Euclas

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Euclas
Euclase-274943.jpg
Euclas crystal (size: 4.0 cm × 3.3 cm × 1.5 cm) from Espírito Santo, Brazil
General and classification
chemical formula BeAl [OH | SiO 4 ]
Mineral class
(and possibly department) 		Silicates (and germanates) - island silicates (nesosilicates)
System no. to Strunz
and to Dana 		9.AE.10 ( 8th edition : VIII / B.01)
02.02.01.01
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic; 2 / m
Space group P 2 1 / a (No. 14, position 3)Template: room group / 14.3
Lattice parameters a  = 4.780  Å ; b  = 14.322 Å; c  = 4.6335 Å
β  = 100.31 °
Formula units Z  = 4
Physical Properties
Mohs hardness 7.5
Density (g / cm 3 ) 2.99 to 3.1
Cleavage completely after {010}
Break ; Tenacity shell-like to uneven
colour colorless, blue, greenish, yellowish
Line color White
transparency transparent to translucent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.652
n β  = 1.655
n γ  = 1.671
Birefringence δ = 0.019
Optical character biaxial positive
Axis angle 2V = 50 °
Pleochroism not available or colorless

Euclas is a rarely occurring mineral from the mineral class of island silicates (nesosilicates). It crystallizes in the monoclinic crystal system with the chemical composition BeAl [OH | SiO 4 ] and develops mostly short to long, prismatic crystals , but also radial or granular aggregates which can be either colorless or blue, greenish or yellowish in color due to foreign admixtures.

Etymology and history

First found and described the Euclase 1792 was Haüy who it because of its perfect cleavage along the Greek words εὐ- eu "good" and κλάσις Klasis named "Breaking, breaking".

classification

In the old systematics of minerals (8th edition) according to Strunz , the Euclas is sorted into the division of island silicates with non-tetrahedral anions (Neso-subsilicates). Since the 9th edition of this systematics , however, due to the finer subdivision, the mineral has been in the division of "Island silicates with additional (O, OH, F, H 2 O) and cations in tetrahedral [4] and mostly greater coordination".

The systematics of the minerals according to Dana assigns the Euclas to the department "Nesosilicates Nesosilicate Insular SiO 4 Groups and O, OH, F, and H2O with cations in [4] and> [4] coordination", where he together with Klinoedrite , Hodgkinsonit and Gerstmannite forms the Euklas group .

Crystal structure

Euklas crystallizes monoclinically in the space group P 2 1 / a (space group no. 14, position 3) with the lattice parameters a  = 4.780  Å ; b  = 14.322 Å, c  = 4.6335 Å and β = 100.31 ° as well as four formula units per unit cell . Template: room group / 14.3

Education and Locations

Euclas is mainly formed by hydrothermal processes in pegmatites , greisen and quartz, among others .

So far the mineral has been found in the following regions (as of 2009): Province of Luxembourg in Belgium; Minas Gerais and Rio Grande do Norte in Brazil; Hunan and Jiangxi in the People's Republic of China; Bavaria (Fichtelgebirge) and Saxony (Vogtland) in Germany; in western Finland ; England in Great Britain; Trentino-South Tyrol in Italy; Boyacá in Colombia; Zambezia in Mozambique; Erongo in Namibia; Aust-Agder in Norway; Carinthia , Salzburg and Tyrol in Austria; Ancash in Peru; Eastern Siberia in Russia; Ångermanland , Södermanland and Västmanland in Sweden; Ticino in Switzerland; Sabaragamuwa in Sri-Lanka; Bohemia and Moravia in the Czech Republic; Zhytomyr Oblast in Ukraine; as well as Alaska , Colorado , Connecticut , Maine , Michigan , New Hampshire , New Mexico , North Carolina , Texas , Virginia and Wisconsin in the United States.

Use as a gem stone

Blue Euclas in gem quality

Euclas is a coveted gemstone with good quality ; especially its blue varieties, which are comparable to aquamarine and sapphire . Due to its perfect cleavability, however, it reacts very sensitively to pressure and too rapid temperature changes, such as those that occur during soldering and setting and can cause the stone to burst.

See also

literature

Web links

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

Individual evidence

  1. ↑ Webmineral - Euclase (English)
  2. ↑ a b c American Mineralogist Crystal Structure Database (engl., 1986)
  3. ↑ a b c Mindat - Euclase (English)
  4. ↑ Stefan Weiß: The large Lapis mineral directory . 5th edition. Christian Weise Verlag, Munich 2008, ISBN 3-921656-17-6 .
  5. ↑ Find location list for Euclas in the Mineralienatlas and in Mindat
  6. ↑ Gem etiquette from Prof. Leopold Rössler - Euklas