nitric acid, easily soluble in hot hydrofluoric acid
Special features strong cathodoluminescence (azure blue)

Dalyit is a seldom occurring mineral from the mineral class of " silicates and germanates " with the chemical composition K 2 Zr [Si 6 O 15 ] and thus, from a chemical point of view, a potassium - zirconium silicate. Structurally, Dalyit belongs to the layered silicates (phyllosilicates).

Dalyit crystallizes in the triclinic crystal system and develops short prismatic crystals from 0.1 to 0.5 mm in size with a glass-like sheen on the surfaces as well as occasionally contact twins with {100} as an intergrowth plane. In its pure form, dalyite is colorless and transparent. However, due to multiple light refraction due to lattice construction defects or polycrystalline training, it can also be translucent white and take on a pink-brown or purple color due to foreign admixtures.

Etymology and history

The mineral was discovered by Cecil Edgar Tilley while examining thin sections of rock samples collected from Green Mountain and Middleton Peak on the island of Ascension , which is part of the British overseas territory of St. Helena, Ascension and Tristan da Cunha . At his instigation, after preliminary investigations by Stuart O. Agrell, who also isolated the first crystal, René van Tassel and Max Hey first described the dalyite in 1952 . Van Tassel named the mineral after the Canadian geologist Reginald Aldworth Daly (1871-1957) as an appreciation for his services to the knowledge of the geology and petrology of the island of Ascension.

The type material of the mineral is stored in the Institut royal des Sciences naturelles de Belgique in Brussels , Belgium (catalog number C1430), in the Natural History Museum in London , United Kingdom (catalog number BM 64685) and in the National Museum of Natural History in Washington, DC , USA (Catalog No. 113106).

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , Dalyit belonged to the mineral class of "silicates and germanates" and there to the department of "phyllosilicates", where it was the sole representative of the unnamed group VIII / E. 02 made.

In the last revised and updated Lapis mineral directory by Stefan Weiß in 2018 , which, out of consideration for private collectors and institutional collections, is still based on this classic system of Karl Hugo Strunz , the mineral was given the system and mineral number. VIII / H.03-20 . In the “lapis system” this also corresponds to the “layered silicates” department, where dalyite and davanite form an independent but unnamed group.

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 classifies dalyite in the “layered silicates” department. This is, however, further subdivided according to the structure of the layers, so that the mineral, according to its structure, can be found in the sub-section "Simple tetrahedral networks with 4, 5, (6) and 8-membered rings", where it is named after the "Dalyit group" with the system no. 9.EA.25 and the other member forms davanite.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , also assigns Dalyit to the class of "silicates and Germanates" and there in the department of "layered silicate minerals". Here, too, he is the namesake of the "Dalyit Group" with the system no. 72.02.01 and the other members Davanit, Sazhinit- (Ce) and Sazhinit- (La) within the sub-section " Layered silicates: two-dimensional unlimited layers with rings other than six-membered: 4-, 6-, and 8-membered rings ".

Chemism

According to the idealized chemical formula K 2 Zr [Si 6 O 15 ], dalyite consists of 13.53% potassium (K), 15.78% zirconium (Zr), 29.16% silicon (Si) and 41.53% oxygen ( O).

In type material of the island Ascension however, 15% of potassium were approximately ions by sodium ions substituted , corresponding to a weight proportion of 1.75% Na 2 O . Further, the sample contained small amounts of Fe 2 O 3 and H 2 O . A sample from Dalsfjord in Norway only contained traces of sodium, but part of the zirconium was replaced by titanium in the form of 1.23% TiO 2 . The sample also contained small amounts of FeO and traces of Al 2 O 3 , CaO , MgO , MnO , BaO and P 2 O 5 . In general, the substitution of potassium by sodium in peralkaline granites and syenites is more pronounced than in alkaline rocks with a clear predominance of potassium ( highly potassic, K 2 O / Na 2 O> 2), while the substitution of zirconium by titanium and the storage of iron in alkaline rocks with a clear predominance of potassium is more significant than in peralkaline granites and syenites.

Crystal structure

Silicate tetrahedron layer of dalyite

Dalyit crystallizes triclinically in the space group P 1 (space group no. 2) with the lattice parameters a  = 7.37  Å ; b  = 7.73 Å; c  = 6.91 Å; α = 106.2 °; β = 111.4 ° and γ = 100.0 ° and one formula unit per unit cell . Template: room group / 2

Structurally Dalyit is a layer silicate whose SiO 4 - tetrahedra are arranged as three monolayers. The layers consist of chains of corner-linked SiO 4 tetrahedra, which are connected to form four-, six- and eight-membered rings. Within the chains, the orientation of the tetrahedra to each other is repeated, as with wollastonite, after every three links. The silicate layers are regular ZrO 6 - octahedron and irregular (K, Na) O 8 - polyhedron interconnected.

properties

With a Mohs hardness of 7.5, Dalyite is one of the hard minerals and is just able to scratch the reference mineral quartz (hardness 7). Its density is measured 2.84 g / cm 3 and calculated 2.81 g / cm 3 .

Dalyit is not attacked by warm concentrated nitric acid (HNO 3 ). It is slowly attacked by cold hydrofluoric acid (HF), but it is easily soluble in hot hydrofluoric acid.

Like all potassium minerals, Dalyit has a weak radioactivity that can be detected with sensitive instruments due to its natural 40 K content .

When bombarded with electrons , dalyite shows strong cathodoluminescence in a light azure blue .

Education and Locations

Crystal aggregates of dalyite (pale brown) with a little Janhaugite (orange brown) from Gjerdingen (Oppland, Norway)

Dalyite forms as a rare accessory component in various igneous rocks . It was first discovered in ejections made of alkali granite in trachytic and basaltic tuffs from Ascension . In the meantime it could be found in other places in syenites , pegmatites , charoitites , lamproites , lamprophyren , fenites and carbonatites .

As a rare mineral formation, dalyite could only be detected in a few places worldwide, with around a dozen sites being documented (as of 2018). At its type locality Green Mountain and other sites on the Atlantic island of Ascension, which belongs to the British overseas territory of St. Helena, Ascension and Tristan da Cunha , it appeared accompanied by aegirine , aenigmatite , arfvedsonite and quartz . Dalyite was also found on the Azores islands Terceira and São Miguel (volcano Água de Pau , here together with sanidine , arfvedsonite, quartz, aegirine, fayalite , astrophyllite and chevkinite (Ce) ), which belong to Portugal .

The only sites on the European mainland are the Cancarix volcano in the Spanish province of Albacete as well as the Dalsfjord in the province of Vestland in Norway and the lake Gjerdingen near Lunner in the province of Innlandet (here together with pyrophanite , elpidite , monazite , kupletskit and that of this Source of the first described Janhaugit ).

The Murun massif in the Aldan highlands in the Sakha Republic , which belongs to the Russian Federation , the Brandberg area in the Namibian region of Erongo , the Gordon Butte in the US state of Montana , the Strange Lake (Lac Brisson) on the border between the Canadian provinces of Québec and Newfoundland and Labrador as well as Straumsvola in Queen Maud country claimed by Norway in Antarctica.

use

Due to its rarity, dalyite is only of interest to the mineral collector and research.

See also

literature

Web links

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

Individual evidence

  1. ↑ a b c d e Hugo Strunz , Ernest H. Nickel : Strunz Mineralogical Tables. Chemical-structural Mineral Classification System . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p.  660 .
  2. ↑ a b c David Barthelmy: Dalyite Mineral Data. In: webmineral.com. Retrieved August 18, 2019 .
  3. ↑ a b c d e f g h i j k l m Dalyite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 (English, handbookofmineralogy.org [PDF; 77  kB ; accessed on August 18, 2019]).
  4. ↑ a b 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 .
  5. ↑ a b c d e Dalyite. In: mindat.org. Hudson Institute of Mineralogy, accessed August 18, 2019 .
  6. ↑ a b c d René van Tassel, Max H. Hey : Dalyite, a new potassium zirconium silicate, from Ascension Island, Atlantic . In: Mineralogical Magazine and Journal of the Mineralogical Society . tape 29 , no. 217 , June 1952, ISSN  0369-0148 , p. 850–857 , doi : 10.1180 / minmag.1952.029.217.02 (English, rruff.info [PDF; 350 kB ]).
  7. ↑ Michael Fleischer : New Mineral Names: Dalyite . In: American Mineralogist . tape  37 , no. 11-12 , 1952, ISSN  0003-004X , pp. 1071 (English, minsocam.org [PDF; 247 kB ; accessed on August 18, 2019]).
  8. ↑ Catalog of Type Mineral Specimens - D. (PDF; 50 kB) In: Catalog of Type Mineral Specimens (CTMS). International Mineralogical Association - Commission on Museums, accessed August 18, 2019 .
  9. ↑ Ernest H. Nickel, Monte C. Nichols: IMA / CNMNC List of Minerals 2009. (PDF; 1.88 MB) In: cnmnc.main.jp. IMA / CNMNC, January 2009, accessed August 18, 2019 .
  10. ↑ Dalyit. In: Mineralienatlas Lexikon. Stefan Schorn u. a., accessed on August 18, 2019 .
  11. ^ Brian Robins, Harald Furnes, Paul Ryan: A new occurrence of dalyite . In: Mineralogical Magazine . tape 47 , no. 342 , March 1983, ISSN  0026-461X , p. 93–94 , doi : 10.1180 / minmag.1983.047.342.21 (English, rruff.info [PDF; 145 kB ; accessed on August 18, 2019]).
  12. ↑ Piero Comin-Chiaramonti, Celso Barros Gomes (ed.): Alkaline magmatism in central-eastern Paraguay: relationships with coeval magmatism in Brazil . Editora da Universidade de São Paulo, São Paulo 1995, ISBN 85-314-0362-6 , Magmatism in eastern Paraguay: occurrence and petrography - Classification and nomenclature, p. 105 (English, limited preview in Google Book Search).
  13. ^ A b Adam J. Jeffery et al .: On the compositional variability of dalyite, K 2 ZrSi 6 O 15 : a new occurrence from Terceira, Azores . In: Mineralogical Magazine . tape 80 , no. 4 , June 1, 2016, ISSN  0026-461X , p. 547–565 , doi : 10.1180 / minmag.2016.080.018 (English, Accepted Manuscript available as eprint from Keele University [PDF; 1.1 MB ; accessed on August 18, 2019]).
  14. ↑ Stephen G. Fleet: The crystal structure of dalyite . In: Journal of Crystallography - Crystalline Materials . tape 121 , no. 1-6 , November 1, 1965, pp. 349–368 , doi : 10.1524 / zkri.1965.121.16.349 (English, rruff.info [PDF; 780 kB ; accessed on August 18, 2019]).
  15. ↑ a b List of locations for dalyite in the Mineralienatlas and Mindat
  16. ↑ Photo Search: Dalyite with Chevkinite- (Ce). In: mindat.org. Hudson Institute of Mineralogy, accessed February 5, 2019 .