Eudidymite
| Eudidymite | |
|---|---|
 |
|
| General and classification | |
| chemical formula | Na 2 Be 2 [4] [Si 6 O 15 ] • H 2 O |
|
Mineral class (and possibly department) |
Silicates and Germanates |
|
System no. to Strunz and to Dana |
9.DG.60 ( 8th edition : VIII / G.04) 66.03.01.03 |
| Crystallographic Data | |
| Crystal system | monoclinic |
| Crystal class ; symbol | monoclinic prismatic; 2 / m |
| Space group | C 2 / c (No. 15) |
| Lattice parameters |
a = 12.63 Å ; b = 7.38 Å; c = 14.02 Å β = 103.7 ° |
| Formula units | Z = 4 |
| Twinning | after {001} lamellar (polysynthetic) twins |
| Physical Properties | |
| Mohs hardness | 6th |
| Density (g / cm 3 ) | measured: 2.55; calculated: 2.57 |
| Cleavage | perfect after {001} imperfect after { 5 51} |
| Break ; Tenacity | shell-like to uneven |
| colour | colorless to white; rarely also gray-blue, blue, violet or yellow |
| Line color | White |
| transparency | transparent to translucent |
| shine | Glass luster, pearlescent luster on the gap surfaces |
| Crystal optics | |
| Refractive indices |
n α = 1.545 n β = 1.546 n γ = 1.551 |
| Birefringence | δ = 0.006 |
| Axis angle | 2V = measured: 30 °; calculated: 50 ° |
The mineral eudidymite is a rarely occurring chain silicate from the mineral class of " silicates and germanates ". It crystallizes in the monoclinic crystal system with the chemical composition Na 2 Be 2 [4] [Si 6 O 15 ] · H 2 O and often develops tabular and twisted crystals of up to a few centimeters in size that are either colorless or white in color. Gray-blue, blue, purple or yellow eudidymites are also rarely found.
Etymology and history
Eudidymite was first found in 1887 on the island of Lille Arøya in the Langesundsfjord in the Norwegian province of Vestfold and described by Waldemar Christofer Brøgger , who used the Greek words εὖ eu- for “good” and δίδυμος didymos for “twin” because of its frequent twinning. named.
classification
In the outdated, but partly still in use 8th edition of the mineral classification according to Strunz , the eudidymite belonged to the department of "Silicates and Germanates with transition structures between chain and layered silicates", where with epididymite it belongs to the group of the same name with the system no. VIII / G.04 .
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 eudidymite in the category of "chain and band silicates (inosilicates)". This is further subdivided according to the crystal structure, so that the mineral can be found according to its structure in the sub-section "Chain and band silicates (inosilicates) with 3-periodic single and multiple chains", where it is the only member of the unnamed group 9.DG .60 forms.
The systematics of minerals according to Dana , which is common in the English-speaking world , also sorts the eudidymite into the section of chain silicates, but there in the sub-section of " chain silicates with double, unbranched chains, W = 2 with chains P> 2 ", where it, together with xonotlite , Zorite , Epididymit, Yuksporit , Haineaultit and Chivruaiit form the group 66.03.01 with P = 3 .
Crystal structure
Eudidymite crystallizes monoclinically in the space group C 2 / c (space group no. 15) with the lattice parameters a = 12.63 Å ; b = 7.38 Å; c = 14.02 Å and β = 103.7 ° as well as four formula units per unit cell .
Modifications and varieties
The compound Na 2 Be 2 [4] [Si 6 O 15 ] • H 2 O is dimorphic and crystallizes as an orthorhombic epididymite in addition to the monoclinic eudidymite .
Education and Locations
Eudidymit formed as a late phase in alkaline nepheline - syenite or - pegmatite . Accompanying minerals include aegirine , albite , analcime , elpidite , fuorite , natrolite , neptunite and quartz .
Worldwide, Eudidymite has so far (as of 2010) been found at around 30 sites, for example at Arenópolis in the Brazilian state of Goiás ; at Mont Saint-Hilaire ( Québec ) and at Letitia Lake in Labrador , Canada ; near Věžná in the Czech Republic; in the Kitaa region of Greenland; at Mount Malosa in Malawi ; in several regions of Vestfold and Telemark in Norway; on Zagi Mountain near Mulla Ghori (Khyber Agency) in the federally administered tribal areas in Pakistan; on Kola and in Eastern Siberia in Russia and at Okehampton in England.
See also
literature
- Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 , pp. 737 .
Web links
Mineral Atlas: Eudidymite (Wiki)
Individual evidence
- ↑ Webmineral - Eudidymite (English)
- ↑ a b c d 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. 639 .
- ↑ a b Eudidymite , In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America , 2001 ( PDF 68.6 kB )
- ↑ a b c d Mindat - Eudidymite
- ↑ Find location list for eudidymite in the Mineralienatlas and in Mindat