Jennit

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Jennit
Jennite.jpg
White, needle-like Jennit crystals from Ettringer Bellerberg , Eifel, Rhineland-Palatinate, Germany
General and classification
other names

IMA 1965-021

chemical formula Ca 9 [(OH) 4 | Si 3 O 8 OH] 2  • 6H 2 O
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.DG.20 ( 8th edition : VIII / F.18)
02.56.04.11
Crystallographic Data
Crystal system triclinic
Crystal class ; symbol triclinic pinacoidal; 1
Room group (no.) P 1 (No. 2)
Lattice parameters a  = 10.58  Å ; b  = 7.27 Å; c  = 10.83 Å,
α  = 99.6 °; β  = 97.6 °; γ  = 110.2 °
Formula units Z  = 1
Physical Properties
Mohs hardness 3.5
Density (g / cm 3 ) measured: 2.32 to 2.33; calculated: [2.34]
Cleavage clearly after {001}
colour colorless, white
Line color White
transparency transparent to translucent
shine Glass gloss
Crystal optics
Refractive indices n α  = 1.548 to 1.552
n β  = 1.562 to 1.564
n γ  = 1.570 to 1.571
Birefringence δ = 0.022
Optical character biaxial negative
Axis angle 2V = measured: 74 °; calculated: 72 to 74 °
Other properties
Special features white fluorescence

The mineral jennite is a seldom occurring chain silicate from the mineral class of " silicates and germanates ". It crystallizes in the triclinic crystal system with the chemical composition Ca 9 [(OH) 4 | Si 3 O 8 OH] 2  • 6H 2 O and develops leafy crystals of white and line color stretched along the b-axis .

Etymology and history

Jennit was first discovered by Colonel Clarence Marvin Jenni (1896-1973) in the Crestmore Quarry in Riverside County in the US state of California and described in 1966 by AB Carpenter, RA Calmers, JA Gard, K. Speakman, HFW Taylor, who named the mineral after his First discoverers named.

In contrast to the first chemical analysis by Carpenter, Jennit does not contain any significant amounts of sodium , as some samples examined later showed.

classification

In the meanwhile outdated, but still in use 8th edition of the mineral systematics according to Strunz , the Jennit belonged to the mineral class of "silicates and germanates" and there to the department of " chain silicates and band silicates (inosilicates)", where together with Bustamit , Cascandit , Denisovit , Ferrobustamite , foshagite , pectolite , sérandite , vistepit , wollastonite-1A and wollastonite-2M formed a separate group.

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 assigns Jennit to the class of "silicates and germanates" and there in the department of "chain and band silicates (inosilicates)" a. This department is, however, further subdivided according to the type of chain formation, so that the mineral can be found according to its structure in the subdivision "Chain and band silicates with 3-periodic single and multiple chains", where it is the only member of the unnamed group 9. DG.20 forms.

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns Jennit to the class of "silicates and germanates" and there in the department of " group silicates : Si 2 O 7 groups and O, OH, F and H2O". Here he is with Baghdadit , Burpalit , Cuspidin , Låvenit , Wöhlerit , Niocalit , Hiortdahlit , Rosenbuschite , Hainit , Janhaugit , Komarovit , Natrokomarovit , Suolunit , Mongolit , Kristiansenit , Kochit and Marianoit in the "Cuspidin-Wohlerit group" with the system -No. 56.02.04 within the subsection " Group silicates: Si2O7 groups and O, OH, F and H 2 O with cations in [4] and / or> [4] coordination ".

Crystal structure

Unit cell by Jennit represented by a “molecular modeling” program .

Jennit crystallizes triclinically in the space group P 1 (space group no. 2) with the lattice parameters a  = 10.58  Å ; b  = 7.27 Å; c  = 10.83 Å; α = 99.6 °; β = 97.6 ° and γ = 110.2 ° and one formula unit per unit cell .

properties

At a temperature of around 90 ° C, Jennite changes into meta-Jennite with a monoclinic structure due to the release of crystal water .

Education and Locations

Jennite forms in a late phase of crystallization as a partial filling of cavities and veins in contact metamorphic rocks such as B. Skarn . Accompanying minerals include afwillite , calcite , oyelite , scawtite , spurrite and tobermorite .

As a rare mineral, Jennite has only been found at a few sites, so far (as of 2011) around 15 sites are known. In addition to its type locality Crestmore in California in the USA, the mineral was also found at Boisséjour in the French region of Auvergne , on the Zeilberg in Bavaria and on the Ettringer Bellerberg near Ettringen in North Rhine-Westphalia in Germany, in the Hatrurim basin of the Israeli Negev desert , in the Italian municipalities Montalto di Castro and Spoleto , on the Japanese island of Honshu , in the town of Zitacuaro in the Mexican state of Michoacan , on Lakargi in the Russian republic of Kabardino-Balkaria , in the Slovak community Vechec when, in Hotazel in the South African Kalahari located Wessels Mine and Fort Portal in Uganda.

Individual evidence

  1. ↑ a b c d e Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X , p. 638 .
  2. ↑ Webmineral - Jennite (English)
  3. ↑ a b Handbook of Mineralogy - Jennite (English, PDF 77.6 kB)
  4. ↑ a b c Jennite at mindat.org (engl.)
  5. ^ AB Carpenter, R. A. Calmers, JA Gard, K. Speakman, HFW Taylor: Jennite, A New Mineral
  6. ↑ Mindat - Number of locations for Jennit

literature

  • AB Carpenter, RA Calmers, JA Gard, K. Speakman, HFW Taylor: Jennite, A New Mineral , in: The American Mineralogist , Vol. 51, January-February 1966 ( PDF 1.02 MB )

Web links

Commons : Jennite  - collection of pictures, videos and audio files