Eudialyte

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Eudialyte
Eudialyte in Syenite.jpg
Eudialyte in Syenite from Brazil
General and classification
chemical formula Na 15 Ca 6 Fe 3 Zr 3 Si (Si 25 O 73 ) (O, OH, H 2 O) 3 (Cl, OH) 2
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.CO.10 ( 8th edition : VIII / E.25)
64.01.01.01
Crystallographic Data
Crystal system trigonal
Crystal class ; symbol ditrigonal-scalenohedral 3 2 / m
Space group R 3 m (No. 166)Template: room group / 166
Lattice parameters a  = 14.2646  Å ; c  = 30.186 Å
Formula units Z  = 12
Physical Properties
Mohs hardness 5.0 to 5.5
Density (g / cm 3 ) 2.74 to 3.1
Cleavage clearly after the base c {0001}, indistinctly after a
Break ; Tenacity uneven
colour pink to red, yellow-brown to red-brown
Line color White
transparency transparent to translucent
shine Glass gloss, matt
radioactivity weakly radioactive
Crystal optics
Refractive indices n ω  = 1.606 to 1.610
n ε  = 1.610 to 1.613
Birefringence δ = 0.004
Optical character uniaxial alternating

The mineral Eudialyt is a rarely occurring cyclosilicate from the mineral class of the silicates and Germanates . It crystallizes in the triclinic crystal system with the chemical composition Na 15 Ca 6 Fe 3 Zr 3 Si (Si 25 O 73 ) (O, OH, H 2 O) 3 (Cl, OH) 2 . It crystallizes in the trigonal crystal system and develops prismatic to tabular crystals , but also granular mineral aggregates in pink and red to brown in color.

Etymology and history

The name Eudialyt is made up of the Greek words εὖ [eû] "good, efficient" or as a prefix εὐ- [eu-] " good- " (related to the Mycenaean prefix e-u- / eu̯- /, the ancient Indian prefix su - [or vásu "good"] and the Hittite adjective assu for "good-"; originally from * ἐσύ- [esú] or * h 1 sú- ) as well as διάλυτος , which in turn is composed of διά "through, because of, apart ”(possibly related to [δίς]“ twice ”or δύω [dúɔː]“ two ”) and λύω [lúɔː]“ solve ”(etymology unclear).

Eudialyte was first described in 1819 by Friedrich Stromeyer , who named the mineral after its special property of being easily meltable and acid-soluble. The type locality is the Illimaussaq complex in Kitaa (Greenland).

classification

In the old (8th edition) and new systematics of minerals according to Strunz (9th edition) the eudialyte belongs to the division of ring silicates (cyclosilicates). However, the new Strunz'sche mineral classification now subdivides it more precisely according to the type and size of the SiO 4 tetrahedra joined together to form rings . According to its formula, eudialyte belongs to the subdivision of ring silicates with "[Si 9 O 27 ] 18− - Neuner rings".

The systematics of minerals according to Dana also assigns the eudialyte to the ring silicates, but here in the sub-section "Rings with other anions and insular silicate groups with mixed ring types". There it forms the eudialyte group named after it together with 18 other minerals .

Crystal structure

Eudialyte crystallizes in the trigonal crystal system in the space group R 3 m (space group no. 166) with the lattice parameters a  = 14.2646  Å and c  = 30.186 Å and 12 formula units per unit cell . Template: room group / 166

properties

Eudialyt is characterized by the fact that it is extremely easy to liquefy. In front of the soldering tube , it melts very quickly into a pale green colored glass bead without coloring the flame. The mineral is also very sensitive to acids . Even when cold acids are poured over it, eudialyte discolours very quickly and gelatinizes easily and completely. This property is not lost even after glowing, but for complete gelatinization it requires the participation of a weak digestion heat (about body temperature between 28 and 30 ° C or max. 40 ° C).

Eudialyte is weakly radioactive with a specific activity of around 158.2  Bq / g (for comparison: natural potassium 31.2 Bq / g).

Modifications and varieties

  • Eucolite , eucolite or barsanovite also contain cerium and lanthanum and is a softer variety of eudialyte with a different appearance.

Education and Locations

Eudialyte forms in igneous rocks such as nepheline - syenite or - pegmatite . There it occurs in paragenesis with aegirine , nepheline and / or microcline .

So far the mineral has been exposed at 139 sites (as of 2009), including in New South Wales , Queensland and Tasmania (Australia); the northern and southern to southeastern regions of Brazil ; Liaoning (China); except in its type locality Kitaa also in Tunu on Greenland; Los Island in Guinea (Africa); British Columbia , Québec (Mont St. Hilaire), Newfoundland and Labrador (Canada); Antsiranana in Madagascar; Langesundsfjord in Norway ; several regions in Russia (Kukisvumchorr, Khibinymassiv, Kola); Bohemia in the Czech Republic; as well as some regions of the USA .

Use as a gem stone

Eudialyte is occasionally used as a gemstone due to its lively color in connection with other minerals, for example in the rock syenite . It is usually offered in the form of tumbled stones or cabochons , but facet cuts have also been used.

See also

literature

  • Petr Korbel, Milan Novák: Encyclopedia of Minerals . Nebel Verlag, Eggolsheim 2002, ISBN 3-89555-076-0 , p. 218 .

Web links

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

Individual evidence

  1. ↑ a b c d Webmineral - Eudialyte (English)
  2. ↑ a b American Mineralogist Crystal Structure Database - Eudialyte (English, 1999)
  3. ↑ a b c Eudialyte at mindat.org (engl.)
  4. ↑ IMA / CNMNC - List of Mineral names, Eudyalite (English, PDF 1.8 MB, p. 83)
  5. ↑ American Mineralogist Crystal Structure Database - Eudialyte (English, 1999)
  6. ↑ MinDat - Localities for Eudialyte (English)
  7. ^ Walter Schumann: Precious stones and gemstones . 13th edition. BLV Verlag, 2002, ISBN 3-405-16332-3 , p. 228, 229 .
  8. ↑ Realgems - Eudialyt (with picture examples of cut stones)