Ilvait

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Ilvait
Ilvaite-Quartz-233498.jpg
Ilvaite and quartz from Serifos , Greece (size: 3.9 × 2.1 × 1.8 cm)
General and classification
chemical formula Ca (Fe 2+ ) 2 Fe 3+ [O | OH | Si 2 O 7 ]
Mineral class
(and possibly department) 		Silicates and Germanates
System no. to Strunz
and to Dana 		9.BE.07 ( 8th edition : VIII / C.10)
02.56.03.03
Crystallographic Data
Crystal system monoclinic
Crystal class ; symbol monoclinic prismatic 2 / m
Room group (no.) P 2 1 / a (No. 14)
Lattice parameters a  = 13.01  Å ; b  = 8.80 Å; c  = 5.85 Å
β  = 90.2 °
Formula units Z  = 4
Physical Properties
Mohs hardness 5.5 to 6
Density (g / cm 3 ) measured: 3.99 to 4.05; calculated: 4.064
Cleavage Please complete!
Break ; Tenacity uneven, brittle
colour black to black-gray
Line color black
transparency opaque; translucent in thin layers
shine weak metallic luster, matt
Crystal optics
Refractive indices n α  = 1.727
n β  = 1.870
n γ  = 1.883
Birefringence δ = 0.156
Optical character biaxial positive
Axis angle 2V = measured: 20 to 30 °; calculated: 30 °
Pleochroism strong in thin layers:
X = dark green
Y = yellow-brown to dark brown
Z = dark brown

Ilvait (also Lelievre , Lievrit , Jenit or Yenit ) is a mineral from the mineral class of " silicates and germanates ", which can sometimes be abundant in various locations, but is generally not very common. It crystallizes in the monoclinic crystal system with the chemical composition Ca (Fe 2+ ) 2 Fe 3+ [O | OH | Si 2 O 7 ] and develops mostly prismatic crystals , but also radial and grainy to massive mineral aggregates of black to grayish black in color with black line color .

With a Mohs hardness of 5.5 to 6, ilvaite is one of the medium-hard minerals that can be scratched with a steel file. The surfaces of the usually opaque crystals have a weak metallic sheen . Fractured surfaces or aggregate forms , on the other hand, are matt. Ilvaite is translucent in thin layers and shows strong pleochroism , i.e. depending on the direction from which the light beam falls through the crystal, the mineral changes its color from dark green to yellow-brown to dark brown.

Special properties

In front of the soldering tube , Ilvait easily melts into a black, glass-like and magnetic ball.

Etymology and history

Ilvait was first discovered at the Torre di Rio , a cliff south of the port of Rio Marina on the Italian island of Elba , and described in 1811 by Henrich Steffens , who named the mineral after the old name Elbas ( Ilva , after the Ilvates who used to live there ). after he discarded the name Jenit or Yenit chosen by the French .

classification

In the now outdated, but still in use 8th edition of the mineral systematics according to Strunz , the Ilvait belonged to the mineral class of "silicates and germanates" and there to the department of " group silicates (sorosilicates)", where together with hennomartinite , itoigawaite , lawsonite , noelbensonite and Wöhlerit formed an independent 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 the Ilvait to the class of “silicates and germanates” and there in the department of “group silicates (sorosilicates)”. However, this section is further subdivided according to the type of group formation, the possible presence of further anions and the coordination of the cations , so that the mineral according to its composition and structure in the sub-section “Si 2 O 7 groups with additional anions; Cations in octahedral [6] and greater coordination ”can be found, where it only forms the unnamed group 9.BE.07 together with Manganilvaite .

The systematics of minerals according to Dana , which is mainly used in the English-speaking world , assigns the Ilvait to the class of “silicates and Germanates”, but there in the more finely subdivided division of “group silicates: Si 2 O 7 groups and O, OH, F and H 2 O “a. Here he is the namesake together with Lawsonit in the "Lawsonit-Ilvait-Gruppe" with the system no. 56.02.03 and the other members hennomartinite, noelbensonite, itoigawaite and manganilvaite within the sub-section " Group silicates: Si 2 O 7 groups and O, OH, F and H 2 O with cations in [4] and / or> [4] - Coordination ”.

Education and Locations

Ilvaite and quartz from South Mountain , Owyhee County , Idaho, USA (size: 22 × 14 × 14 mm)

Ilvaite forms in contact with metasomatic rocks and iron deposits, in metamorphic limonites and dolomite . Accompanying minerals include quartz , magnetite , hedenbergite , sphalerite and fluorite .

Altogether, Ilvait has so far (as of 2011) been found at around 170 sites. In addition to its type locality near Rio Marina, the mineral occurred in Italy in several places in the provinces of Livorno and Grosseto in Tuscany, on Sardinia and Monzoni in Trentino and in the provinces of Salerno (Campania), Genoa (Liguria), Sondrio and Varese (Lombardy ), Turin and Verbano-Cusio-Ossola (Piedmont).

The island of Serifos in Greece, where up to 30 cm long crystals were found, is worth mentioning due to the extraordinary Ilvait finds . At its type locality Rio Marina, crystals up to 10 cm long still appeared.

In Germany, Ilvait was found near Seelbach (Herborn) in Hesse, near Bad Harzburg and Clausthal-Zellerfeld in Lower Saxony, near Ahrbrück in Rhineland-Palatinate and in several places in the Saxon Ore Mountains .

In Austria, the mineral has so far only been found near Freienberg in Styria and at the Islitz Alp in the Umbaltal in Tyrol and in Switzerland so far only near Marmorera (Graubünden) and in the Binn valley (Valais).

Other locations are Argentina , Australia , Bolivia , Bulgaria , Chile , China , Canada , France , Greenland , Iceland , India , Japan , Kosovo , Mexico , Mongolia , New Zealand , Norway , Romania , Russia , Slovakia , South Africa , Sweden , Ukraine , England in the United Kingdom (Great Britain) and the United States of America (USA).

Crystal structure

Ilvait crystallizes monoclinically in the space group (space group no. 14) with the lattice parameters a  = 13.01  Å ; b  = 8.80 Å; c  = 5.85 Å and β = 90.2 ° and 4 formula units per unit cell .

See also

Individual evidence

  1. ↑ a b Stefan Weiß: The large Lapis mineral directory . 5th edition. Christian Weise Verlag, Munich 2008, ISBN 3-921656-17-6 .
  2. ^ A b c Hugo Strunz , Ernest H. Nickel: Strunz Mineralogical Tables . 9th edition. E. Schweizerbart'sche Verlagbuchhandlung (Nägele and Obermiller), Stuttgart 2001, ISBN 3-510-65188-X .
  3. ↑ Handbook of Mineralogy - Ilvaite (English, PDF 72.2 kB)
  4. ↑ a b c d e Ilvaite at mindat.org (English)
  5. ↑ Steffen Heinrichs: Complete Handbook of Oryktognosie , Hall 1811 (PDF 212.9 kB)

literature

Web links

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