Elpidite

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Elpidite
Elpidite-177602.jpg
Elpidite from the Poudrette Quarry , Montérégie , Québec , Canada
General and classification
chemical formula Na 2 Zr [Si 6 O 15 ] • 3H 2 O
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.DG.65 ( 8th edition : VIII / F.23)
72.05.04.02
Crystallographic Data
Crystal system Orthorhombic
Crystal class ; symbol orthorhombic-pyramidal; mm 2
Space group Pbcm (No. 57)Template: room group / 57
Lattice parameters a  = 7.1280 to 7.1312  Å ; b  = 14.644 to 14.6853 Å; c  = 14.6349 to 14.642 Å
Formula units Z  = 4
Twinning Observed
Physical Properties
Mohs hardness 5
Density (g / cm 3 ) measured: 2.52 to 2.62; calculated: 2.59
Cleavage completely after {110}
Break ; Tenacity splintery
colour colorless, white, yellowish, light to dark orange, brownish, beige, green
Line color White
transparency translucent to opaque
shine Silk gloss, pearlescent or wax gloss to matt
Crystal optics
Refractive indices n α  = 1.556 to 1.563
n β  = 1.565 to 1.569
n γ  = 1.574 to 1.577
Birefringence δ = 0.014
Optical character biaxial positive
Axis angle 2V = measured: 76 ° to 89 °
Other properties
Chemical behavior very soluble in hydrofluoric acid , somewhat soluble in sulfuric acid

Elpidite is a rather rare mineral belonging to the mineral class of silicates and germanates . It crystallizes in the orthorhombic crystal system with the chemical composition Na 2 Zr [Si 6 O 15 ] · 3H 2 O and is thus chemically a water-containing sodium - zirconium- silicate. Structurally , Elpidit belongs to the chain and band silicates .

Elpidit develops prismatic to columnar crystals that can reach a size of 30 cm. It can also appear fibrous or massive.

With a Mohs hardness of 5, elpidite is one of the medium-hard minerals.

Etymology and history

The mineral was discovered by Gustaf Lindström in Greenland in 1894 . He named it after the Greek word for hope (old Greek: ἐλπίς, -ίδος f , neugr .: ελπίδα). In 1964, Nina Nikolayevna Neronowa and Nikolai Wassiljewitsch Below examined the mineral for its crystal structure. They found an orthorhombic structure. They came to the lattice parameters a  = 7.4  Å , b  = 14.4 Å and c  = 7.05 as well as 2 formula units per unit cell . In 1973 these lattice parameters were corrected by the researchers E. Cannillo, G. Rossi and L. Ungaretti, to a  = 7.14 Å, b  = 14.68 Å and c  = 14.28 Å as well as 4 formula units per unit cell.

classification

Already in the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the elpidite belonged to the mineral class of "silicates and germanates" and there to the department of " chain silicates and band silicates (inosilicates)", where together with Terskit he formed the "Elpidite group" with the system no. VIII / F.23 .

The 9th edition of the mineral classification according to Strunz , which has been valid since 2001 and is used by the International Mineralogical Association (IMA), also classifies the Elpidit in the "chain and band silicates" department. This is, however, further subdivided according to the length and shape of the silicate chains, so that the mineral can be found according to its composition in the sub-section "Chain and band silicates with 3-periodic single and multiple chains", where it is the only member of the unnamed group 9 .DG.65 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the elpidite to the class of "silicates and Germanates" and there in the department of "layered silicates: two-dimensional unlimited layers with rings other than six-membered". Here it can be found together with Armstrongit in an unnamed group with the system number 72.05.04 within the sub-section “ Layered silicates: two-dimensional unlimited layers with rings other than six-membered: corroded and complex layers”.

Crystal structure

To the crystallographic analyzes by AA Grigor'eva, NV Zubkova, IV Pekov, Uwe Kolitsch, D. Yu. According to Pushcharovsky, MF Vigasina, G. Giester, T. Dordević, E. Tillmanns and NV Chukanov from 2011, elpidite crystallizes orthorhombically in the space group Pbcm (space group no.57 ) with the lattice parameters a  = 7.1280 to 7.1312  Å , b  = 14.644 to 14.6853 Å and c  = 14.6349 to 14.642 Å and 4 formula units per unit cell . Template: room group / 57

Another measurement also showed an orthorhombic symmetry, but with a different setup in the space group Cmce (space group no. 64) with the lattice parameters a  = 14.2999 Å, b  = 14.4408 Å and c  = 14.7690 Å. Template: room group / 64

properties

Elpidit is very soluble in hydrofluoric acid and somewhat soluble in sulfuric acid .

Education and Locations

About 40 sites of Elpidit are known.

The type locality , i.e. the place of the first description, is at Igaliku near Narsaq in Greenland .

The mineral was also found in the Canadian provinces of Ontario , Québec and Newfoundland and Labrador , in Kazakhstan , in Malawi near the city of Zomba, and in Morocco in Meknès-Tafilalet . The mineral was also found in Mongolia in the Gobi desert and in Chowd-Aimag , in Norway in Oppland and Vestfold , in Portugal on the autonomous archipelago of the Azores , in Russia in Siberia and northwestern Russia , in the United Kingdom in Scotland and in the US state of Arkansas , New Mexico , Utah, and Washington found.

See also

literature

  • G. Lindström: Elpidit, ett nytt mineral från Igaliko . In: Geologiska Föreningens i Stockholm Förhandlingar . tape 16 , no. 4 , 1894, pp. 330-335 ( PDF ).
  • Kenneth L. Currie, Eva Zaleski: The relative stability of elpidite and vlasovite: a PT indicator for peralkaline rocks . In: Canadian Mineralogist . tape 23 , 1985, pp. 577-582 ( PDF ).

Web links

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

Individual evidence

  1. ↑ a b Stefan Weiß: The large Lapis mineral directory. All minerals from A - Z and their properties . 6th completely revised and supplemented edition. Weise, Munich 2014, ISBN 978-3-921656-80-8 .
  2. ↑ a b IMA / CNMNC List of Minerals; May 2015 (PDF 1.6 MB; p. 52).
  3. ↑ a b c d e f g h i Elpidite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy . Mineralogical Society of America, 2001 ( PDF ).
  4. ↑ a b c AA Grigor'eva, NV Zubkova, IV Pekov, Uwe Kolitsch , D. Yu. Pushcharovsky, MF Vigasina, G. Giester, T. Dordević, E. Tillmanns, NV Chukanov: Crystal chemistry of elpidite from Kahn Bogdo (Mongolia) and its K- and Rb-exchanged forms. In: Crystallography Reports. Volume 56, 2011, pp. 832-841.
  5. ↑ a b c Mineralienatlas: Elpidit
  6. ↑ a b Mindat - Elpidite (English).
  7. ↑ NN Nero Nova NV Belov: Crystal Structure of elpidite, Na 2 Zr [Si 6 O 15 ] · 3H20 . In: Soviet Physics - Crystallography . tape 9 , 6 (May – June), 1965 ( PDF ).
  8. ↑ Elio Cannillo, Giuseppe Rossi, Luciano Ungaretti: The Crystal Structure of Elpidite . In: American Mineralogist . 58 (May – June), 1973, pp. 106-109 ( PDF ).
  9. ↑ The former name of this group of rooms was Ccma .
  10. ↑ Find location list for Elpidit in the Mineralienatlas and Mindat .