Friedrichbeckeit

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Friedrichbeckeit
General and classification
chemical formula KNa □ Mg 2 Be 3 Si 12 O 30
Mineral class
(and possibly department) 		Silicates and germanates - ring silicates
System no. to Strunz
and to Dana 		9.CM.05
63.02.01a.21
Crystallographic Data
Crystal system hexagonal
Crystal class ; symbol dihexagonal-dipyramidal; 6 / m  2 / m  2 / m
Space group P 6 / mcc (No. 192)Template: room group / 192
Lattice parameters a  = 9.970  Å ; c  = 14,130 Å
Formula units Z  = 2
Frequent crystal faces {0001}, subordinate to {10 1 0}, {11 2 0}
Physical Properties
Mohs hardness 6th
Density (g / cm 3 ) 2,686 (calculated)
Cleavage -
Break ; Tenacity irregular
colour colorless to pale yellow
Line color White
transparency transparent
shine Glass gloss
Crystal optics
Refractive indices n ω  = 1.552
n ε  = 1.561
Birefringence δ = 0.009
Optical character uniaxial positive, sometimes slightly biaxial
Pleochroism clear: ω = yellow; ε = light blue

The mineral Friedrichbeckeit is a very rare ring silicate from the milarite group and has the simplified chemical composition KNa □ Mg 2 Be 3 Si 12 O 30 . It crystallizes in the hexagonal crystal system and develops colorless, six-sided platy crystals less than a millimeter in size.

Friedrichbeckeit is formed during the contact metamorphosis of silica -rich foreign rock inclusions in alkali-rich tephritic magmas and has so far only been found at its type locality , the Bellerberg volcano in the Eifel .

Etymology and history

Was discovered in 2009 in a Friedrichbeckeit gneiss - Xenolith from Ettringer Bellerberg in the Eifel , Germany and was designed by CL Lengauer, N. Hrauda, U. Kolitsch, R. Krickl, and E. Tillmans after the Austrian mineralogist and petrographers Friedrich Johann Karl Becke ( 1855–1931). Becke was the head of the Mineralogical-Petrographic Institute of the University of Vienna and is known for the method he developed to estimate the refractive index of minerals under the microscope by observing the Becke line, which is also named after him .

Friedrichbeckeit is already the second attempt to honor Friedrich Becke by naming a mineral. Named as 1905 J. Morozewicz the calcium - lanthanum silicate Beckelith by Friedrich Becke. Beckelith was found to be identical to Britholite- (Ce) and was discredited as a mineral in 2006 by the CNMMC of the International Mineralogical Association (IMA).

classification

Since the Friedrichbeckeit was only discovered in 2009, it is not listed in the Strunz system of minerals (8th edition), which has been outdated since 2001 . Only in the “Lapis Mineralienverzeichnis” (6th edition) published in 2014, which, out of consideration for private collectors and institutional collections, is still based on the classic system of Karl Hugo Strunz , was the mineral given system no. VIII / E.22-20 and would thus become the “Milarit-Osumilith-Gruppe” with the system no. VIII / E.22 within the division of " ring silicates (cyclosilicates) ".

Friedrichbeckeit is not yet listed in the outdated, but partly still in use, 8th edition of the Strunz mineral classification. He would there with Almarudit , Armenit , Berezanskit , Brannockit , Chayesit , Darapiosit , Dusmatovit , Emeleusit , Faizievit , Merrihueit , Oftedalit , Osumilith , Osumilith- (Mg) , Poudretteit , Roedderit , Shibkovit , Sogdianit , Sugilith , Trattnerit and Yagiit the general ward the " ring silicates (cyclosilicates)" in the " Milarit-Osumilith group " with the system no. VIII / E.22 .

The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and is used by the International Mineralogical Association (IMA), also classifies the Friedrichbeckeit in the "ring silicates" section. This is, however, further subdivided according to the structure of the rings, so that the mineral can be found in the sub-section "[Si 6 O 18 ] 12− -six double rings" according to its structure . With Almarudit, Armenit, Berezanskit, Brannockit, Chayesit, Eifelit , Darapiosit, Dusmatovit, Klöchit , Merrihueit, Milarit, Oftedalit, Osumilith, Osumilith- (Mg), Poudretteit, Roedderite, Shibkovite, Sogdianite, Sugil " Milaritgruppe " with the system no. 9.CM.05 .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Friedrichbeckeit to the class of "silicates and Germanates", but there in the more finely subdivided division of "ring silicates: condensed rings". Here it is in the " Milarite Osumilith Group (Milarite Osumilith Subgroup) " with the system no. 63.02.01a can be found in the subsection “ Ring Silicates : Condensed, 6-membered Rings”.

Chemism

Friedrichbeckeit is the Mg analogue of Almarudit, Milarit and Oftedalit or the Be analogue of Merrihueit and Roedderite and the measured composition from the type locality is [12] (K 0.87 ) [9] (Na 0.86 □ 1, 16 ) [6] (Mg 1.57 Mn 0.28 Fe 0.24 ) [4] (Be 1.83 Mg 1.17 ) [4] Si 12.0 O 30 , with the coordination number of the in square brackets respective position in the crystal structure is indicated.

The ideal end link composition of Friedrichbeckeit does not contain any magnesium at the [4] T2 position. The composition measured from the type locality corresponds to a Friedrichbeckeit-Roedderite mixed crystal with ≈ 30% roedderite content.

Crystal structure

Friedrichbeckeit crystallizes in the hexagonal crystal system in the space group P 6 / mcc (space group no.192) with the lattice parameters a  = 9.970  Å and c  = 14.130 Å as well as two formula units per unit cell .  Template: room group / 192

Friedrichbeckeit is isotypic to milarite , ie it crystallizes with the same structure as milarite. The 12-fold coordinated C position is almost fully occupied with potassium (K + ). The 9-fold coordinated B position is half occupied by sodium (Na + ). Magnesium (Mg 2+ ), manganese (Mn 2+ ) and iron (Fe 2+ ) fill the 6-fold coordinated A position and the tetrahedrally coordinated T2 position contains beryllium (Be 2+ ) and magnesium (Mg 2+ ) . The T1 position, which builds up the 6 double rings, only contains silicon (Si 4+ ).

Education and Locations

Friedrichbeckeit forms contact metamorphic at high temperatures around 900 ° C and low pressure. It is assumed that, like Eifelit , it is deposited directly from an alkali-rich , silicon and magnesium-containing and aluminum-poor gas phase.

The only documented occurrence of Friedrichbeckeit so far is its type locality , the quarry of the A. Casper company on Ettringer Bellerberg , 2 km north of Mayen , in the Laacher See region of the Eifel , Rhineland-Palatinate , Germany . This very mineral-rich site is the type locality of 13 minerals (as of 2016), 4 of which are from the milarite group: Almarudite , Eifelite , Friedrichbeckeit and Osumilith- (Mg) . The milarite group minerals chayesite, merrihueit, roedderite and trattnerite were also detected here.

There the mineral was found in cavities of a silicate-rich rock inclusion ( xenolite ) in leucite - tephrite - lava . It occurs together with quartz , sanidine , tridymite , augite , magnesio hornblende , enstatite , almandine - spessartine -rich garnet , fluorapatite , biotite , braunite , hematite and roedderite . This occurrence corresponds to those of the other minerals from the milarite group that were previously found in the Vulkaneifel : Almarudite , Roedderite, Osumilith and Osumilith- (Mg) .

See also

literature

  • Paul Ramdohr , Hugo Strunz : Klockmann's textbook of mineralogy . 16th edition. Ferdinand Enke Verlag, 1978, ISBN 3-432-82986-8 , pp. 714 .
  • Friedrichbeckeite . In: John W. Anthony, Richard A. Bideaux, Kenneth W. Bladh, Monte C. Nichols (Eds.): Handbook of Mineralogy, Mineralogical Society of America . 2001 ( handbookofmineralogy.org [PDF; 91 kB ; accessed on April 17, 2017]).

Web links

Individual evidence

  1. ↑ a b c d e f g h i j k l m n o p q r s t u v CL Lengauer, N. Hrauda, ​​U. Kolitsch, R. Krickl, E. Tillmanns: Friedrichbeckeite, K ( □ 0.5 Na 0.5 ) 2 (Mg 0.8 Mn 0.1 Fe 0.1 ) 2 (Be 0.6 Mg 0.4 ) 3 [Si 12 O 30 ], a new milarite-type mineral from the Bellerberg volcano, Eifel area, Germany . In: Mineralogy and Petrology . tape 96 , 2009, p. 221-232 , doi : 10.1007 / s00710-009-0050-9 .
  2. ↑ a b c d e f g h i j k l m n o p q r s t u v PC Piilionen, G. Poirier, and KT Tait: New Mineral Names. Friedrichbeckeite . In: American Mineralogist . tape 94 , 2009, p. 1495–1501 ( minsocam.org [PDF; 637 kB ]).
  3. ↑ Webmineral - Friedrichbeckeit (English)
  4. ↑ J. Morozewecz: About Beckelith, a cerium-lanthano-didymo-silicate of calcium . In: Chemaks mineralogical and petrographic communications . tape 24 , 1905, pp. 120-134 ( archive.org [accessed April 17, 2017]).
  5. ↑ Ernst AJ Burke: A mass discreditation of GQN Minerals . In: The Canadian Mineralogist . tape 44 , 2006, pp. 1557–1560 , doi : 10.2113 / gscanmin . 44.6.1557 .
  6. ↑ 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 .
  7. ↑ Caspar quarry, Bellerberg volcano, Ettringen, Mayen, Eifel, Rhineland-Palatinate, Germany (English)